c
I.lIIIEUTAliCE ABD AGRONOmC SIGRI.FlCABCB
OF ADVElrrITIOUS aOOT DBVBLOPMBNT DI
UD CWVEI (Trlfol1ua prateoae L.).
by
JeaD-llarc Moutpetlt
Depart_ut of Plant Science
Macdonald Caapu8 of HcCl11 Unlversity
Saf.nte-Amae de Bellevue. Quebec. Canada
July, 1991
A TBlSIS SUIIII'l"I'BD TG TBB r!CULT! or CJW)UA!'B STUDms
AIIID USBAICB DI PARTIAL FULfU·J.JIQT OP
TBI DQU1D1Œ1r1'S FOI. 'lBI DBClIBI 01'
MASTBI. or SCIBBCB
@)Jean-Karc: Hontpetit, 1991.
(
(
Suggested short title:
SECONDAIlY ROOT GROVl8 IN
RED CLOVER (Trifolf.UII pratenae L.).
Jean-Marc Montpetit
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POREWORD
This thesis is submitted in the form of original papers suitable
for journal publications.
The first section ls a literature review
presenting the theory and previous knowledge on this toplc.
ïhe next
three sections represent the body of the thesis (each Is a complete
manuscript).
The Iast section ls a general discussion and a synthesis
of the major conclusions.
This thesis format has been approved by the
Faculty of graduate Studies and Research, McGill University, and
follows the cooditi'ns outlined in the Guidelines Concerning Theaia
Preparation, section B.2 "Manuscripts and Authorship" whlch are as
follows:
"The candidate has the option, subject to the approval of the
Depart.ent, of including as part of the thesis the text, or duplicated
published text of an original paper, or papers.
- Manuscript-style theses must still conform to aIl other requirements
explained in the Guidelines Concerning Thesis Preparation.
- Additionai materlai (procedurai and design data as weIl as
descriptions of equipment) must be provided in sufficient detail (e.g.
in appendices) to allow clear and precise judgment to be made of the
importance and originality of the research reported.
- The thesis should be more than a mere collection of manuscripts
published or to be published. lt must include a general abstract, a
full introduction and literature review and a final overaii
conclusIon. Connectlng texts which provide !ogica! brIdges between
the different manuscripts are usually desirable in the Interest of
cohesion.
lt ls acceptable for theses to include, as chapters, aut~entic copies
of papers already published, provided these are duplicated clearly and
bound as an integral part of the thesis. In such instances,
connecting texts are mandatory and supplementary explanatory materiai
ls always necessary.
- Photographs or other materials which do not duplicate weIl must be
included in their original forme
- While the inclusion of manuscripts co-authored by the candidate and
others is acceptable, the candidate is required to make an explicit
statement in the thesis of who contributed to such work and to what
extent, and supervisors must attest to the accuracy of the claims at
the Ph.D. Oral Defense. Since the task of the Examiners is made more
difficult in these cases, it is in the candidate's interest ta make
the responsibilities of authors perfectly clear.
iii
Although aIl the work reported here is the responsibl1ity of the
(
candidate, the project was supervised by Dr. B.E. Coulman, Department
of Plant Science, Macdonald Campus of McGill UniversllY.
manuscripts are co-authored by Dr. B.E. Coulmen.
The three
For consistency and
convenience, aIl manuscripts follow the same format.
The copies that
will be sent to the respective journals, however, will follow the
requirements of each journal.
The first manuscript has been accepted
by the Canadian Journal of Plant Science and will be published in its
July 1991 issue. The second and third manuscripts are being submitted
to the Euphytica and Forage Notes, respectively.
(
iv
ABSTRACT
Jean-Marc Montpetit
Plant Science
INHERITANCK AND AGRONOMIC SIGNIPICANCK OP ADVENTITIOUS ROOT
DEVELOPMENT IN RED CLOVER (Trifol1ulll pratense L.).
Adventitious root growth from the crown of red clover constltutes
a major portion of the root system
i~
older stands.
Two 2 yr old
production fields and 3 yr old research plots were sampled in springs
of 1988 and 1989 to determine the re1ationship between spring vigor
and two root types of red clover.
A higher average
spri~g
vigor
rating was generally associated with the presence of weIl developed
adventitious roots.
Five hundred and fifty six red c10ver plants were dug ln the fall
of 1988 from a space planted (1 X 1 m centers) nursery establlshed in
the spring of the same year.
Two divergent populations of 55 clones
each were produced based on either a low or high score for
adventitious root growth.
The progeny of 32 single-crosses made
within and between the two populations was evaluated for flowerlng
habit and root types under spaced p1anting conditions during the 1989
growing season.
Early flowering individuals were found to have a
significantly lower proportion of adventitious roots than the late
flowering types.
Progeny of the high root crosses had significantly
larger crowns and higher adventitious root scores than progen1es of
the intermediate or low root crosses.
A narrow-sense heritability
estimate of 0.30 was found for adventitious root scores.
Six red clover cultivars were established in solid seedings to
monit-~
adventltious root growth at three sampling dates.
The ratio
of adventitious root volume to total root volume increased from 0.05
to 0.15 over the two growing seasons.
v
RESDHE
VALEUIl AGRONOMIQUE ET TRANSMISSION DES RACINES ADVENTIVES CHEZ LB
TREFLE ROUGE (Trifoliua pratense L.).
Les vieux peuplements de trêfle rouge se distinguent par une
majorité d' indi vidus dont le systême racinaire est principalement
composé de racines adventives émanant du collet.
Deux champs de
trèfle rouge qui amorçaient leur troisième année de végétation Qnt été
échantillonnés. aux printemps 1988 et 1989, afin d'établir une
relation entre la vigueur de croissance printanière et deux types de
développement rac1naire.
Un classement élevé pour la vigueur
printaniire était généralement accompagné de la présence de racines
adventives bien développées.
Cinq-cent-cinquante-six plants de trêfle rouge repiqués au
printemps 1988, suivant un espacement d'un mètre (centre à centre)
dans les deux directions, ont été excavés à l'automne de la même
année.
Deux groupes de 5S individus chacun ont été formés à la suite
d'une sélection phénotypique bidirectionnelle axée sur la production
de racines adventives.
Trente-deux croisements simples ont été
effectués entre individus du même groupe et entre les deux groupes.
Les trois groupes de progénitures ont produit des différences
sinificatives pour l'expression de la floraison, mesurée en jillet
1989, et pour le niveau de production de racines adventives, évalué en
septembre de la même année. Une corrélation inverse a été notée entre
l'expression de la floraison et la production de racines adventives au
niveau du collet.
Les sujets issus d'! croisements entre individus à
forte production de racines adventives ont obtenu un classement
(
racinaire plus élevé que ceux issus des deux autres types de
"
vi
croisemeuts.
.'
Une réponse indirecte à la sélection a été observée
pour le diamatre du collet.
L'héritabilité au sens
~troit
pour le
niveau de production de racines adventives a été évalué à 0.30.
Six cultivars de trèfle rouge ont été semés dans le but de suivre
leur développement racinaire sur deux saisons de croissance.
Le
rapport entre le volume de racines adventives et le volume total de
racines est passé de 0.05, à l'automne 1988, à 0.15, à l'automne 1989.
vU
-~
ACDOVLKDCJr..JŒ1l'l'S
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The author wishes to thank Dr. Bruce E. Coulman for revlewing the
manuscripts and thesis, and for his guidance and encouragement
throughout this projeet.
Lods Researeh
Cent~e
l would l1ke to thank the staff at the E. A.
and, particularly, Wendy Asbil for their help
with the field work and for making some of the equipment available
outside the normal work hours.
l am a1so thankful to André Levae, St-
Clet, Quebee, for allowing the sampling of red elover plants from his
fields.
l am indebted to Dr. Don Smith and Dr. Diane Mather for
reviewtng the first and second manuscripts, respectively.
The advlce
from Dr. Mamdouh Fanous on statistical analysis was also greatly
appreciated.
Special thanks go to Helen Cohen for her help with
photographie material and for encouraging me to undertake this
project.
The support and
~ncouragement
from Carole Portelance, Yves
Leclerc and other fellow gradua te students was greatly appreciated.
The scholarship from the Natural Science and Engineering Research
Coudl of Canada 1s gratefully acknowlegded.
l would like to thank
my employer, Pioneer Hi-Bred Ltd., for allowing me to pursue this
research while at their employ.
Finally, l would like to thank my parents, Yvon and Marguerite,
for their help in some of the manipulations and for their continuous
support during the course of this study.
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viii
TABLE OF CONTENTS
Page
FOREWORD ••••••••..•.••...•••..•.•••.•.••.••••.....•••..••• , .. i Il
ABSTRACT .................... , .. .. .. .. .. • .. .. . .. .. .. .. .. .. . .. . . .. • .. .. . • . . . . . . . . .. .. .. . • ... v
RESU'ME .. .. .. .. .. .. .. • .. .. .. .. .. .. .. .. .. .. .. .. • .. .. .. .. .. • .. .. .. .. .. .. .. .. .. .. .. • .. • • • • • • .. • • • • • • ... vI
ACKNOWLEDGEMENTS.. • .. .. .. • .. • • • • .. .. • • • • • • • • • • • • • • • . . . • • • . • . . • • • . . . • vil i
LIST OF TABLES.................................................................. xlii
LIST OF FIGURES...................................................... xvi 1
INTRODUCTION. .. .. • • • • • • .. .. • • .. .. .. • . • • .. • .. • • . . . • .. • • • . • . • .. • . . . • .. .. • . .... l
1. LITERATURE REVIEW" ........................
10
•
•
•
•
•
..
•
•
•
•
•
•
•
•
•
•
•
..
•
•
•
••
3
Persistence in red clover •••••••.•••.•••.•••...•..••.•.. 3
Factors affecting persistence •.••••.•.•..••.•••.... 3
Root and crown rots ................................. .
Internal breakdown ................................ . 4
Genette variation for tolerance to crown and
root rots ....................
0
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
••
5
Growth types............................................ 5
Description and measurements....................... 5
Relatlonship between growth types, yield and
persistence .......... "' ............................. 9
lnheri tance of growth types........................ 11
Root studles in red clover and related forage legumes .•• 12
Introduction on root and shoot functions •••••••••.. 12
.'
5011 envlronment and root distribution ••••••••••.•. 13
Root types and root classification ••••••••••••••••• 14
lx
III
Red claver roota................................... 15
(
Sl1mpling methods ..........................••....••. 16
Root parameters .................................... 17
Effeet of root type on persistence...............
18
Genetie variation for root characters...........
21
Corre la tion among root and shoot characters.....
23
Estimation of narrow-sense heritability ••••••••••••••••• 24
Diallel cross •.•••.•••••.••••.••••••••••••••••••••• 24
Analysie of genetic
varia~ces ••••••••••••••••••••••
25
Parent-offspring regressions ••••••••••••••••••••••• 26
Realized heritability ••.••••••.•••••••••••••••••••• 27
II.
RELATIONSHIP BETWEEN SPRING VIGOR AND THE PRESENCE OF
ADVENTITIOUS ROOT IN ESTABLISHED STANDS OF RED CLOVER
(Trifollum pratense L.) •••••••••••••••••••••••••••••••••••••• 29
INTRODUCTION. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 29
MATERIALS AND METHODS................................... 30
Sampling of production fields •••••••••••••••••••••• 30
Sampling of research plots......................... 31
Statistical analyses ••••••••••••••••••••••••••••••• 32
RESULTS. • . • • • • . • • . . • • • • • • • • • • . . • • • • • • • • • • • • • • • • • • • • • • • •• 33
Production fields •••••••••••
·..................... . 33
Research plots ••••••••••••••••••••••••••••••••••••• 33
DISCUSSION. . • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 40
·........... " ......... . 42
CONNECTING TEXT •••••••••••••••••• ·..................... . 44
REFERENCES ..••••.•••.••••••••••••
III.
(
RESPONSE TO DIVERGENT SELECTION FOR ADVENTITIOUS ROOT
GROWTH IN RED CLOVER (Trifolium pratense L.) ••••••••••••••••• 45
INTRODUCTION. • • • • . • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 45
x
i
MATERIALS AND METHODS................................... 47
Selection .........................................
•
,I.
47
Greenhouse crosses ••••••••••••••••.......•......... 49
Progeny evaluation .••••...•.•••••.•.•••.••.•..•••.. 49
Statistical procedures •••••••••••.•••••••.••••••••• 50
Computation of heritability estimates •.•••••••••••. 50
RESULTS AND DISCUSSION ••••••••.••.••••••••..•••••••••••• 51
Relationship between root and shoot characters ••••• 51
Root and shoot biomass and correlations •••••.• 51
Growth types ...............
e- • • •
Effect of selection for adventitious
• • •
•
•
•
r~ot
• • • •
•
•
• ••
54
score •••• 59
Variation in metric characters among crosses
and cross types ••••.•••••••••••••••••••••••••• 59
Variation in scores among crosses and
crosstypes ................................................. 61
Heritabiliyof the adventitious root trait •••• 61
Conclusions.. . .. . . . . . . . .. . . . . . . . . . . . . . . . . . .. .. . . . . . . . . .... 64
REFERENCES.. .. • . • • • .. .. .. .. .. • • • • • .. .. . .. .. .. .. • .. .. • . .. .. .. .. • • • • • • • • • • • •• 67
CONNECTING TEXT........................................... 70
VI.
THE DEVELOPMENT OF ADVENTITIOUS ROOTS IN SOLID SEEDINGS
OF RED CLOVER (Trifolium pratense L.) OVER TWO GROWING
SEASONS • • • • • • • • • • • • • • • • • • • . • • • • • . • . • • • • . • • . • . • • • . • . • . . . • . • • ... 71
INTRODUCTION. • • • • • • • • • • • • • • . • • • • • • • . • • . . . . • . • • • • . • • • • • •• 71
MATERIALS AND METHODS................................... 71
Statistical analyses ••••••••••••••••••••••••••••••• 73
RESULTS AND DISCUSSION ••••••••••••••••••.••••••••••••••• 73
Multiple correlations between shoot and root
variables and plant population ••••••••••••••••••••• 75
xi
Effect of stand age on the proportion of
adventitious roots ••••••••••••••••••••••••••••••••• 78
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CONCLUSIONS. • • . . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 78
REFERENCES. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 80
V.
GENERAL DISCUSSION AND CONCLUSIONS ••••••••••••••••••••••• 81
REFERENCES. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 86
APPENDIX A. DETAILED ANALYSES OF VARIANCE FOR THE FIRST
MA.NUSCRIPT. • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 96
APPENDIX B. n.LUSTRATIONS OF ROOT AND GROWTH TYPE RATINGS,
DETAILED ANAL\SES OF VARIANCE AND DATA NOT PRESENTED IN
THE SECOND MANUSCRIPT........................................ 99
APPENDIX C. DETAILED ANALYSES OF VARIANCE FOR
Ta~
THIRD
MA.NUSCRI PT. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 111
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xii
r
LIST OP TABLES
'.
Page
1. LITERATURE REVIEW
Table 1. External root traits studied in alfalfa and
clovers ..............................
Il
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
••
19
II. RELATIONSHIP BETWEEN SPRING VIGOR AND THE PRESENCE OF
ADVENTITIOUS ROOTS IN ESTABLISHED STANDS OF RED CLOVER
(Trifolium pratense L.).
Table 1. Mean spring vigor scores for adventitious root
type of red clover in 1988 and 1989, and correlation
between adventitious root and spring vigor scores ••••••••• 34
Table 2. Mean spring vigor Gcore of red clover plants
in respective adventitious aud taproot classes entering
their fourth growing season (May 1985 seeding, 1988
harvest) ..........•....................................... 35
Table 3. Mean fo1iage weight and ratio of adventitious
root volume to total root volume for taproot scores of
red clover plants seeded in May 1985 and examined in
May 1988 •••••••••••••••••.•••••••••••••••••••.•••••••••••• 37
Table 4. Adventitious root score, mean foliage weight
and ratio of adventitious root volume to total root
volume of respective scores of adventitious roots of
red clover plants seeded in May 1985 and examined in
May of 1988 ••••••••••••••••••••••••••••••••••••••••••••••• 38
Table 5. Spearman rank correlation coefficients among
the variables measured in a red clover root
experiment, May 1988 sampling ••••••••••••••..••••••••••••• 39
III. RESPONSE TO DIVERGENT SELECTION FOR ADVENTITIOUS ROOT
GROWTH IN RED CLOVER (Trifolium pratense L.).
Table 1. Average foliage weight, crown diameter and
root volumes for 1988 and 1989 harvests ••••••••••••••••••• 53
Table 2. Spearman rank correlations between shoot and
root variables recorded in fa11 of 1988 (n-146) ••••••••••• 55
Table 3. Spearman rank correlations between shoot and
root variables recorded in fal1 of 1989 (n-575) ••••••••••• 56
Table 4. Effect of growth types on the average score of
adventitious root (1988) and on the ratio of adventitious root to total root volume (1988 and 1989) •••••••••• 58
xiii
Table 5. Mean adventitious root scores and volumes and
mean crown diameter for the three tYges of single-cross
progeny based on mid-parent root score •••••••••••••••••••• 60
Table 6. Analysis of variance of the adventitious root
score of 78 ha1f-sib families of red claver evaluated
in the fall of 1988 under spaced plantings •••••••••••••••• 65
VI. THE DEVELOPKENT OF ADVENTITIOUS ROOTS Hl SOLID
SEEDINGS OF RED CLOVER (Trifolium pratense L.) OVER TWO
GROWING SEASONS •••••••••••••••••••••••••••••••••••••••••••
Table 1. Stand density (plants m- 2 ) at three sampling
dates of six cultivars seeded in May of 1988 •••••••••••••• 74
Table 2. Multiple correlations for root and shoot
variables in a solid seeding of red clover established
in May 1988 and sampled in the fall of 1988, sprlng of
1989 and fall of 1989 ••••••••••••••••••••••••••••••••••••• 76
Table 3. Effect of tlme (date of sampling) on the
volume of adventltlous roots and on the ratio of
adventltious root ta total root volume in red claver
stand establlshed ln May of 1988 •••••••••••••••••••••••••• 79
APPENDIX A. DETAILED ANALYSES OF VARIANCE FOR THE FIRST
HANUSCRIPT.
Table 1. A.O.V. for fresh welght of feliage, Hay 1988:
effect of repllcates and taproot scores ••••••••••••••••••• 97
Table 2. A.O.V. for fresh weight of follage, May 1988:
effect of repllcates and adventltlous root scores ••••••••• 97
Table 3. A.O.V. for the ratio of adventitious root to
total root volume, May, 1988: effect of rep1icates and
and taproot scores •••••••••••••••••••••••••••••••••••••••• 98
Table 1. A.O.V. for tbe ratio of adventitious root to
total root volume, May, 1988: effect of replicates and
and adventltious root scores •••••••••••••••••••••••••••••• 98
APPENDIX B. ILLUSTRATIONS OF ROOT AND GROWTH TYPE RATINGS,
DETAILED ANALYSES OF VARIANCE AND DATA NOT PRESENTED IN
THE SECOND HANUSCRIPT.
Table 1. Cbaracterlstics of the 44 parents used ln ch~
32 single-crosses made in the winter of 1988-89 ••••••••••• 104
Table 2. Characteristics of the 32 single-cross
progenies established under spaced plantings in May of
1989 and evaluated in September of 1989 ••••••••••••••••••• 105
Table 3. A.O.V. for volume of adventltious roots (cm3 ):
effect of the 32 single ~ross progenies, fa Il of 1989 ••••• 106
xiv
Table 4. A.O.V. for taproot volume (cm3 ): effect of the
32 single cross progenies, fall of 1989 ••••••••••••••••••• 106
Table 5. A.O.V. for total root volume (cm 3 ): effect of
the 32 single cross progenies, fal1 1989 •..•.•••.•.••••••• 107
Table 6. A.O.V. for fresh weight of fo1iage (g): effect
of the 32 single-cross progenies, fallof 1989 •••••••.•••• 107
Table 7. A.O.V. for crown diameter (cm): effect of the
32 single cross progenies, fa11 of 1989 •••••.••••••••••••• 108
Table 8. A.O.V. for volume of adventitious roots (cm 3):
effect of the three cross types, fall of 1989 ••.•••••••••• 108
Table 9. A.O.V. for taproot volume (cm3 ): effect of the
three cross types, fall of 1989 ••••••••••••••••••••••••••• 109
Table 10. A.O.V. for total root volume (cm 3 ): effect of
the three cross types, fall of 1989 ••••••••••••••••••••••• 109
Table Il. A.O.V. for fresh weight of foliage (g):
effect of the three cross types, fall of 1989 ••••••••••••• 110
Table 12. A.O.V. for crown diameter (cm): effect of the
three cross types, fall of 1989 ••••••••••••••••••••••••••• 110
APPENDIX C. DETAILED ANALYSES OF VARIANCE FOR THE THIRD
MANUSCRIPT.
Table 1. A.O.V. for stand densily (plants m- 2 ) at the
first sampling date (10/27/1988): Effect of replicates
and cultivars ............................................. 112
Table 2. A.O.V. for stand density (plants m- 2 ) at the
second sampling date (05-09-1989): Effect of repli ca tes
and cultivars ...•......................................... 112
Table 3. A.O.V. for stand density (plants m-- 2 ) at the
third sampling date (09/09/1989): Effect of replicates
and cultivars •..•......................................... 113
Table 4. A.O.V. for stand density (plants m- 2 ): Effect
of replicates, cultivars and dates •••••••••••••••••••••••• 113
Table 5. A.O.V. for volume of adventitious roots (cm3 ):
effect of replicates, cultivars and dates ••••••••••••••••• 114
Table 6. A.O.V. for volume of taproot (cm3 ): effect of
replicates, cul ti vars and da tes. • • • • • • • • • • • • • • • • • • • • • • • • •• 115
Table 7. A.O.V. for total root volume (cm 3 ): effect of
replicates, cultivars and dates ••••••••••••••••••••••••••• 116
xv
,
1
(
Tab~e
8. A.O.V. for ratio of a~ventitious root volume
(cm) to total root volume (cm ): effect of replicates,
cultivars and dates ••••••••••••••••••••••••••••••••••••••• 117
(
xvi
,.
LIST OF FIGURES
Page
III. RESPONSE TO DIVERGENT SELECTION FOR ADVENTITIOUS ROOT
GROWTH IN RED CLOVER (Trifolium pratense L.).
Figure 1. Frequency distribution of the adventitious
root score of three types of single-cross progenies
evaluated in Fall of 1989. A. Distribution of progeny
where both parents had an adventitious root score of O.
B. Distribution of progeny where one parent had an
adventitious root score of 0 and one parent had a score
~f 4.
C. Distribution of progeny where both parents
had an adventitious root score of 4. Root scores: O-no
adventitious roots, 4=profuse adventitious roots ••••.••••• 62
APPENDIX B. ILLUSTRATIONS OF ROOT AND GROWTH TYPE RATINGS,
DETAILED ANALYSES OF VARIANCE AND DATA NOT PRESENTED IN
THE SECOND MANUSCRIPT.
Figure 1. Variation in adventitious root score for the
one-season old single-cross progeny grown under spaced
plantings and examined in the fa1l of 1989. A. Root
score-O; no adventitious root growth from the crown. B.
Root score~l; sparse adventitious root growth from the
crown and lower stems. C. Root score=2; severa1
adventitious roots growing from the crown and 10wer
stems. D. Root-3; Numerous adventitious roots growing
from the crown and lower stems. E. Root score m 4;
Profuse adventitious root growth from the crowu and
lower stems. F. Comparing extremes in root score;
root score a 4 (left), root score=O (right) •••••.••••.•••••• 100
Figure 2. Growth types of individual red clover plants
transplanted in the field on June 9, 1988 and evaluated
on August 5, 1988. A. Growth type-O; rosette on1y. B.
Growth type-li one to several elongated stems. C.
Growth type-2; a few stems flowering. D. Growth
type-3; many flowering stems. E. Growth type-4j aIl
stems elongated and flowering and little vegetative
growth in the center. F. Spaced-plant nursery at the
time of growth type eva1uation •••••••••••••••••••••••••••• 102
xvii
l
INTRODUCTION
Red clover (Trifolium pratense L.) ls one of the major forage
legume crops ln a number of dairy produclng countries in the north
temperate zone.
Classifled as a short-lived perennial, most of its
yield occurs in the second year of growth (Smith et al, 1981).
Red
clover will tolerate lower pH and more poorly drained conditions than
alfalfa (Medicago sativa L.) (Fairey, 1985).
On the other hand, the
lack of persistence of red clover has often led farmers to consider
other forage legume specles.
With improved persistence, red clover would undoubtedly become a
forage 1egume of choice.
Its potential for better persistence has
already been demonstrated (Gasser afid Gagnon, 1976; Gagnon, 1979),
however, longevlty is greatly shortened under field conditions.
The
different causes of lack of persistence ln red clover have been the
subject of several investigations (Fulton and Hanson, 1960; Graham et
al, 1960; Newton and Graham, 1960; Cressman, 1967; Lambert, 1986).
With a better knowledge of these causes, red clover persistence could
be improved through better management practices and crop improvement.
Breeding for improved persistence in red clover may be achleved by
selecting for overall plant health or by selecting for specifie
desirab1e characters affecting 10ngevity such as growth type in the
year of establishment (Bird, 1948).
Research work on root systems of
red clover and other crops Indicates that secondary root growth may
provide better persistence (Cressman, 1967; Perfect et al, 1987).
Being associated with the longer persisting genotypes, the presence of
adventitious root growth in red clover may thus be considered
beneficia1.
•
Because of the variable nature of root traits, limited
breeding efforts have been made to improve root systems in forage
,
1
legumes (O'Toole and Bland, 1987).
One
not~ble
exception Is the
breeding of creeping-rooted alfalfa (Heinrichs, 1954)
w~ich
resulted
in cultivars with better persistence and drought tolerance.
work (Pederson
~
Previous
al, 1980; Lambert, 1986; Smith, 1988) indlcated the
feasibl1ity of selectlng for root traits in red clover.
Phenotypic correlations among shoot and root characters have been
established for white clover (Trifolium repens L.) and red clover
(Caradus, 1977; Sawai !! al, 1986).
A better knowledge of root-shoot
correlations cao be helpful in selecting for multiple traits.
In a
breeding program, negatively correlated traits would be more difficult
to combine ln the same individuels.
The objectives of this reseerch work were 1) to establish the
relationship between adventitious roots and persistence in red clover,
2) to investigate genotypic variation in root systems of red clover 3)
to correlate root parameters with shoot characteristics, particularly
with growth types and 4) to follow the
roots over two growing seasons.
dev~lopment
of adventitious
3
1. LlTERATOU REVIEV
Perslstence ln Red Clover.
FACTORS AFFECTING PERSISTENCE.
Red clover stands reach maximum
forage yield in the second year of growth (Leath, 1985), thereafter
quickly declinlng to leave a few surviving plants in the fourth and
flfth years (Taylor et al, 1962).
Lack of persistence has been
attributed to diseases (Hanson and Kreitlow, 1953; Fulton and Hanson,
1960; Skipp, 1986), insects (Graham and Newton, 1959) and internai
breakdown, a physiologleal disorder (Graham
~
al, 1960; Cressman,
1967).
ROOT AND CROWN ROTS.
Root and crown rots are known to play a
major role in reducing clover persistence (Hanson and Kreitlow, 1953).
Newton and Graham (1960) reported that an entomological-pathological
complex i8 acting upon red clover longevity.
Successive insect
attacks and disease infections would limit the maintenance of healthy
red clover stands. Root rots have long been associated with poor
persistence of red clover (Fulton and Hanson, 1960).
According to
these authors, first attempts to improve persistence began in the mld
19 th century.
Fusarium spp. are the most common pathogens isolated
from diseased roots.
Westbrooks and Tesar (1955) isolated Fusarium
spp. and Rhlzoctonla solanl from rotted red clover roots.
Some of the
root and crown rot organisms are weak pathogens, invadlng host roots
ooly after mechanical or insect injuries have taken place.
This may
occur soon after seeding and increase in amplitude as the stand
becomes older (Graham
{
~
al, 1960; Newton and Graham, 1960).
Severity
of winters also plays a role in the rate of disease development
(Gagnon, 19i9).
Working with red clover, Gagnon (1979) found that
50 % of the plants acquired root infections in their first winter and
,
r
that no healthy taproots could be found in the third growing season.
Similar resu1ts were obtained with white clover (Westbrooks and Tesar,
1955; Ki1patrick and Dunn, 1961).
There seems to be controversy on the influence of management
practices on the incidence of crown and root rots of clovers.
Gagnon
(1979) found no improvement in root rot incidence by applylng a
cutting schedule conducive to Illgh 1eve1s of carbohydrates in the
roots.
Westbrooks and Tesar (1955) found no difference in root rot
incidence under different ferti1ity 1eve1s and cutting systems.
Pitkanen and Huokuna (1985) showed that different cutting schedu1es
significant1y affected carbohydrate reserves in the roots but
indicated that root diseases had a more profound impact on winter
ki11ing of red
clove~.
On the other hand, Siddiqui
~
al (1968) and
Leath (1985) estab1ished that proper management practices can delay
the onset of root rots.
Coulman and Kielly (1988) found that
management practices (date of seeding and number of cuts in a growing
season) did not repeatedly have the same impact on stand productivity
in the first and second production years.
INttRNAL BREAKDOWN.
In addition to the crown and root rot
complex, internaI breakdown (Cressman, 1967) has a marked effect on
persistence of red clover. No pathogen was consistently associated
with this disorder that ultimate1y causes severe erown deterioration
(Graham
~
al, 1960; Newton and Graham, 1960; Leath, 1985).
This
physio1ogiea1 disorder ls apparently re1ated to the rate of growth as
measured by crown diameter (Leffel and Graham, 1966; Cressman, 1967).
First symptoms May appear three months after seeding (Graham et al,
1960; Cressman, 1967). Management practlces may influence the
5
incidence of this disease (Pratt and Knight, 1983).
Red clover plants
are better able to tolerate crown and root rots and internaI breakdown
when adventltious roots growing from the crown are abundant (Taylor et
al, 1962; Cressman, 1967).
GENETIC
VARIATIOl~
FOR TOLERANCE TO CROWN AND ROOT ROTS.
Genotypic variation for tolerance to crown and root rots, and thus for
persistence, has been reported in red clùver (Gagnon, 1979; Pederson
!!~,
1980; Lambert, 1986).
Gagnon found thf cultivar Hungarapoli to
be the MOSt susceptible to crown and root rots whereas Ottawa was
Intermediate and Dollard and Lakeland were the least susceptible.
Lambert (J986) found no difference in reactlon to Fusarium between the
cultivars Arlington and Florex.
However, Florex genotypes showed a
wider range of responses to Fusarium infections than Arlington.
Bi-
directional selection showed significant differences within progenies
of the Florex population.
Pederson
~
al (1980) found a low
heritability for tolerance to four isolates of Fusarium roseum.
In
addition to disease reslstance, other factors such as maturity (growth
types) and root types (Kendall and Stringer, 1985) are known to
i~teract
with persistence.
Grovtb Types
DESCRIPTION AND HEASUREMENTS.
Early researchers working on red
clover noted differences among strains in maturity and flowering
patterns.
According to Lachance (1956), some early classification of
strains were in three categories: medium red clover (early), Mammoth
red clover (late) and wild red clover.
This classification was
already in use at the turn of the century (Bird, 1948).
l
Several other classifications have been proposed, mostly on the
basis of maturity, growth habit, time and amount of flowering, or
combinations of these criteria.
As stated by Bird (1948) "these
groups differed most widely not only in regards their botanical
characters but a1so ( ..• ) in respect ta their cropping capabilities,
persistence and agronomie characters".
The late types, often known as single eut, are distinctive by
their 'rosette' type of growth in the seeding year. Unless sown very
early in the spring, they do not f10wer in the seeding year and resume
spring growth later the following year than the early types.
also more persistent than the early types (Steppler, 1958).
They are
Ear1y
types, on the other hand, flower profusely in the seeding year but are
not as persistent as the late types (Bird, 1948;
Lacha~ee,
1956).
Depending on the growing location, the early flowering types may yield
two cuts in the first production year whereas the late flowering and
wild types are likely to yield only one eut under the same growing
conditions.
Bird (1948), after Williams (1927), notes that wild
types, although as persistent as late types, are not as productive.
As the red claver stand becomes older, late types can be as productive
as the early types (Williams, 1927).
Although highly variable in
growth habit, wild types flower earlier than early types but produce
little regrowth after cutting.
Other classifications have been put forth in different countr1es
or at different times.
For instance, Russian workers grouped red
clover strains into three classes based on perenniality and rosette
formation (Lisicyn et al, 1935).
Pieters (1928) divided American
strains into eerly and late types which he designated as double cut
red clover and Mammoth red clover respectively.
Hollowell (1940) used
the same classification with further emphasis on absence or presence
---~
7
of pubescence.
Bird (1935) rated strains according to the accepted two classes,
that is, single-eut and double eut red elover.
However, he mentioned
that there was no sharp demarkation between the two classes and that
variation was continuous within a population.
He later proposed five
growth types based on the production of flowering stems and the
deve10pment of a rosette in the seeding year (Bird, 1948).
As noted
in a previous paper (Bird, 1935), maximum differentiation of growth
types is seen ln spaced plantlng in the year of establishement.
Date
of p1anting may also influence the expression of growth types (Smith,
1957).
Bird's five growth type classes, as adapted by Steppler and
Raymond (1954), are as follows:
Type O-Produces rosette only, no flower formation.
Type 1-Produces strong rosette with one or very few
flowering stems, prostrate.
Type 2-Produces fairly prominent rosette with a ring of
flower stems, generally prostrate.
Type 3-Produces indistinct rosette with many flowering
stems, generally upright.
Type 4-Produces no rosette, many sparsely leaved upright
flower stems.
According to the above classification types 0 and 1 are
considered as non-f1owering whereas types 2,3 and 4 are flowering.
Hawkins (1953) presented a somewhat different classification for
the English strains of red clover.
(
His approach takes into account
the time of flowering and the number of internodes on the main
flowering stem to differentiate among strains. A good correlation was
established between the number of internodes and the time of
flowering.
As indieated by the author, the number of internodes per
main stem is a more accurate criterion to distinguish among the
strains.
However, more recent studies indicated that stem length
rather than number of internodes is associated with time of flowering
and hence maturity (Bowley et. al, 1987). These authors pointed out,
however, that the number of internodes ean still be assoeiated with
large differences in flowering types.
In more recent classification schemes, individual components of
red clover have been rated in terms of photoperiodic requirements
(Jones, 1974) and pre-flowering intervals (Bowley
~
al, 1987).
Bowley et al (1987) also showed that shorter day1engths were required
to induce flowering stems than to induce f1owering.
Day1ength
requirements for red clover can be altered by temperature variatiolls
(Aitken, 1964; Leffel and Graham, 1966).
Varying photoperiod can
cause differential growth response in individual red clover plants
(Ludwig
~
al, 1953).
Growth type classification has been used to
d~scribe
red clover
cultivars (Coulman, 1981) and to monitor genetie shifts in seed
production (Steppler and Raymond, 1954; Mclennan
~
al, 1960).
Other
morphological characteristics such as number of flowers, flowering
date and height of flowering stems have been used with limited success
in differentiating red clover cultivars (Pergament and Davis, 1960).
The authors emphasized that several criteria had to be combined to
characterize a cultivar since no single criterion could be used a10ne
to describe a cultivar.
9
RELATIONSHIP BETWEEN GROWTH TYPE, YIELD AND PERSISTENCE.
Yield
and earllness have been associated since the development of cultivated
varieties of red clover (Pieters, 1928; Williams, 1927).
In a same
manner, single eut red clovers are associated wlth increased
persistence (Lissitzyn, 1933; 8ird, 1948).
The above-mentioned
re1ationship between growth type, yield and persistence does not app1y
to wild red clovers (Llssltzyn, 1933).
This author argued that almost
aIl combinations of maturity, persistence and yield occurred in wild
red clovers sampled throughout Russia.
This offers the possibility of
combining desirable traits in the same variety.
Bird (1935, 1948) was among the first to associate poor winter
survival with flowering in the seeding year.
This exp1ains the better
persistence of single cut varieties since they flower sparsely in the
establishment year.
Bird
(lS~8)
indicated that single cut types are
favored by farmers in northern areas, where only one cut ls taken off,
while double cut types are preferred in areas of longer growing season
because of the higher yield.
Therrlen and Smith (1960) evaluated the winter survival of the
five different growth types as defined by 8ird (1948). The effect of
the prevention of flowering on winter surviva1 was a1so investigated.
The treatments included debudding and removal of flowering stems for
various durations.
Their results showed a very close relationship
between flowering types and winter ki11ing, type "0" being the most
resistant and type "4" being the most susceptible to winter in jury.
The age of the red clover plant at the end of the growing season a1so
had an effect on the winter survival abi1ity. Indeed, early seedings
were more damaged than la te ones.
The authors associated these
10
findings to the degree of flowering in the seeding year.
This was
later confirmed by Cressman (1967) who found winter surviva1 to be
inverse1y proportional to growth type rating.
Therrien and Smith (1960) noted that prevention of f10wering,
either through debudding or flower stem removal significantly reduced
winter killing.
In addition, prevention of flowering increased the
number of non-flowering tillers in the fall of the seeding year.
Crown diameter and crown weight were also greater than the control.
Prevention of flowering modified root types toward more branching and,
in some of the treatment.s, higher root weight and higher percentages
of total available carbohydrates (TAC).
To a lesser extent, Smith
(1957) pointed out a similar re1ationship between flowering in first
year and winter killing.
However, flowering plants had heavier roots
and higher levels of TAC than non-flowering plants.
In a later study,
Smith (1963) clear1y eatablished the re1ationship between nonflowering growth types and reduced winter killing.
He even suggested
an indirect selection for persistence on the basis of growth type in
the seeding year.
Prevention of flowering in the seeding ypar through
late seedings did not consistently improve stand persistence (Coulman
and Kielly, 1988).
Similarly, the cutting regime in the first
production year (two cuts versus three cuts) did not have a great
impact on stand productivity or persistence.
Mokhtarzadeh et al
(1967) found that selection for persistence led to a shift toward nonflowering types in the year of establishment.
However, Cou1man and
Oakes (1987) found that selection for persistence ia not always
accompanied by a high proportion of non-flowerlng types in the year of
seeding_
Il
The above discussion does not clearly Indicate whether it 18
(
possible to dissocia te growth type from winter survi ving ability as
suggested by Lissitzyn (1933). Choo (1984) designed an experiment to
de termine if selection for winter survival can be dissociated from
shlfts in growth types.
Correlations were made between growth types
(Bird, 1948), seed yield and winter survival rates.
Results were in
agreement with previous reports (Smith, 1957, 1963; Therrien and
Smith, 1960) as far as flowering response and winter hardiness are
concerned.
As stated by the author toit appears that the correlations
between growth habit and vinter survival holds widely in red clover
varieties at different locations·'.
Moreover, ft was found that highly
productive plants, with good aftermath could be found in similar
proportion both in the flowering and non-flowering classes.
therefore that persistl,mce
~"uld
It seems
be improved by shifting a red clover
population to later growth types without aftecting forage yields
(Coulman, 1981; Choo, 1984).
INHERITANCE OF GROWTH TYPES.
Selection for yield and fas t
regrowth has undoubtedly led to an 1ncrease of flowering types in red
clover cultivars.
Also the practice of taking a hay crop before
producing seed is favoring selection of early types (Steppler and
Raymond, 1954; Mclennan
.!!
al, 1960).
Thus, flowering response in the
year of seeding appears to be under genetic control and not only an
environment effect.
Smurygin.!!. al (1977) found phenotypic
variability for characters such as flowering response, number of
flowering stems and forage yields to
cultivars than in early ones.
{
b~
significantly higher in late
In a later study Smurygin and Kozlov
(1979) found a heritability value of 0.44 for the flowering date using
a late flowering population.
Heritability was close to zero for the
12
same trait in an early flowering population.
In his study on the h\heritance of growth types in red clover
Chiang (1959) conc1uded that growth types were under additive gene
control.
Herttabllity was low, implying that selection for
growth types would not be effective.
Depending on the crosses made.
the estlmated number of gene pairs Involved ranged from 4 to 20.
Results obtained by Mokhtarzadeh
~
al (1967) indicate that i t Is
possible to select for growth types, at least indirectly.
recently, Bowley
.!.!.
More
al (1987) has investigated the heritability of the
pre-flowering interval in two red clover populations.
In one
population heritability varied from 17.2 to 23.2 % dependlng on the
photoperiod treatment.
On the other hand, half-sib families derlved
from a population selected out of Kenstar (cycle 6 of a recurrent
phenotyplc selection for stem length) showed no signifieant variation.
The experimental data suggested a polygenic control of the preflowerlng interva1.
Other workers (Coulman and Oakes, 1987) found
heri tabil1 ty estimates of the growth type character. rather than the
pre-flowering interval, to lie between 52 % and 62 %.
The lack of
consistency of growth type heritability estimates indicates that
different environments or different source populations have an
influence on the selection effectlveness for the trait.
loot studies in red clover and related forage leguaes.
INTRODUCTION ON ROOT AND SHOOT FUNCTIONS.
Although concealed in
the soil, plant roat systems are yield determinants to the same extent
as their aboveground counterparts.
ltoot studies of field crops were
pioneered by J. E. Weaver in the early part of this century.
His book
on the subject, 'Raot Development of Field Crops (1926)' 15 still an
13
often cited reference.
Studies of roots are rendered difficult by the
highly heterogeneous nature of the soU environment (Russell, 1977;
Brown and Scott, 1984; D'Toole and Bland, 1987).
Nonethe1ess, the
possi bUity for genetic improvement of root systems exists and offers
great potential (Throughton and Whittington, 1969; D'Toole and Bland,
1987) •
Root functions are numerous: anchorage of the plant, mineral
nutrition, absorption and conduction, storage of photosynthates,
asexual reproduction etc ••• (Hill et al, 1936).
Therefore, several
root traits cou Id be the object of plant breeding efforts.
Study of
roots can also provide a better understanding of crop behavior and
help propose crop management strategies (Farris, 1934).
SDIL ENVIRONMENT AND RODT DISTRIBUTION.
As mentioned above,
roots display variable growth patterns in response to variable
environments.
For instance, the amount of rainfall or irrigation can
drasticaUy change root distribution.
Russell (1973) in his account
on root development summarized some of the environment effects on root
growth. Dry soUs can increase the rooting depth although prolonged
arid conditions can restrict the root system to shallow depth because
of overaU reduced plant growth.
Pore size and soil strength can
affect the volume of root hairs, the number of laterals and
of the main axis (Russell, 1973; Russell, 1977).
~he
length
Soil texture and
soil structure are known to induce different branching habits in
alfalfa (Weaver, 1920; Carlson, 1925).
In dry clay soils roots may
tend to develop along cracks where seU strength 18 minimal (Rue sell,
1973; Brown and Scott, 1984).
(
Presence of stones and worm holes are
others factors influencing root development (Russell, 1977).
Plant spacing, plant population and thus root competition
14
influence the spread and depth of a root system (Russell, 1973;
Saindon, 1985).
Root distribution and growth may a1so be affected by
soil moisture (Farris, 1934; Mclntosh and Miller. 1981), soi1
temperature (Brar et al, 1990), nutrients and ferti1izers (Ferrant and
Sprague, 1940; Pederson, 1989), herbicide residues (Robertson
~
al,
1985), tillage and management practices (Ferrant and Sprague, 1940),
soil compaction (Upchurch and Lovvorn, 1951; Rechel
~
al, 1990),
aluminum toxicity and strains of rhizobium (Matches, 1988).
Clearly,
the effectiveness of selection for root characters will de pend
directly on maintaining uniform soil conditions to minimize root
variability imposed by the environment.
To tackle the problem of soi1
heterogeneity and lack of spatial independence of root samples,
special statistical analyses and data transformation were developed
(Brown and Scott, 1984; Perfect
~
al, 1987).
ROOT TYPES AND ROOT CLASSIFICATION.
Hill et al (1936) classified
roots on the hasis of their location on the plant (primary roots,
secondary roots and adventitious roots) and on their morphology
(taproot, fi brous root and fleshy roots).
Adventitious roots were
defined as roots originating at unusual places on the plant.
Esau
(1977) classified roots into primary, lateral and adventitious roots,
mentioning that the difference between adventitious roots and laterals
is not always clear-cut.
Cannon (1949) presented an attempt to
classify root systems for crop plants.
He distinguished two root
systems: the primary roots, consisting of roots derived from the
germinating seed, and the adventitious root system developed from
other organs after germination.
The primary root system is always
monoaxial with laterals originating from its pericycle (Cannon, 1949).
lS
The adventitious root system is never simple (no main axis).
Another
distinction made by Cannon (1949) between the two kinds of root
systems Is that adventitlous roots do not have as strong a geotropism
as do the primary roots.
This Buthor also illustrated ten typical
root systems, type four best representing red clover.
RED CLOVER ROOTS.
Fulkerson (1982), in his account on red
clover, estimates that 73 % of root dry
cm of the soil.
m~tter
is found in the upper 20
Slnce the soil environment has a definite influence
it is difficult to generalize on red clover root distribution (Kendall
and Stringer, 1985).
Indeed, Weaver (1926) obtained greater rootlng
depth for red clover than Miller (1916) and Farris (1934).
Differences ln soil types and climate, more specifically in amount of
annual rainfall, were proposed as an explanatlon.
Nevertheless, some
trends in red clover root distribution can be presented.
In short, the red clover root system can be descrlbed as a stout
branched taproot (Spedding and Diekmahns, 1972).
Weaver (1920) also
noted the rapld tapering of the taproot ln three month old red clover
plants and that the taproot still constituted the major part of the
root system at the end of the first growing season.
Fergus and
Hollowell (1960) described red clover underground parts as a taproot
with lateral
root~
originating from the upper portion.
Maximum
rooting depth in mature red clover plants is approximately 1 m (Fergus
and Hollowell, 1960).
Farris (1934) reports that root branching in
red clover is a function of both soil moisture in Juvenile stages and
the red clover strain used.
More recently, Fitter (1986) investigated
the influence of watering rate on red clover roots under controlled
(
conditions.
Branch root initiation was found to take place in
different areas of the roots system under different watering levels:
lb
At low levels, roots were initiated along the main axis whereas under
high watering levels branch initiation was terminal.
Root contractions in red clover may result in sinking of stem
bases in the soil.
As a result, adventitious roots develop at stem
bases and from the crown (Spedding and Diekmahns, 1972).
Because of
the short-lived nature of the taproot, adventitious roots and laterals
often take over the root functions in older red clover plants (Taylor
!! al, 1962; Cressman, 1967; Spedding and Diekmahns, 1972; Kendall and
Stringer, 1985; Sawai
~
al, 1986).
A similar change in the root
system of alsike clover (Trifolium hybridum L.) was observed by
Townsend (1964).
SAMPLING METHODS.
Bohm (1979) gives an excellent review of the
various techniques used for the study of roots.
On1y sampling
techniques applicable to red clover root selection will be covered.
Because of the relatively large numbers of plants examined in a
selection program, sampling needs to be rapid and yet accurate.
Because of time considerations, trench digging, rhizotrons and
monolith methods (Bohm, 1979) are not applicable to a selection
program.
The soil core method is highly suited to obtain volumetric
root samples (Pavlychencko, 1937; Bohm, 1979) but the strength
to drive the core sampler into the soil May be considerable,
especially in clay solls of low moisture or ln stony fields (Schuurman
and Goedewaagen, 1971).
Special equipment may be required to sample
at greater depths or with a large diameter core (Kelley et al, 1947).
Digging a relatively constant volume of solI with a spade proves to be
--
satlsfactory when the root study does not focus on root blomass per
volume of solI (Throughton, 1981).
Digging roots with a spade --the
17
soil block technique (Throughton, 1981 )-- has been used wi th success
(
in the study of the creeping root habi t of alfalfa by extracting
samples of the following sizes: 41 cm X 30 cm (Busch and Davis, 1969)
and 30 cm deep (Mclntosh and Miller, 1981; Perfect
!:!. al, 1987).
Therrien and Smith (1960) a1so used the soil block method for the
study of red clover roots.
1'0 eliminate the prob1em of variable
sample size inherent to the soil block method resu1ts can be
standardized by cutting the taproot to a predetermined 1ength: 5
inches in red clover (Therrien and Smith, 1960) and 20 cm in alfalfa
(Smith, 1951; Perfect et al, 1987).
Electrical capacitance has been used by Ch10upek (1977) to
estimate root size of alfalfa.
However, this gives no indication as
to the type of root or the amount of branching.
Root digging can be facilitated by drawing a tractor-mounted
blade at a constant depth beneath the plants.
The technique was
applied in studies of tomato roots (Stoffella and Volin, 1982) and
aHaHa (Pederson et al, 1984a; Saindon, 1985; Viands, 1988).
ROOT PARAMETERS.
Bëhm (1979) enumerated the most common
parameters recorded in root studies: root number, root weight, root
surface, root volume, root diameter, root length, number of root tips,
shoot: root ratio and rooting depth.
Since roots are quite variable it
i8 considered desirab1e to record more than one parameter at the time
(Bëhm, 1979).
Measurements of root parameter8 can be direct or
indirect (Bohm, 1979) and qualitative or quantitative (Pearson, 1974).
Because they are eastly measured, root weight and root volume are
often used to monitor root growth and root activity.
(
Although more
laborious, measurements of water extraction and root surface are
better indicators of root activity (Car1ey and Watson, 1966; Pearson,
r
"
lS
1974).
On the other hand, good correlations were found between root
surface, root dry weight, root fresh weight and root Iength (Cariey
and Watson, 1966; Wulster, 1985).
Total root length, not to be confused with rooting depth, 15
seldom measured due to the amount of work involved (Throughton, 1981).
Newman (1966) has designed a
metho~
of estimating total root length
based an the total number of root intersections.
The root intersect
method was Iater modified to speed up measurements in experiments
where total root length is needed (Tennant, 1975; Barnett et al,
1987) •
Root penetration and spread have traditionally been assessed by
the c1assicai method of root excavation (Pavlychencko, 1937; Bohm
al, 1977).
~
A more recent technique used herbicide banding at various
distances and depth from the tested plantes) (Robertson et al, 1985).
Plants that produce symptoms of herbicide phytotoxicity must have
reached the herbicide band.
can be appraised.
Hence, root penetration and root spread
This method relies on the assumption that the
herbicide used 18 immobile in the solI.
Special root parameters are often measured in the study of
taprooted forage leg1lmes.
Table 1 summarizes external root parameters
estimated in some important studies on alfalfa and clover roots. Such
root characteristics as branching score (Peder80n
~
al, 1984a), angle
of first lateral with taproot, number and size of laterals and
distance between first lateral with diameter larger than 2 mm and the
crown were aIl thought to contribute to frost heaving resistance
(Mclntosh and Miller, 1981; Perfect et al, 1987).
EFFECT OF ROOT TYPE ON PERSISTENCE.
Although root branching
19
TABLE 1: Externa1 root traits studied in a1fa1fa and c1overs.
(
Parameter
Crop
Root bark area
aHaHa
Brick, 1980; Brick and Barnes,
1982.
Carotenoid pigment
aHaHa
Brick, 1980.
Taproot diameter
aHaHa
Upchurch and Lovvorn, 1951; Leffel
and Graham, 1966; Brick, 1980;
Pederson et al, 1984a; Perfect
et al, 1987;Viands, 1988.
Eva~, 1977; Pederson, 1989.
clovers
(
Reference
Taproot length
alfalfa
Upchurch and Lovvorn, 1951.
white c10ver Caradus, 1977.
Root weight
aHalfa
red clover
Brick, 1980; Mclntosh and Miller,
1980; Pederson et al, 1984a.
Miller, 1916; Kendall and Leath,
1974; Sawai ~ al, 1986.
Root surface
clovers
Evans, 1977.
Total root length
red clover
clovers
aHaHa
Ferrant and Sprague, 1940.
Evans, 1977; Ennos, 1985.
Lamba et al, 1949.
Branching
(number or amount
of laterals)
aHalfa
Fibrous roots
alfalfa
Brick, 1980; Viands, 1988.
white clover Caradus, 1977, 1981.
Adventitious roots
Cressman, 1967; Sawai et al, 1986.
red clover
white clover Ueno and Yoshihara, 1967;Pederson, 1989.
Angle of laterals
with taproot
alfalfa
Garver, 1922; Busch and Davis,
1969; Mclntosh and Miller, 1981;
Perfect !!. al, 1987.
Distance between
first lateral and
crown
alfalfa
Upchurch and Lovvorn, 1951;
Mclntosh and Miller, 1981; Perfect
!!. al, 1987.
Garver, 1922; Smith, 1951; Busch
and Davis, 1969; Mclntosh and
Miller, 1980; Pederson et al,
1984a; Perfect et al, 1981';-Southworth, 1921; Viands, 1988.
red clover
Therrien and Smith, 1960.
white clover Caradus, 1977.
Diameter of laterals alfalfa
Perfect et al, 1987.
...
j
!,
(Perfect
~
al, 1987) and number of secondary roots (Viands, 1988;
Hansen and Viands, 1989) are associated with persistence ln alfalfa
this relationship has not been reported in red clover.
Rdther,
adventltious roots originating from the crown are thought to improve
persistence in red clover (Kendall and Stringer. 1985).
ln fact,
adventitious roots originating from the crown form the major part of
the root system in older stands of red claver (Taylor
~~,
1962;
Cressman, 1967; Spedding and Diekmahns, 1972), alsike claver
(Townsend, 1964) and white clover (Gibson and Trautner, 1965).
Cressman (1967) noted two types of root development in red claver.
One type was predominantly taprooted producing few adventitious roots
or taproots.
This root type easily succumbed to root deterloration.
The other type, taprooted with profuse adventitious roots at the crown
level, remained vigorous in spite of crown and taproot deterioration.
In a study similar to Cressman (1967), Taylor
~
al (1962) suggested
that adventitious roots were proliferated in response to crown and
taproot disintegration.
Terekhova (1956) noted that in the third and
fourth growing seasons Most of the surviving plants had the! r taproots
disintegrated or completely inactive.
Likewise, alsike clover plants
that survived through the second winter relied entirely on
adventitious roots but thelr vigor was then significantly reduced
(Townsend, 1964).
The relationship between adventitious roots and improved
longevity ln red clover is weIl established.
Furthermore, the
negative correlation between the presence of adventltious roots and
growth types (Sawai !:! al, 1986) May explain the better persistence of
non- or late-flowering plants.
Whether the proliferation of
adventitious roots in red clover i9 genetlcally or environmental1y
21
controlled is not clearly defined.
GENETIC VARIATION FOR ROOT CHARACTERS.
Inheritance of root
traits in red clover has not been extensively studied.
(1962) found differences among clones for root types.
Taylor
~
al
Similarly,
Farris (1934) found differences among strains in their rooting
patterns.
For instance, he noted an above average degree of root
branching in a European strain.
In a bi-directional selection
experiment, Smith (1988) succeeded in shifting red clover populations
toward either fibrous root types or mainly taprooted types.
Evidence of genotypic variation for root traits is found in Many
crop species (O'Toole and Bland, 1987).
In general, heritability
estimates have been as high for root characters as for shoot
characters (Throughton and Whittington 1969; O'Toole and Bland, 1987;
Haissig and Riemenschneider; 1988).
Working with white clover,
Caradus (1977) found significant variation among lines for such
characters as amount of fibrous roots, number of taproots and shoot to
root ratio, but not for taproot length nor for the number of primary
1aterals.
However, another experiment showed that selection for root
length in white clover is feasible (Caradus, 1979).
heritability values were 0.44 and 0.33
selections, respectively.
Realized
for the short and high root
Positive correlations were found between
number of taproots and diverse shoot characteristics in white c10ver
(Caradus, 1977, 1981).
A negative correlation was found between
fibrous roots and growth score in white clover (Caradus, 1977).
However, in a later study (Caradus, 1981) root fibrosity was not
different among white clover lines and could not be correlated with
shoot characteristics.
Despite the difficulty of repeating the
r
22
1
results in root studies, several root traits of white clover showed
significant genotypic variation (Caradus, 1990).
Ennos (1985) studied the Inheritance of root length in white
clover.
Genetic control was addittve and narrow sense heritability
estimates were between 0.42 and 0.84.
Phenotypic variation for root
length was continuous and approached a normal distribution.
Root-
shoot correlations were found for certain characters.
More
r~cently,
Woodfield and Caradus (1990) selected for several
root and shoot traits in white claver.
They found a narrow-sense
heritablity value of 0.56 for root dry weight based on parentoffspring regressions.
Perhaps the best example of selection for root traits in forage
legumes is that of creeping rooted alralfa (O'Toole, 1987).
Heinrichs
(1954, 1963) who pioneered the breeding of creeping rooted alfalfa,
found the character to be heritable.
The mode of inheritance was
additive with complementary factors.
Heinrichs and Morley (1962)
estimated the narrow-sense heritability for creeping roots to fall
between 0.20 and 0.26.
They also detected non-additive genotypic
variance in this study.
Smith (1951) was also able ta show that differences among and
within cultivars of alfalfa existed for the creeping root trait.
Although no heritability estimates were computed, Avendano and Davis
(1960) demonstrated that the creeping habit was highly transmissible
to the progeny.
Indeed, crosses between creeplng rooted clones (e X
C) gave a higher number of creeping roots than creeplng by noncreeping (C X Ne) and even more sa than (Ne X Ne).
A few years later, Daday (1962) showed that genettc control of
the creeping root trait ln alfalfa was due to bath additive and
23
(
non-additive gene effects. The magnitude of genet1c variation
Indlcated that selection for creeping roots would be effective.
More
recent studies of creeping rootedness in alfalfa showed that the
expression of this trait i5 subject tu the influence of the
environment, that is, progeny does not always resemble the parents,
depending on the test site (Mclntosh and Miller, 1981) or on the
growing conditions (Pederson et al, 1984b).
Viands (1988) was able to
establish a good correlation among different test sites for alfalfa
root characteristics such as number of secondary roots or fibrous root
masse
Selection for number of secondary roots in alfalfa led to a
significant increase for the trait in the progeny (Viands, 1988;
Hansen and Viands, 1989).
Four populations that wen, through either 3
or 4 cycles of selection for root regeneration capability had on
average 27 % more secondary roots than their unselected counterparts
(Hansen and Viands, 1989).
Carrying out a diallel cross to study the inheritance of root
characters in alfalfa, including root bark composition, Brick and
Barnes (1982) obtained significant GCA effects and non-significant SCA
effects.
Quantitative analysis revealed that the root bark area trait
was controlled by two tetrasomically inherited non-dominant genes.
In view of the above discussion, several root traits of forage
legumes~
including red clover, appear to be under genetic control.
Therefore, further research in the area of red clover root trait
inheritance is warranted.
CORRELATIONS AMONG SHOOT AND ROOT CHARACTERS.
(
Various
correlations have been made between shoot and root traits in alfalfa
(Busch and Davis, 1969; Mclntosh and Miller, 1980; Viands, 1988).
In
24
red clover, the presence of adventitious root has been correlated with
."
growth types (Terekhova, 1956; Therrien and Smith, 1960; Savai et
1986).
!!'
Therrien and Smith (1960) found that the prevention of
flowering in red clover increased root branching and, in sorne
treatments, root weight and percentage of total available
carbohydrates.
Terekhova (1956) noted that taproot diameter was
larger in late flowering types.
This author also reported that
adventitious roots were more abundant in late-flowering types of red
clover.
Sawai et al (1986) classified a red clover population into
five growth types as proposed by Bird (1948).
Root investigations
showed that non-flowering plants (types 0 and 1) had more roots
originating from the crown than flowering plants (types 2, 3 and 4).
These authors also linked the increased amount of adventitious roots
to the better winter survival of late types.
Esti. .tioD of narrov-seDse beritabllity.
The method of estimating narrow-sense heritability in a breeding
experiment will depend largely on the mating system, the type of cross
involved, the selection procedure and the need to Investigate the mode
of inheritance.
Four methods of estimating narrow-sense heritability
are commonly used in forage legume breeding.
They are the diallel
cross analysis, quantitative genetic variance analysis, parentoffspring regression or correlation and realized heritability.
When
root traits are described in a qualitative manner (visual scale) the
analysis of genetic effects should be based on non-parametric
statistics.
DIALLEL CROSS.
The diallel cross has been used ta study the
inheritance of several traits in alfalfa (MacIntosh and Miller, 1981;
Brick and Barnes, 1982; Chloupek, 1982; Pederson et al, 1984b).
A
25
diallel cross analysis can yie1d information on specifie and genera1
combining ability, maternaI effects, dominance effects, and a gives an
estimate of narrow-sense heritability.
The technique consists in
making single crosses in aIl possible combinat ions among a 1imited
number of clones or inbred 1ines.
Reciproca1s and parents are often
included in the progeny evaluation.
Main effects and interactions are
tested in an analysis of variance based on a random or fixed model.
Genetic variances are determined from expected mean squares. Severa1
statistical models for the ana1ysis of dia1le1 crosses are avai1ab1e
(Griffing, 1956; Kempthorne, 1956; Christie
~
al, 1988).
Baker (1978) noted some of the difficulties associated with the
analysis and Interpretation of data from a diallel cross.
Violation
of some of the assumptions associated with the model may lead to
overestimation of the dominance effects.
Qualitative data which may
not follow a normal distribution wou1d pose a problem in testing for
main effects and interactions since the F-test assumes normality.
ANALYSIS OF GENETIC VARIANCES.
Narrow-sense heritability (h 2 )
can also be estimated from a covariance analysls of half-slb or fullsib progenies (Falconer, 1981).
The method consists in comparing the
between-family variance to phenotypic variance (Nguyen and Sleper,
1983).
Based on expected mean squares, the family covariance Is
comput~d permitting the estimation of h2 •
The expected mean squares
will vary whether the model i8 fixed, random or mixed.
Most of the
time the model is considered random, implying that parents were not
under selection (Nguyen and Sleper, 1983).
(
Since half-sib mating i8
commonly used in forage crop breeding, half-sib family covariance
analysls ls often used to estimate herltabillty
b
(Heinrich8 and
26
Morley, 1962; Ennos, 1985; Bowley
~
al, 1987).
Half-sib progeny
covariance analysis gives an estimate of 1 VA (additive genetic
variance) while full-sih progeny analysis gives an estimate of l VA
+ 1 VD (dominance variance) (Falconer, 1981).
Because dominance
effects can impart biases in the estimate of h 2 the covariance
analysis is mostly performed on half-8ib progenies.
Other biases in h 2 estimates may originate from violation of two
assumptions: first, that parents used in generating the half-sth
families are a random sample of the reference population; second,
random interpollinatlon occurred among the parents (Nguyen and Sleper,
1983).
Strictly speaklng the analysis of covariance should not app1y
to non-parametric data.
However, quantitative genetic analyses have
been applied to non-parametric data (scores) (Helnrichs and Morley,
1962; Quesenberry !! al, 1989; Taylor et al, 1989).
PARENT-OFFSPRING REGRESSION.
Narrow-sense heritability can be
estlmated by regresslng offspring (progeny) value on parent value
(Falconer, 1981).
According to Fernando and Gianola (1988) the method
is easy and ls the only one that provides an unbiased estimate of h 2
even when parents have been selected.
Parent offsprlng
regressions/correlations do not yield information on the mode of
inheritance of the trait under study.
If the scale of measurement is
constant for the parents and the progeny then regression of offspring
value on parent value is appropriate (Fernandez and Miller, 1985).
Estimates of h 2 may be affected by genotype X environment interaction.
Frey and Horner (1957) proposed the use of parent-offspring
correlations to overcome scale effects when parents and progeny are
evaluated in different environments.
The correlation coefficient will
equal the regression coefficient on1y when the parent and progeny
27
(
phenotyplc variances are equal (fernandez and Miller, 1985).
Parent-offspring regression can be done with either half-sib or
full-stb progenies.
In the case of full-sib progeny, the linear
regression coefficient gives a direct estimate of narrow-sense
heritability.
For half-sib progenies, the regression coefficient is
multiplied by 2 to estimate narrow-sense heritability.
Heritability
estimates based on parent-offspring regression of full-sib progeny
will include small amounts of dominance effects and dominance type of
epistasis (CasIer, 1982).
Heritability estimates computed from
regression of half-sib progeny on their parents include only additive
genetic variance and additive type of epistasis.
Estimates of h2 based on parent-offspring regression may be
biased upward by the presence of parent-offspring environmental
correlation, dominance and eplstatlc effects (Fernandez and Miller,
1985; Haissig and Riemenschneider, 1988).
To circumvent the problem
of biases in h 2 due to environmental correlation, regression of
progeny mesns from one environment on parent means from another
envirc·nment has been suggested (Casler, 1982).
Shaw (1989) suggested
the use of log transformed data to overcome the problem of differences
in Beale.
In a study on the selection of shoot and root traits in white
clover, heritability estimates derived from either an analysis of
variance of replicated clonaI material or from a parent-offspring
regresslon were found to be closely related (Woodfield and Caradus,
1990; Caradus and Woodfield, 1990).
(
REALIZED HERITABILITY.
A fourth method of estimating
herltabl1lty Is by comparing the selection response to the selection
......
_----------------------------------------~~._......... __ .. .
J
differential (Falconer, 1981). Realized heritability estimates were
found to be similar in magnitude to narrow-sense herltabll1ty
estima tes computed from half-sib family variance ln a red clover
selection for 2,4-0 tolerance (Taylor
~
al, 1989).
Realized
heritability can also be computed in a bi-directional selection
program to see if selection response ls of the same magnitude in both
directions of selection (Caradus, 1979).
ln a bi-directional
selection, the selection differential and selection response can be
computed as the difference between selected and unselected group or as
the difference between the two selected groups.
---,
29
(
II. RELATIONSBIP BETWEEN SPRING VIGOR AND THE PRESENCE OP ADVENTITIOUS
ROOTS IN ESTABLISBED STANDS OP RED CLOVER (Trifoliua prateDse L.).
IHTRODUCTIOH
Lack of persistence in red clover (Trifolium pratense L.) is a
major limitation to the widespread acceptance of this forage legume
by farmers.
Classified as a short-lived perennial, red clover reaches
maximum forage yield in its second year of growth (Lcath, 1985; Smith
~
al, 1985), subsequently declining in vigor and yield as the stand
becomes older.
This decline in vigor has been attributed to diseases,
especially crown and root rots (Fulton and Hanson, 1960), insects
(Graham and Newton, 1959) and internaI breakdown (Graham
~
al, 1960;
Newton and Graham, 1960; Cressman, 1967), a physiological disorder
attacking the crown.
In older stands of red clover, where internaI breakdown and root
and crown rots disintegrated paLts of the crowns and taproots,
surviving plants relied almost entirely on adventitious roots growing
from their crown for support (Cressman, 1967, Spedding and Diekmahns,
1972).
Terekhova (1956) note.d that in the third and fourth growing
seasons most of the surviving red clover plants had their taproot disintegrated or completely inactive.
Taylor
~
al (1962) suggested that
adventitious roots proliferated in response to crown and taproot
disintegration.
On the other hand, Cressman (1967) reported two types
of root development in red clover.
One type was predominantly tap-
rooted, producing few adventitious roots and being more likely to
(
succumb to root rots.
The other type, taprooted with profuse adventi-
tious roots, remained vigorous in spite of crown and root deter-
1
JO
iorations.
It is not clear when adventitious roots occur in the
development of red clover.
One way to Improve the persistence of red clover might be to
promote the growth of adventitious roots either through selection or
management.
However, before taking such steps it is imperative to
establish the relationship between the presence of this root type and
crop persistence.
Thus, the purpose of this research was to examine
the association of adventitious root types with crop persistence,
expressed as spring vigor of individual plants in older red clover
stands.
ItATER.IALS AND MEmODS
S..pling of production fields
The first part of this study was conducted in springs of 1988 and
1989 in swards established from a mixture of common seed of red clover
and timothy (Phleum pratense L.) underseeded to a cereal crop.
These
stands were entering their third year after seeding at the time of
sampling.
The stands were grown separately on a Vaudreuil fine silty
sand on a farm located in St-Clet, Quebec.
Two year old red clover
plants were selected at random and evaluated for spring vigor and the
presence of adventitious rootu.
One hundred and twelve plants were
sampled within an area of approximately 2 ha from April 16 to May 3rd,
1988 for the 1986 seeded field.
One hundred and twenty-five plants
were sampled within an area of approximately 3 ha from April 29 to May
6, 1989 for the 1987 seeded field.
Growth was totally vegetative at
these times, and individual plants were assigned a spring vigor score
where 0 • dead or dying plants and 4 - vigorously growing plants.
same plants were then lifted from the soil with a spade at an
approximate depth of 20 cm, washed in a pail fi11ed with water and
The
31
(
given a visually determined score for the level of development of
adventitious roots growing from their crown on a seale from 0 to 4.
Laterals larger than 2 mm ln
diam~ter
growing from the upper
centIme ter of the taproot at an angle greater than 45 degrees from the
main axis were also considered in this scale.
It was believed that
1aterals close to the crown may play a role similar to adventitious
roots in maintaining plants that had their taproot disintegrated.
The
criteria used to describe laterals growing close to the soil surface
follow a combination of the methods used by Mclntosh and Miller (1980)
and Perfect et al (1987) who studied root branching in alfalfa.
A
score of 0 was glven ta plants that had no root growing from the crown
nor from the upper centimetre of the taproot. Plants that either had a
small number of adventitious roots growing from their crown or at
1east one lateral root (>2mm in diameter) growing from the top
portion of the taproot received an adventitious root score of 1.
A
score of 2 was given to plants with moderate adventitious root growth
from their crown or a minimum of two laterals (>2mm in diameter)
growing from the upper centimeter of the taproot.
A score of 3 was
assigned to plants with profuse adventitious root growth or with more
than two laterals (>2mm in diameter) growing from the top centimeter
of the taproot.
Plants with both profuse adventitious root growth
from their erown and at least 2 laterals (>2mm in diameter) growlng
from the top centimeter of the taproot reeeived a score of 4.
S..plina of research plots
The second part of this study was carried out on a research plot
(
established to study the yield performance of different mixtures of
red clover cv. 'FLOREX' and timothy cv. 'CLIMAX' or cv. 'SALVO' at the
32
E. A. Lods Research Farm, Sainte-Anne de Bellevue, Quebec.
The
experiment was seeded in the spring of 1985, in a randomized complete
black design with three blacks dnd 27 treatments, of which 21
contained red claver in the mixture.
Three red clover plants were
chosen at random within each of the 63 (21 X 3) b10ck-treatment
combinations.
A total of 186 plants (3 missing values) were lifted
from the soil with a spade at an approximate depth of 20 cm between
May 21 and May 25, 1988.
Care was taken ta insert the spade at least
10 cm away from the crown in order to recover most of the root mass.
The main root mass was not severed from the main plant.
Once the soi1
was washed off the root system, roots were cut to u standard 1ength of
15 cm to minimize variability in samp1ing depth.
The fo1lowing data
were recorded from each plant: spring vigor and adventitious root
scores (as described above), taproot size score on an ordinal scale
(O-disintegrated; 1=deteriorated but still visible; 2=deteriorated but
still functional, that is, part of the taproot still had continuous
strands of healthy (not discolored) tissue; 3-functional with some
lesions; 4-intact), fresh weight of top growth, taproot volume and
total root volume.
Adventitious root volume was obtained by
subtracting taproot volume from total root volume.
Root volumes were
determined by water displacement (Burdett, 1979). Root parts were
selectively dipped in a bucket of water held on a top loading scale.
Root volumes were essential1y equal to root fresh weights, e.g. root
volumetric density equaled that of water (data Dot shown).
Statlstlcal analyses
Data from Experiment one were ana1yzed by the Kruskal-Wallis test
for scores using the NPAR1WAY procedure of SAS (SAS Institute, Inc.,
1985).
Differences among root classes for average spring vigor were
33
(
located at the 0.15 experlmentwlse error rate followlng a multiple
comparison procedure described by Daniel (1978).
Spearman rank
correlations were performed on the data.
Non-parametric data obtained from the research plot sampling were
analyzed in a similar manner as for the data obtained from the
production fields.
Quantitative data obtained from the research plots
were submitted to an analysis of variance using a randomized compete
block design.
Differences between means were identified by the
Duncan's multiple range test at the 0.01 level of significance.
RESOLTS
Production fields
Signlflcant differences were observed among root classes for
average spring vigor in the productions fields in both 1988 and 1989
(Table 1).
ln the spring of 1988 only plants with a root score of 4
had a significantly higher average spring vigor.
&owever, differences
among root classes for average spring vigor were more pronounced in
spring of 1989.
Significant correlation coefficients were found
between spring vigor and adventitious root score for data of both
springs (Table 1).
Reaearcb plots
Data from samples taken on the research plots were analyzed to
test the effect of adventitious root and taproot scores on average
spring vigor score.
Significant differences in spring vigor (p<0.01)
were identified for the two types of root classifications (Table 2).
Plants with an adventitious root score of 4 had the highest average
(
spring vigor.
With the exception of type 0, the lower the root score
the lower was the spring vigor.
Although less pronounced, a similar
Table l
Mean spring vigor score for adventitious root type of red c10ver in
1988 and 1989, and correlation between adventitious root and spring
vigor scores.
---------------------------------------------------------------------Average spring vigor
Adventitious
root type
1986 seeding
1988 harvest
o
1987 seeding
1989 harvest
0.90 a
1
1.35 a
1.09 a
2
1.96 a
1. 59 ab
3
2.24 a
2.50
bc
4
3.21 b
3.26
c
Correlation between
adventitious root and
spring vigor scores
0.49
**
0.65
**
Values followed by the same letter within a column are not
significantly different at the 0.15 experimentwise error rate.
l
**
Signifieant at the 0.01 level f0110wing a Spearman Rank
Correlation; n-112 in 1988; n-125 in 1989.
Adventitious root score "0" • no adventitious root growing from the
croWD; adventitious root score "4" - profuse adventitious root growth
from the crown. Spring vigor score "0" - dead or dying; spring vigor
score "4" • healthy. vigorously growing.
35
Table 2
Average spring vigor score of red clover plants in respective
adventitious and taproot classes entering their fourth growing season
(May 1985 seeding, May 1988 harvest).
---------------------------------------------------------------------Adv.
root
score
N
Average spring
vigor score
Tap
root
score
N
Average spring
vigor score
---------------------------------------------------------------------0
98
2.18 ai.
1.00 a
1
15
2.13 a
42
1.81 ab
2
16
2.38 ab
3
50
2.28
3
25
2.68 ab
4
65
3.40
4
32
3.19
0
10
2.30
1
19
2
br.
b
c
Values followed by the same let ter within a column are not
significantly different at the 0.15 experimentwise error rate.
i.
Adventitious root score "0" - no adventitious root growing from
the crown; adventitious root score "4" - profuse adventitious
root growth from the crown. Taproot score "0" • no taproot or
non-functional taproot; taproot score "4" - taproot intact.
(
b
,
36
trend was noticeable with taproot scores, type 4 belng slgnlflcantly
more vigorous than types 0 or l (Table 2).
ln the research plots the majority of the red claver plants
manifested some degree of taproot deterioration.
Over the
1~6
plants
sampled, adventitious roots averaged 86 percent of the total root
volume with 53 percent of the plants having no taproot.
There was
significant variation in spring foliage weight among plants with
different scores for adventitious and/or tap roots (Table 3 and 4).
Plants with a taproot score of 4 produced almost twice the weight of
foliage as those with scores of 0 or l (Table 3).
Plants wlth an
adventitious root score of 4 produced foliage weights more than twice
as hlgh as plants of any other scores (Table 4).
As taproot score
increased to a score of three the ratio of adventitious root to total
root volume generally decreased (Table 3), while the opposite was true
as adventitlous root score increased to a score of three (Table 4).
A significant (p<O.Ol) llnear regression was obse:ved (Y=9.S6 +
1.59 X; r=O.7l) between fresh weight of foliage and adventltlous root
volume.
A significant (p<O.Ol) relationship (Y=20.05 + 2.67 X)
between foliage weight and taproot volume was also observed, although
the coefficient of correlation (r) was quite low (0.38).
Spearman rank correlation coefficients among scores, volumes and
weights measured in the research plot sampling are reported in Table
5.
Correlation between scores and the correspondlng quantitative
measurements were 0.86, 0.79 and 0.93 for sprlng vigor, adventltious
roots and taproots, respectively.
Variables derived from adventitious
roots (score or volume) correlated weIl with top growth measurements
(score or welght).
Taproot score and volume were not highly
correlated with foliage and adventitious root variables.
,
"
37
(
Table 3
)
Mean foliage weight and ratio of adventitious root volume to total
root volume for taproot scores of red clover plants seeded on May 1985
and examined on May 1988.
Taproot
score
Number of
observations
Weight of
foUage (g)
Ratio of adventitious root
volume to total root volume
o
98
19.63 a9
1.000 a
1
15
20.83 a
0.785 b
2
16
28.44 ab
0.766 b
3
25
29.02 ab
0.638 b
4
32
39.41
0.666 b
9
b
9
Values followed by different letters within a column are
significantly different (p(0.05) according to Duncan's Multiple Range
Test.
(
1
38
Table 4
Adventitious root score, mean foliage weight and ratio of adventltious
root volume to total root volume of respective scores of adventltious
roots of red claver plants seeded in May 1985 and examined in May of
1988.
Adventltlous
root score
Number of
observations
Weight of
foliage (g)
RatIo of adventitlous root
volume to total root volume
9
o
10
1
19
8.90 a
0.849 b
2
42
15.73 ab
0.866 b
3
50
19.30
0.904 b
4
65
41.60
e
0.339 a
b
c
0.895 b
Values followed by different letters wlthin a column are
significantly different (p{O.05) according to Duncan's Multiple Range
Test.
39
.
t
Table
~
Spearman rank correlation coefficients among the variables measured in the
red clover root experiment. May 1988 sampUng.
Score of
spring vigor
Taproot
score
Adventi tious
root score
FoUage
welght
Taproot score
0.29
**
AdvenU tious
root score
0.60
**
FoUage we1ght
0.86
**
0.37
**
0.65
Taproot volume
0.30
**
0.93
**
0.02 NS
0.38
**
Adventitious
root volume
0.63
**
0.22
**
0.79
**
0.71
*.
**
-0.02 NS
**
Sign1ficantly different from zero at the 0.01 level.
NS Not signif1cantly different from zero at the 0.05 level.
'1
ft
Taproot
volume
0.24
**
•
40
DISCUSSION
A positive relationship between spring vigor and the presence of
advent itious roots was observed ln red clover product 10n f lelds
entering their third growing season.
A simllar trend was observeà in
research plots entering their four th growing season where bath root
scores and root volumes were positive1y relatt>d to the fresh weight of
top growth.
Plants with no adventitious roots (type "0") did not
produce the lowest spring vigor rating in the research plot sampling.
Any plant that had no adventitious roots and a deteriorated taproot
would have been dead and therefore not included in our sampling.
Therefore, the ten samp1ed plants with no adventitious roots must have
remained aU ve due to functional taproots which either escaped root
rots or had a higher degree of tolerance to the causal organisms.
If wa exclude these plants with an adventi tious root score of "0" from
Table 2, spring vigor increased steadlly wi th larger adventitious root
scores.
Fifty three percent of the plants ln research plots had lost
their taproot whlle the remainder manifested some degree of taproot
deterioration.
This agrees with previous findings
Taylor et al, 1962).
(Cressman, 1967;
Adventitious root score was not related to
taproot score in this experiment (Table 6).
Hovever adventitious root
volume was slightly correlated with taproot volume (r-0.24, p 0.01).
Although small, this correlation agrees with Hansen and Viands (1989)
who found a positive correlation between taproot size and secondary
root development in alfalfa.
The presence of adventitious roots
growing from the crown of red clover May therefore be governed by
taproot size ln addi tion to being proliferated in response to taproot
d1sintegration, as suggested by Taylor
!!.
al (1962).
41
1 n an experiment with alfalfa, Fankhauser and Volenec (1989)
noticed a rapid root growth 6 to 8 months after grafting vigorously
growing shoots (scions) on either low or fast growing rootstocks.
They conc1uded that shoot elongation rate influenced overall plant
growth whereas rootstock growth rate had little effect.
The presence
of this phenomenon in our study may not be significant since spring
vigor was evaluated three to four weeks after red clover plants broke
dormancy.
Since roots and crowns are the overwintering structures of
red clover it can be speculated that the presence of adventitious
roots is the cause rather than the consequence of superior spring
vigor.
The relationship between adventitious roots and spring vigor
was noticeable in both research plots and production fields covering a
perlod extending from late April to late May.
Based on observations of the research reported herein and a
preliminary sampling of a spaced plantjng entering Hs third growing
season (unpublished data) the best time to characterize adventitious
roots in red clover under our climate would probably be in stands
entering their third growing season.
Indeed, younger plants lack
sufficient adventitious root development to show any differences,
whereas older plants rely almost exclusively on thls root type for
support; not many plants without adventitious roots would survive
until the fourth growing season.
Only 5.3 percent of the 4 year old
plants sampled in the research plots had no adventl tious rooU.
The good correlation between visual ratings and quantitative
measurements indicates that a visual scale i8 a good alternative to
if...
measuring weights and volumes when a large number of plants needs to
be characterized such as in a selection program •
42
REPERERCKS
..
BURDETT. A.N. 1979. A non-destructive method for medsuring
of intact plant parts. Cano J. For. Res. 9: 120-122.
th~
volume
CRESSMAN, R.M. 1967. InternaI breakdown and persist:ence of red claver.
Crop Sei. 7:357-361.
DANIEL, W.W. 1978. Applied Nonparametric Statistics. Houghton Mifflin
CO. Boston.
FANKHAUSER, J.J. and VOLENEC, J.J. 1979. Root vs. shoot effects on
herbage regrowth and carbohydrate metabol1sm of aHaHa. Crop
Sei. 29: 735-740.
FULTON, N.D. and HANSON, E.W. 1960. Studies on root: rots of red clover
in Wisconsin. Phytopath. 50:541-550.
GRAHAM, J.H., RHYKERD, C.L. and NEWTON, R.C. 1960.
InternaI breakdown
in crowns of red clover. Plant Dis. Rep. 44: 59-61.
GRAHAM, J.N. and NEWTON, R.C. 1959. Relationship between root feeding
insects and incidence of crown and root rot in red clover. Plant
1>is. Rep. 43:1114-1116.
HANSEN, J.L. and VIANDS, D.R. 1989. Response from phenotypic recurrent
selection for root: regeneration after taproot severing in
alfalfa. Crop Sei. 29:1177-1181.
LEATH, K.T. 1985. General diseases. in N.L. Taylor, ed. Clover science
and technology. Agronomy 25:205-233.
HCINTOSH, M.S. and MILLER, D.A. 1980. Development of root-branching
in t:hree alfalfa cultivars. Crop ScL 20:807-809.
NEWTON, R.C. and GRAHAM, J.H. 1960. Incidence of root feeding weevils,
root rot, internaI breakdown, and viruses and their effect on
longevity of red clover. J. Econ. Ent. 53:865-867.
PERFECT, E., MILLER, R. D. and BURTON, B. 1987. Root: morphology and
vigor effects on winter heaving of established alfalfa. Agron. J.
79: 1061-1067.
SHITH, D., TAYLOR, N.L. and BOWLEY, S.R. 1985. Red clover. in N.L.
Taylor ed. Clover science and techno10gy. Agronomy 25:457-470.
SAS
Institute, Ine. 1985. The NPAR1WAY procedure. pp. 607-614 in SAS
User's Guide: Statistics, Version 5.
SPEDDING, C.R.W. and DIEKMAHNS, E.C. 1972. Grasses and Legumes in
British Agriculture. Bulletin, Commonwealth Bureau of Pastures
and Field Crops, No. 49, pp. 370-386. Farnham Royal:
Commonwealth Agricultural Bureau.
43
(
TEREKHOVA, A.F. 1956. Study of the root system in red clover. Bot. Zh.
SSSR 41:553-558 in SPEDDING, C.R.W. and DIEKMAHNS, E.C. 1972.
Grasses and LeguDH!s in British Agriculture. Bulletin,
Commonwealth Bureau of Pastures and Field Crops, No. 49, pp. 370386. Farnham Royal: Commonwealth Agricultural Bureau.
TAYLOR, N.L., STROUBE, W.H., KENDALL, W.A. AND FERGUS, E.N. 1962.
Variation and relation of clonaI persistence and seed production
in red clover. Crop Sci. 2:303-305.
CODECTIMG TUT
'.
Adventitious root growth from the crowns of red claver plants
undoubtedly plays a role in maintalning plants that have lost cheir
taproot.
If the adventitious root type was under genette control,
this would offer a possibility of developing cultivars with improved
persistence.
The association between flowering types (growth types) and
persistence in red clover was recognized several decades aga.
Late
flowering or nonflowering types (single-cut) are generally more
peristent than early-flowering types (double-eut).
~
The work of Sawai
al (1986) showed a relationship between growth types and
adventitious root production, late- or nonflowering types produeing
more of this root type.
More work was needed to better understand the association between
flowering habit, adventitious root growth and persistence.
An
experiment was thus designed ta look at the heritability of
adventitious roots and their association with growth types under
spaced plantings.
The impact of flowering habit of individual plants
on winter survival was also assessed.
LlTEBATURB CITED
SAWAI, A., GAU, M. and VEDA, S. 1986.
Difference in root system among
growth types of red claver. J. Japan. Grassl. Soc. 32:164-166
45
III. IESPORSB TO DIVERGBRT SELICTIOR rOR ADVENTITIOUS ROOT GROVTR IR
(
IED CLOVER (Trifollua pratense L.).
INTRODUCTION
Many important forage legumes are herbaceous perennials
persisting from one growing season to the next due to their perennial
roots and crowns.
Specifie root traits have been eorrelated with
better persistenee in these erops.
(Perfect
~
In alfalfa, root branehing
al 1987) or ereeping roots (Avendanù and Davis 1966;
Heinrichs and Morley 1960) and number of seeondary roots (Hansen and
Viands 1989) were positively assoeiated with better persistenee.
Adventitious roots originating from the crown are thought to promote
better persistence ln red clover.
Indeed. these adventitious roots
formed the major part of the root system in older stands of red clover
(Spedding and Diekmahns 1972; Cressman 1967; Taylor et, al 1962).
Similar observations were made on white clover (Gibson and Trautner
1965) and alsike clover (Townsend 1964).
A recent experiment showed
that profuse adventitious root growth from red clover crowns imparted
better spring vigor of plants in three and four year old stands
(Hontpetit and Cou Iman 1991, in press).
Evidence of genotypic variation for root traits has been reported
in many crop species (O'Toole and Bland 1987; Throughton and
Whittington 1969) including white clover (Woodfield and Caradus 1990;
Caradus 1981, 1979, 1977) and alfalfa (Viands 1988; Pederson et
1984; Helnrichs and Morley 1960).
!!
ln red clover, strain and clone
differences in rooting patterns have been reported (Taylor
~
al 1962;
Farris 1934) but the inheritance of root traits has not been
(
extensively studied.
Smith (1988) has been successful ln selecting
for root types in red clover.
He was able to shift populations
towards either fibrous root types or mainly taprooted types.
Root and shoot characteristics are often correlated.
ln dlfaIfa,
top growth weight has been found to be positively correlated with root
branching (Mclntosh and Miller 1980), crown and root weight (Bush and
Davis 1969) and taproot diameter (Viands 1988).
In red clover, the
presence of adventitious roots growing from the crown has been found
to be negatively correlated with the amount of flowering of individua1
plants in their seeding year (Sawai
1960; Terekhova 1956).
~
al 1986; Therrien and Smith
Bird (1948) proposed a five-unit scale to
describe the degree of flowerlng of individual plants grown ln spaced
plantings in their seeding year.
Type 0 and 1 were non-flowering
whereas types 2 to 4 had an increasing degree of flowering in the
seeding year.
Non-flowering or late-flowering types were more
persistent then profusely flowering genotypes (Choo 1984; Smith 1963;
Bird 1948).
Sawai et al (1986) attrlbuted the better persistence of
non-flowering and late-flowering ramets to their ability to produce
more adventitinus roots from their crown.
The larger crowns of non-
flowering types (rherrien and Smith 1960; Smith 1957) would provide
more buds or sites for adventitious root growth (Sawai et al 1986).
Lack of persistence of red clover is a major obstacle to its
widespread use as a forage crop.
Red clover populations with improved
adventitious root growth would be expected to have improved
persistence (Cressman 1967).
Therefore, one objective of this study
was to estimate the heritability of adventitious root production and
de termine the potential for selection for this trait.
An additional
objective was to evaluate correlations among root and shoot characters
with particular attention to the association of growth types with
- l
47
adventltlous roots.
(
The re1ationships between visual scores and their
quantitative (parametric) measurements was a1so investigated.
HATERIALS AND METHODS
Selection
The experiment was conducted on the progenies (5yn 1) derived
from seven p01ycrosses each composed of 10 to 12 clones.
clones involved vere selected from
CyS
The 78
ARLINGTON and FLOREX, in equal
proportions, on the basis of their flowering ability (growth type) in
the seeding year.
On April 1 1988, 24 germinated seeds (hypocotyl-2-3
cm) from each of the 78 clones were sown in 96-ce1l flats.
Seedlings
were kept in the greenhouse and drench inocu1ated with a rhizobiumpeat suspension at the 2-3 1eaf stage.
On June 9 1988, seedlings were
transplanted on one-meter centers in the field on a Sainte-Rosalie
clay 10am.
The field layout was a randomized complete block design
with three replicates and five plants (sampling units) per replicate.
The 1170 red claver plants were irrigated dally for a period of two
weeks after transplanting due to very dry conditions.
A diazinon
drench was applied in early August to reduce white grub (Phyllophaga
spp.) feeding on red clover roots.
On Augus t 5, 1988, growth types were recorded on a visual scale
from 0 to 4 (O-non floweringj 4-profusely flowering) according to
5teppler and Raymond (1954).
types vere recorded.
Plants were clipped once after growth
Approximately half of the plants were sampled at
random (154, 162 and 169 for replicates 1,2 and 3, respectively) and
harvested between September 25 and October 8 1988 with each repUcate
(
taking from 2 to 4 days.
Plants were excavated with a spade at an
approximate depth of 15-20 cm, a procedure referred to as the soil
48
block method (Bijhm 1979).
masse
Care was taken to reeover the maIn root
Plants remaining in the field were allowed to overwinter ta
verify the relationship between growth type and winter survival.
The
following spring. these plants were rated for spring vigor on a seale
from 0 to 4 (O=dead or dying;
4~healthy
with abundant sprlng growth).
Roots of harvested plants were washed in water and eut at a
standard length of 15 cm to minimize variation in sampling depth.
Visual scores from 0 to 4 were used ta describe adventitious root
growth (Oano adventitlous root growing from the crownj 4 a profuse
adventltious roots) and taproot growth (O-Several to Many taproots
with a small dlameterj 4=one or few prominent large taproots).
Taproot and total root volumes were measured uslng the Archimede's
prineiple of water
displaeem~nt
(Burdett 1979).
This non-destructive
method of measuring roots allowed us to keep plants alive for later
crossing purposes.
For one of the repllcates, taproot volume was
measured by selectively dipping this root part in a bucket of water
placed on a top loading scale.
Selective dipping of taproots was too
time consuming to be conducted for aIl replicates wlthln the available
time for harvest.
Completion of harvest within a short tlme perlod
was critical as red clover grows very rapldly in late September.
For
the first repllcate. adventitlous root volume was found by subtractlng
taproot volume from total root volume.
Only total root volume was
measured for replicates two and three.
Root weights and volumes were
very closely related (r=0.98) (data not shown).
For practlca1
purposes. root volume (in cm 3 ) and root fresh welght (ln g) could be
.ft.
-.'
considered to be equal.
Whole plant fresh weight was measured
directly while fresh weight of foliage was found by subtractlng total
49
(
root volume from total plant weight.
Crown diameter was measured with
a vernier caliper.
Bi-di~ectional
selection was imposed to obtain two populations of
55 clones each of low (0) and high (4) adventitious root scores.
group thus represented a 10 % selection intensity.
Each
The selected
plants with previously washed roots were potted in disinfected soil,
clipped and placed in a greenhouse under a 16 hour photoperiod to
induce flowering.
Greenhoule cro.ses
Thirty-two single-crosses were made as follows:
10 interpopulation crosses, denoted SI, and 22 intrapopulation
crosses, Il crosses in each of the high and low root selections,
denoted 5+ and S-, respectively.
Cross pollination was do ne by the
toothpick method (Taylor 1980) and seeds of reciprocals were kept
separate.
Individual clones were used only once in intrapopulation
crosses although some of them were used a second time in Interpopulation crosses.
Self-pollination of clones indicated that the
frequency of self-compatlbility was less than 0.5 % on average.
Progeu7 eva1uation
Seeds of the 32 single-crosses and thelr reclprocals were pregerminated and sown in cone shaped cells to produce a minimum of 20
seedlings per single-cross.
The 640 seedlings were transplanted on
one-meter cent ers in the field on an Oka light sandy loam on May 24,
1989.
The field layout was a randomized complete black design with 32
treatments (single-cross progenies), 4 replicates and 5 plants per
(
replicate.
Seeds of reciprocals were confounded with the replicates.
For each of the 32 crosses, 10 seeds of one direction of the cross
were assigned to replicates two and three whereas 10 seeds of the
,
i
so
other direction of the cross were assigned to repllcates one and four.
Variables measured and methodology were identica1 ta 1988.
no white grub infestation in 1989; thus no insecticides
Growth types were recorded on July 15, 1989.
twice before harvest (July
~2
There was
w~re
used.
Plants were clipped
and August 22).
Plants were harvested
from September 17 ta September 21 1989, one replicate per day.
Statistieal procedures
Spearman rank correlations were performed among aIl scores and
quantitative measurements.
The effect of growth types on adventitious
root score and spring vigor in the year following transplanting was
analyzed by the Kruskal-Wallis test and by Spearman rank correlations.
The effect of the 32 crosses on the quantitative variables (fresh
weights, root volumes and crown diameter) was analyzed by the GLM
procedure of SàS (SAS Institute 1985).
Friedman's test was used to
evaluate variation in the 32 single-crosses for root scores and growth
types.
Significant differences were located at the 0.15 experiment-
wise error rate according to a multiple comparison procedure that
follows the Friedman's test (Daniel 1978).
A second set of analyses,
similar to those described above, was conducted using the 32 crosses
grouped according to the three mid-parent root scores (S-, SI, and
S+).
Co.putation of heritability estiaates
Two heritability estimates were computed from parent-offspring
regression and from an analysis of half-sib family covariance ln the
parent population.
Mid-parent values of 0, 2 and 4 were used in
computing the parent-offspring regression coefficient of the
adventitious root score.
In the analysis of full-8ib progeny, the
51
(
regression is considered a direct estimator of narrow-sense
heritabllity (Falconer 1981).
The narrow-sense heritability of
ddventitLous roots was also computed from hali-9ib family covariance
analysls of the parent population (Table 6).
A random model for a
randomized complete black design with sampling units was used (Steel
and Tarrie 1980, p. 219).
The parent population underwent selection
for growth types but not for root traits.
Narrow-sense herltabi11ty
(h 2 ) was estimated as 4 X t (Falconer 1981).
RESUL'~S
Mm DISCUSSION
Relationsbip betveen root and sboot cbaraetera
ROOT AND SHOOT BIOHASS AND CORRELATIONS. Due ta insects, diseases
and drought, sample sizes were reduced from 556 ta 485 and from 640 ta
575 observations in 1988 and 1989, respectively.
Although 10.2 % of
the plants died before harvest in 1989, each of the 128 experimental
units had at least one live plant, the average being 4.49 plants per
unit. The method used in this study of starting seedlings in plastic
flats led to the proliferation of several to many
distorting the red claver taproot system.
tapro~ts,
thus
At transplanting time, the
main taproot often started to coil at the bottom of the plastic cell
and lost its apical dominance.
Deeper, narrower cells were used in
1989 but this did not markedly improve this situation.
Few
adventitlous roots had developed from crowns at the time of
transplanting.
Their development and shape were therefore not
affected by the size of the plastic cell.
Rodrigues and Smith (1989)
suggested field sowing of progeny seed to overcome root distortion
encountered with alfalfa transplants.
However, there i8 greater
mortality of seed1ings using this method and our small amount of
52
available seed made this impractlcal.
Mean Coliage weight and root
reported ln Table l.
volum~s
for bath harvest years are
ln 1988, an average tJproot volume of 41.75 ~m3
accounted for 70 % of the total root volume, the remalnder (30 %)
representing the volume of adventitious roots.
In 1989, total root
volume, follage welght and crown diameter were in the same arder of
magnitude as in the previous year.
However, adventitious roots were
comparatively smaller in 1989 slnce taproot volume made up 9S % of
total root volume.
The small adventitlous root volume found in 1989
could be the result of adequate soil moisture in thc carly part of the
summer.
A lighter 80il texture in 1989 may have induced a ditferent
root response.
Siddiqui
~
al (1968) found that clipping twice rather
than once reduced the growth of secondary roots in red clover.
Even
when both harvest years are considered, adventitious roots accounted
for a small portion of the total root system.
This agrees with
previou8 findings (Cressman 1967) where adventitious roots were smalt
in younger stands of red clover but grew larger as the stands became
older.
Most variables were significant1y corre1ated although the
magnitude of coefficients was often smaii (Table 2 and 3).
Moderate
correlation coefficients of 0.59 and 0.65 (p 0.01) were found between
adventitious
r~ot
volume and adventitious root score for the 1988 and
1989 harvests, respectively.
A 0.79 (p 0.01) correlation was found
between adventitious root score and root volume of three year old red
clover plants examined in a previous experiment (Montpetit and Coulman
1991, in press) indicating the higher consistency of measurements when
v
adventitious roots were 1arger.
The difficulty in measuring the
smaller adventltlous root volumes in the present study lead ta more
53
Table 1
Average follage welght, crown dlameter and root volumes for 1988 and
1989 harvests.
Year
l'
1
t
Sample
Taproot
Adventitious
Total root
Fresh welght
Crown
size
volume
(cm)
root volume
(cm))
volume
(cm))
of foUage
diameter
(g)
(cm)
1988
146
29.4
12.4
41.8
335.0
2.29
1989
575
46.5
2.7
49.2
388.2
2.65
S4
variation in the results, possibly explaining the poor correlation of
this root volume with variables other than adventltious root score.
Moderate to high correlations
w~re
found among total root volume,
fresh weight of fo1iage, crown diameter and taproot volume for both
harvest years (Table 2 and 3).
Since taproot volume accounted for
most of the total root volume in 1989, the two variables were highly
correlated (r a O.97; p 0.01) and both had very similar correlations
with other variables.
GROWTH TYPES.
Of the 574 plants left in the field in fall of
1988, 59.6 % died over the winter.
The correlation between growth type
(August 1988) and spring vigor (May 1989) was small and nonsignificant (p 0.05).
Similarly, mean spring vigor was not
signiflcantly different among growth types (p 0.05), even when the
dead plants were excluded from the analysis.
Severe
wi~terkilling
due
to lack of snow cover and ice sheeting could explain the lack of
correlation between growth types and winter survival evaluated as
spring vigor.
Previous studies established an association between
winter survival and non-flowering ramets (Therrien and Smith 1960;
Smith 1963; Mokhtarzadeh
~
al 1967; Choo 1984).
However, Bird (1948)
mentioned that in some years growth types did not aeem to be
correlated with winter survival.
He suggested that such relationships
would have to be tested over several winters to obtain signlficant
correlations.
In 1988, growth types had moderate negative correlations with six
of the seven other variables; the largest abso1ute values, -0.46,
-0.47 and -0.41 being associated with total root volume, foliage
weight and crown diameter, rcspectively.
In 1989, growth types
."~
~
'IlIble 2
SpealIIIIIl tank correlatioœ between shoot and root variables recorded in FaU of 1988 (n-146).
Taproot
score
~.061
Crown dJ.ameter
Fœsh we1ght of fol.iage
0.188
NS
*
AdYentitious Grwth
root score
types
Taproot
volœe
Advent1.t1ous Total root
root volœe volœe
Fresh 1elght
**
0.265 **
0.511
0.281
**
0.163 *
0.706
~.469
**
0.646 **
-0.358
**
**
-0.234 **
~.198
*
0.297
Total root volœe
-{).033 R;
Adventitious root vol\IE
-0.237
**
**
0.593 **
Taproot volœe
0.2œ
*
0.005 NS
Gtœth types
0.~2 R;
Adventitious root score
R; Ncn-s1gnf.ficant
* Significant at
~.1SO
0.382
-{).360
~.413
**
**
-{).459 **
0.671
0.430
**
0.738 **
0.688
of foliage
tir
**
**
NS
at the 0.05 level
the 0.05 level
** Slgn1ficant at the 0.01 l.eve1.
VI
VI
.........
...
~
...
'DIble 3
SpeanIIIIl rank correlations between shoot and root variables recorded in Fall of 1989 (n-575).
Taproot
score
Crown diameter
Fresh we1ght of follage
Total root vol\111e
Adventitious root volUE
Taproot volUE
Growth types
Adventitious root score
~
**
0.375 **
0.166
**
-{).191 **
0.243
**
-{).192 **
-{).1l8 **
0.301
AdveDtitious Gmith
types
root score
0.250
**
-{).301
0.œ5
*
-{).281
**
**
-{).327
**
0.009 •
0.651
**
0.029
R)
-{).023
R;
-{).341
**
0.091
*
Taproot
wl\111e
Adventitious Total root
root wl\111e wl\111e
**
0.583 **
0.967 **
0.231
**
0.025
R)
0.152
**
0.637
-{).026
**
0.585 **
0.682
Fresh weight
of foUage
0.544
**
~
Nœ-s1gn1ficant at the 0.05 leve1
the 0.05 level
Significant at the 0.01 leve1.
* Sign1ficant at
**
..n
57
(
generally had smaller negative correlations with other variables.
The
largest absolute values were found between growth types and total root
weight (-0.33), fresh weight of folidgc (-0.28), crown diameter
(-0.30) and taproot volume (-0.34).
The significant negative correlations between growth types and
six of the seven variables in both harvest years agree with previous
findings (Smith 1957; Therrien and Smith 1960) where non- or lateflowering plants generally had larger rcots, shoots and crowns than
the early flowering types.
Correlations between growth types and
adventitious root score were low (r--0.36, p 0.01, in 1988; r-0.09,
p 0.05, in 1989).
When average adventitious root score was computed
at each of the five growth types signlficant differences (p 0.01) were
noticed in 1988 but not in 1989 (p 0.05).
Significantly smaller mean
adventitious root scores were associated with more profuse flowering
growth types in 1988 (Table 4).
The average ratio of adventitious root to total root volume was
computed for each of the five growth type classes (Table 4).
In 1988,
significantly smaller ratios were found as growth type score
increased, indicating that adventitious roots were proportionally
smaller in size in flowering plants.
difference was found.
In
]~~9,
no significant
The values obtained in this study for the ratio
of adventitious root volume to total root volume approached those
observed by Sawai
~
to total root weight.
al (1986) who compared adventitious root weight
The siml1ar values suggest that the inverse
relatlonshlp between growth type and proportion of adventitious roots
(
Is present in different sources of red clover germplasm.
The lack of
association between the adventltious root to total root ratio in 1989
may lie in Inadequate growth type differentiation due to early
,
Table 4
Effect of growth types on the average score of adventitious roots (1988)
and on the ratio of adventitious root to total root volume (1988 and 1989).
Sample size
Average adventitious
root score
1988
1988
o
20
3.60
1
44
2.57
b
0.408 a
0.051
2
137
2.29
be
0.299 a
0.052
3
216
1.93
0.254 ab
0.053
4
68
1.59
0.107
0.076
Growth
type
Ratio of adventitious
root to total root volume
1988
a
e
1989
0.359 a t
cd
d
b
0.044~
e Means followed by the same let ter are not significantly dlfferent at the
0.15 expe~imentwise error rate aeeording to the multiple eomparlson
procedure that follows the Kruskal-Wallis test.
• Means followed by the same let ter are not significantly different at the
0.05 level according to the Duncan'e multiple range test •
.2
Ratios were not significantly different at the 0.05 level in 1989
following an analysis of variance.
l
59
(
transplanting.
Smith (1957) noted that late sprlng (June)
transplanting produced maximum dlversity in growth types of individual
plants.
However, the risk of a mldsummer drought as experienced in
1988 encouraged us to transplant early in 1989.
Although both adventitious root score and volume were higher in
plants of lower growth types, it is not clear based on root and shoot
correldtions whether the presence of adventitious roots growing from
red
~lover
crowns is the direct result of a non-flowering or late-
flowering habit or the indirect result of larger crown diameters
associated with non- or late-flowering types.
Indeed, 8mall but
significant correlations between crown diameter and adventitious root
measurements indicate that plants with larger crowns also tend to have
more adventitious roots.
Effect of selection for adventltious root scores
VARIATION IN METRIC CHARACTERS AMONG CROSSES AND CROSSTYPES.
Significant variation among the 32 single-cross progenies was found
for aIl of the dependent quantitative variables.
However, by grouping
the single-cross progenies according to the three types of crosses
(S+, SI and S-) the analysis of variance revealed significant
variation for only one quantitative variable: crown diameter.
S+
progenies (derived from two parents of the high root selection) had
significantly larger crown diameters (Table 5).
Selecting for
adventltious roots thus led to larger crowns in the progeny.
While
adventitious root scores were significantly different among the three
types of single-cross progenies, no significant difference was
(
observed for adventitious root volume, the probability level being
slightly over 0.05 (Table 5).
Difficulties 1n achieving a sufficient
Table 5
Mean adventltious root scores and volumes and Mean crown diameter for
the three types of single-cross progeny based on mid-parent root
score.
Sample
size
Crown
diameter
4
207
2.82 a
8
2.65
a4
4.12
2
177
2.60 ab
1._5
b
1.88
0
191
2.51 b
1.47
b
1.83
Type of cross
(Mid-parent
root score)
--------
Adventltlous
root score
----
Adventlt10us
root volume
.2.
----
e
Values fo11owed by the same letter are not significantly different
at the 0.05 level according to the Duncan's Multiple range test.
• Values fol1owed by the same 1etter are not significantly different
at the 0.15 experimentwise error rate according to a multiple
comparison procedure that follows the Friedman's test •
.2.
Adventitious root volumes were not significantly different at the
0.05 level fo11owtng an analysis of variance.
61
(
level of accuracy in measuring adventitious root volumes would explain
the non-significant effect of cross-type on this variable.
Generally
1arger residual mean squares were obtained by grouping the 32
progenies into three classes, implying that progenies with different
characteristics were grouped under the same crosstype.
VARIATION IN SCORES AHONG CROSSES AND CROSSTYPES.
The 32 slngle-
cross progenies showed significant (p 0.01) variation for the three
types of scores, namely, growth types, adventitious roots and taproot
scores.
When grouped into crosstypes, there vere significant
differences (p 0.05) only for score of adventitious roots (Table 5).
The effect of cross type on progeny adventitious IOOt score vas not
linear, 5- and SI progenies being almost identical in root score and
both significant1y different from S+ progenies.
The average
adventitious root score of the S+ progenies was almost twlce as large
as the S- or SI progenies.
Frequency distributions of the
adventitious root scores for the S- and SI progenies were not
significantly different among them but vere both significantly
different (p 0.05; Kolmogorov-Smirnov test) from the S+ progeny
frequency distribution whlch was skewed toward larger root scores
(Figure 1).
The distribution of adventitious root scores in the the three
types of progenies cannot be explained solely by additive genetic
variance (Figure 1).
SI progenies are not intermediate to S+ and S-
progenies as wou1d be expected with additive genetic variance.
The
expression of adventitious roots may partly be under the control of
recessive allele(s).
(
HERITABILITY OF THE ADVENTITIOUS ROOT TRAIT.
coefficient of 0.30
(Y~1.31
A linear regression
+ 0.30 X; SE-0.029, n-575) vas found
•
Fiaure 1.
Frequency distribution of the adventitious root score of three types
of single-cross progenies evaluated in Fall of 1989. A. Distribution
of progeny where both parents had an adventitious root score of O.
Distribution of progeny where one parent had an adventitious root
score of 0 and one parent had a score of 4.
c.
Distribution of
progeny where both parents had an adventitious root score of 4. Roat
scores: O-no adventitious roots, 4=profuse adventltious roots •
••
B.
63
(
a)
en
LOW ROOT SINQ.E-CROSS PROGENY
80
z 70 ·
~ 60
0
62
~
LIJ
en 50
m
0
40
58
1
41
~ 30
0:::
19
LIJ
m 20 ·
:J
:l
Z
13
10
0
1
o
123
ADVEN11TIOUS ROOT SCORE
1
4
b) INTERMEDIATE SINGLE-CROSS PROGENY
80
zo 70
~ 60
en
ffien
50
~ 40
~ 30
ffiDl
60
42
37
22
20
16
~ 10
z
o
o
1
2
3
ADVEN11TIOUS ROOT SCORE
4
C) HIGH ROOT SINQ.E-CROSS PROGENY
80 ·
en
z 70 ·
~ 60
0
62
56
ffi
en 50
40 ·
~ 30 ·
57
Dl
0
(
15Dl
20
:l
10
:J
z
0
23
9
o
J
1
2
3
ADVENTITIOUS ROOT SCORE
4
64
\
between mid-parent adventltious root score (0, 2 and 4) and the single
cross progeny root score.
This 0.30 regression coefficient represents
the additive portion of the genetie variance for the adventitlous root
score (Falconer 1981).
A narrow-sense heritability estimate of 0.15
was computed from the analysis of variance of the 78 half-sib families
in the parent population (Table 6).
Considering the Iow heritability
values obtained by the two methods of computation, progeny testing
would be needed to ensure successful selection of this root trait.
However, since the adventitious root trait appears to be partially
under recessive gene control, selection response may be somewhat
better in the direction of high adventitious roots than wouid be
expected from the 0.30 heritability estimate.
Conclusions.
The visuai scale for adventitious root rating was found to be as
good or better than the corresponding root volume.
Adventitious root
volumes were difficult to measure, especially when they were small.
Measuring adventitious root weight or volume in a destructive manner
would certainly provide more accuracy but would pose a problem in
malntalning plants for crossing purposes.
An alternative would be to
select plants with larger adventitious roots ln their second growing
season.
Adventitious roots would then be larger and easier to
measure but each cycle of selection would take twice as long.
In the course of digging the FI single-cross progeny it was noted
that a few crosses consistently had no adventitious roots in aIl of
their progeny while no cross consistently had a high adventitious root
score for the 20 plants sampled.
It seemed the genetic control for
the absence of adventitious roots was less environmentally dependent
65
Table 6
Ana1ysis of variance of the adventitious root score of 78 half-slb
familles.
Source of variation
df
E.M.S.
Mean square
2
8.225
77
2.454
2 +
2
2
0w
2.42 0b*r + 3 X 2.42 Ob
Families*Blocks
150
1.978
2 +
2
0w
2.42 0b*r
Sampling error
326
1.631
2
0w
Blacks
Familles
(within families)
Average number of plants per experimental unit: 2.42.
The expected Mean squares (E.M.S.) are glven where
2 is the within
0w
fami1y component, O~*r is the faml1y X block interaction component and
O~ Is the between-family component. The narrow-sense heritability
estimate for adventitious r~"
2
t - O~/(O~ + 0;) = 0.25 h
.,
~core (h 2 ) ls computed from
66
than that controlling their presence.
The herttabil1ty value computed
in this study indicates the possibility of selecting for improved
adventitious root growth in red clover plants.
Although
s~lectlon
for
this root trait did not lead to shifts in growth types (first year
flowering habit), a trend towards larger crowns was associated with
more adventitious root growth.
Larger crowns may provide more sites
for adventitious root initiation.
Therefore adventitious root growth
would be more closely related to crown size than to growth types.
67
REFERENCES
,1
AVENDANO, R.E. and DAVIS R.t. 1966. Lateral root development in
progenies of creeping and noncrt:!eping-rooted Medicago sativa L.
Crop Sei. 6: 198-201
SIRO,
J.~I. 1948. Early and late types of red claver.
28:444-453
Sei. Agr.
BOHM, W. 1979. Methods of Studying Root Systems. Springer-Verlag,
Berlin.
BURDETT, A.N. 1979. A Nondestructive method for measuring the volume
of intact plant parts. Cano J. For. Res. 9: 120-122
BUSCH, R.H. and DAVIS, R.L. 1969. Correlations among root and
aerial characteristics of crosses between creeping-rooted and
noncreeping Medicago sativa L. Crop Sei. 9: 376-377
CARADUS, J.R. 1981. Root morphology of some white clovers from New
Zea1and hill country. N. Z. Jour. Agr. Res. 24:349-351
CARADUS, J.R. 1979. Selection for root hair length in white clover
(Trifolium repens L.). Euphytica 28: 489-494
CARADUS, J. R. 1977. Structural variation of white claver root
systems. N. Z. Jour. Agr. Res. 20:213-219
CHOO, T.M. 1984. Association between growth habit and persistence in
red claver. Euphytica 33:177-185
CRESSMAN, R.M. 1967. InternaI breakdown and persistence of red clover.
Crop Se1. 7:357-361
DANIEL, w.w. 1978.
Applied Nonparametric Statistics.
Houghton Miffl1n CO., Boston.
p. 23},.
FALCONER, D. S. 1981. Introduction to Quantitative Genetics, 2nd ed.,
Longman, New York. 340 p.
FARRIS, N.F. 1934. Root habits of certain crop plants as observed in
the humid soils of New Jersey. Soil Sci. 38:87-111
GIBSON, P.B. and TRAUTNER, J.L. 1965. Growth of white claver with and
without primary roots. Crop Sei. 5: 471-479
HANSEN, J.L. and VIANDS, D.R. 1989. Response from phenotypic recurrent
selection for root regeneration after taproot severing in
aHalfa. Crop Sel. 29:1177-1181
HEINRICHS, D.H. and MORLEY, F.H.W. 1960. lnheritance of resistance ta
winter in jury and its correlation with creeping rootedness in
aHalfa. Cano J. Plant. Sel. 40:487-489
r
08
1
MOKHTARZADEH. A•• LEFFEL. R.C. and BEYBR. E.H. 1967. MaternaI line
selection for perslstence in red clover, Trifolium pratense L.
Crop Sci. 7: 264-266
MONTPETIT, J.M. and COULMAN, B.E. 1991. Relationshlp between spring
vigor and the presence of adventitious roots in established
stands of red clover (Trifolium pratense L.). Cano J. Plant Sei.
(ln press).
McINTOSH, M.S. and MILLER. D.A. 1980. Development of root-branchlng
in three alfalfa cultivars. Crop Sei. 20:807-809
O'TOOLE, J.C. and BLAND, W.L. 1987. Genotyplc variation ln erop plant
root systems. Adv. Agron. 41: 91-145
PEDERSON, G.A., HILL, R.R. and KENDALL, W.A. 1984. Genetie variabil1ty
for root characters in alfalfa populations differing in
wlnterhardlness. Crop Sei. 24:465-468
PERFECT, B., MILLER, R.D. and BURTON, B. 1987. Root morphulogy and
vigor effects on wlnter heaving of establ1shed aHaHa. Agron.
J. 79: 1061-1067
RODRIGUES, G.H.S. and SMITH, S.E. 1989. Evaluation of screcning
procedures for breeding creeping-rooted aHaHa. Crop ScL
29:228-230
SAS INSTlTUTE INC., 1985. SAS Users Guide: Statistics, Version 5
Edition. Chap. 20, pp. 433-506
SAWAI, A., GAU, M. and UEDA, S. 1986. Difference in root system among
growth types of red clover. J. Japan. Grass!. Sei. 32:164-166
SlDDIQUI, W.M., HALISKY, P.M. and LUND, S. 1968. Relatlonshlp of
clipping frequency to root and crown deterloration in red clover.
Phytopath. 58:486-488
SMITH, D. 196.3. Rellabll1ty of flowering as an indicator of wlnter
survival ln red clover. Cano J. Plant Sei. 43:386-389
SMITH, D. 1957. Flowerlng response and winter survival in seedHng
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SMITH, R.R. 1988. Selection for root type in red clover. In G.e.
Marten et al, (eds.) Persistence of Forage Legumes. Proc. of a
trilateralworkshop held in Honolulu, Hawaii, 18-27 July, 1988.
American Society of Agronomy. Madison, WI, USA.
SPEDDING, C.R.W. and DIEKMAHNS, E.C. 1972. Grasses and Legumes ln
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Statistics, 2nd edition. McGraw-Hill CO. p.219.
i
69
STEPPLER, H.A. and RAYMOND, L.C. 1954. Note on the management of red
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TAYLOR, N.L. 1980. Clovers. ln W.L. Fehr dnd M.H. Hadley (eds.),
Hybridization of Crop plants. American Society of Agronomy.
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TAYLOR, N.L., STROUBE, W.H., KENDALL, W.A. and FERGUS, EoN. 1962.
Variation and relation of clonaI persistence and seed production
in red claver. Crop Sei. 2:303-305
TEREKHOVA, A.F. 1956. Study of the root system in red clover. Bot. Zh.
SSSR 41 :553-558
THERRIEN, H.P. and SMITH, D. 1960. The association of flowering habit
wlth winter survival in red and alsike clover during the
seedl1ng year of growth. Cano J. Plant ScL 40: 335-344
THROUGHTON, A. and WHITTINGTON, W.J. 1969. The significance of
genettc variation ln root systems. p.296-3l'1 in W.J. Whittington
(ed.) Root Growth. Proc. of the 15th Easter School in
Agricultural Sei. Un. of Nottingham, 1968. Butterworths, London.
TOWNSEND, C.E. 1964. Correlation among characters and general lack of
persistence in diverse populations of alsike clover, Trifolium
hybridum L. Crop Sei. 4:575-577
V lANDS ,
D. R. 1988. VariabiUty and selection for characters associated
with root regeneratlon capabUity in alfalfa. Crop Scl. 28:232236
WOODFlELD, D.R. and CARADUS, J .R. 1990. Estimates of hcritability
for, and relationshlps between, root and shoot characters of
white clover II. Regression of progeny on mid-parent. Euphytica
46:211-215
'•
!
,
70
CONIŒCTUIG TKXT
Adventitious root growth from the crowns of red clover plants
undoubtedly plays a role in maintaining plants that have logt thelr
taproot.
If the adventitious root type was under genetic control,
this would offer a possibility of developing cultivars wlth improved
persistence.
The association between flowering types (growth types) and
perslstence ln red clover was recognized several decades ago.
Late
flowering or nonflowering types (single-eut) are generally more
peristent than early-flowering types
~
(doubl~-cut).
The work of Sawal
al (1986) showed a relationship between growth types and
adventitious root production, late- or nonflowering types producing
more of this root type.
More work was needed to better understand the association between
flowering habit, adventitlous root growth and persistence.
An
experiment was thus designed to look at the heritability of
adventitious roots and their association with growth types under
spaced plantings.
The impact of flowering habit of individual plants
on winter survival was a1so sssessed.
LITERATURE CITED
SAWAI, A., GAU, M. and VEDA, S. 1986.
Difference in root system among
growth types of red clover. J. Japan. Grassl. Soc. 32:164-166
'':
.&
71
IV. THE DEVELOPMENT
(
or
ADVEHTI'rIOUS 1000S lB SOLID SUDIRGS
RED CLOVEI (TrifoUua pratenae L.)
ona
or
TVO GIOVlHG SEASOIiS.
ItmlODUCTION
01der red clover plants are thought to persist longer due to the
proliferation of adventltious roots from their crown (Taylor et al,
1962; Cressman, 1967).
Plants entering their third or four th year of
growth will often rely entirely on adventitious root growth for
support as the main taproot is often completely disintegrated
(Cressman, 1967).
Cultivar differences for rooting ability are known
to occur in alfalfa and white clover (Smith, 1951; Avendano and Davis,
1966; Caradus, 1977; Farris, 1983) but have not been reported in red
c1over.
A previous study has shown that the presence of adventitious
roots in individual plants of red clover is under genetic control
(Montpetit and Coulman, 1991, unpublished data).
However. this study
was conducted in a breeding population under spaced plant conditions
and gives no indication whether different cultivars have different
capabilities of producing adventitious roots in sol id swards.
Forage
yie1d of genotypes grown in solid seedings are not always correlated
to spaced plantings (Green and Eyles, 1960; Davies and Reusch, 1964).
This could also be the case for root characters.
An objective of this research was to examine the production of
adventitious roots of six red clover cultivars under sward conditions
for a period of two growing seasons and to monitor changes in the
ratio of adventitious root volume to total root volume over the same
period.
MATElUALS AND METHODS
(
Six commercial cultivars of red clover were seeded with a row
drill at the rate of 10 kg ha-Ion May 23, 1988 on a Chicot fine sandy
",
i
72
loam at the E. A. Lods Research Farm. Macdonald College. Sainte-Anne
de Bellevue. Quebec.
four blocks.
The field layout was a split-plot design with
Cultivars were randomly assigned to the m,lin plot \lnits
which were 1.5 X 4.5 m in size.
The three sampling dates were
randomly assigned to the sub-plot units which were 1.5 X 1.5 m in
size.
The three sampling dates were October 27. 1988. May 13 and 14.
1989 and September 9 and 10. 1989.
The six cultivars were the
diploids 'KUHN', 'OTTAWA', 'PROSPER 1', 'PERSIST'. 'ARLINGTON' and the
tetraploid 'SALLY'.
At each of the three sampling dates. plant numbers within two
randomly placed 0.5 m2 quadrats were recorded for each combination of
replicates and cultivars.
of these 24 plots.
Ten plants were then harvested within each
Individual plants were excavated with a spade at
and approximate depth of 20 cm.
a standard length of 12 cm.
adventitious root growth
00
Roots were washed in water and eut to
Plants were glven a score for
a 0 to 4 visual scale (O=no adventitious
root growing from the crowo; 4=numerous adventitlous roots growing
from the crowll).
of the taproot
taproot).
A visual score was also given to describe the size
(O~no
or a very much reduced taproot; 4=prominpnt
Taproot and total root volumes were found by water
displacement by selectively dipping the root parts in a water filled
bucket placed on a top loading electronic scale (Burdett, 1979).
Total root volume was determined by immerslng the entire root system,
while taproot volume was determined when adventitious roots were held
out of the water.
subtraction.
Adventitious root volume waF ca1culated by
Fresh weight of the foliage was found by subtracting
total root volume from total plant weignt.
ln this case, total root
73
weight was assumed to be the same as total root volume.
Previous
observations (Unpublished data) indicated that there was very little
difference between total root volume and weight, at least within the
accuracy of the scale used.
Statlatlcal analyses
Analysis of scores was done by the Friedman's test (Daniel,
1978).
A separate analysis of the effect of cultivars on scores was
done for the three sampling dates.
The effect of dates on scores was
not tested since this analysis would be much dependent on the use of a
constant scale over the three sampling dates.
Visual rating was
constant within each of the three dates but may have changed over the
duration of the experiment.
The quantitative data were submitted ta
an analysis of variance (GLM procedure, SAS, 1985) to test the effect
of cultivars and dates on metric characters (stand density, fresh
weight of foliage, adventitious rort volume, taproot volume, total
root volume and ratio of adventitious root to total root volume).
RESULTS AND DISCUSSION
Stand establishment was slow and non-uniform due to dry weather
conditions after seeding.
Except for the second sampllng, slgniflcact
dlfferences (p(O.OI) in stand establishment were noticeable among the
six cultivars (Table 1).
In general, cultivars that establisbed weIl
maintained a higher number of plants m- 2 throughout the experlment.
In the spring of 1989, the number of plants m- 2
different (p)O.OS) among the six cultivars.
was not significantly
Differences among
cultivars for stand density can either be attributed to differences in
seed quality and number of hard seeds or to cultivar differences in
(
drought tolerance.
Stand densities generally declined over time,
although the spring of 1989 sampling had the lowest mean population.
TABLE 1
Stand densities (plants m- 2 ) at three sampling dates of six
cultivars seeded in May of 1988.
------------------------------------------------------------------CULTIVAR
SAMPLING DATE
--------------------------------------
----------
05/13/1989
----------
PERSIST
32.0 ae
21.0·
26.3 a
26.4 a
KUHN
32.8 a
18.5
21.3 ab
24.2 a
SALLY
29.3 ab
14.8
11.8
c
18.6
b
ARLINGTON
23.3
bc
10.3
17.8
bc
17 .1
bc
PROSPER 1
20.8
c
11.3
13.8
e
15.3
be
OTTAWA
17.5
c
8.0
11.8
e
12.4
c
MEAN
25.9 a
.2
14.0 c
09/09/1989
AVERAGE OF
THREE DATES
10/27/1988
----------
17.1 b
------------
19.0
e MeaDS followed by the same letter are note slgnifieantly
different at the 0.05 level of probability according to the
Duncan's Multiple Range Test.
• Means for the second sampling date were not significantly
different at the 0.05 level of probability follow1ng an analys1e of
variance.
~
Means for sampling dates followed by the same let ter are not
significantly different at the 0.05 level of probability according
to the Duncan'e Multiple Range Test.
7S
(
The increase in plant population from spring of 1989 to fall of 1989
may be the combined result of the late establishment of hard seeds
that did not germinate the previous year and the recovery of plants
that appeared dead in the spring sampling.
Taproot deterioration was
not apparent even during the third sampling.
There were no significant differences among cultivars in taproot
and adventitious root scores at any of the three sampling dates.
However, cultivars were significantly variable (p 0.01) for taproot
volume, adventitious root volume, total root volume and fresh weight
of foliage, but not in the proportion of adventitious roots (p 0.05).
Plant population could not be used as a co-variable in the analysis of
variance, its effect being confounded with that of cultivars.
Thus,
no conclusions on cultivar differences could be drawn.
Multiple correlations betveen shoot and root variables and plant
population.
Stand densities were moderately correlated with the three root
volumes and fresh weight of foliage (Table 2).
With the exception of
low correlations with weight of faliage and score of adventitious
root, plant population was not signlficantly correlated with any of
the other variables at the second and third sampling dates.
The
negative correlation between stand density and shoot and root size was
therefore more conspicuous shortly after stand establishment.
In the
second and third samplings plant populations probably had reached a
level where competition among neighboring plants for space was
neg1igib1e.
In the spring of 1989, stand density correlated only with
adventitious root score.
Although small, this posltive correlation
(r=0.22; p 0.01) indicates a trend toward better spring growth
7tl
Tab1e 2
Multiple correlations for root and shoot variables in a solid
seeding of red clover established in May 1988 and samp1ed in fdll of
1988, spring of 1989 and fall of 1989.
Taproot Adventitious Taproot
score
root vollml:! voluœ
Total
root
vol\.111e
(1) 0.018
(2) 0.œ1
~
adventi tious
roots, (0-4)8
(3) 0.Œ1
~
Score of
Taproot
~~.
Adventitious
~ voll.lœ
(
)
Taproot
voIlee (~)
Total root
voIlee (~)
~
0.465
0.688
0692
0.002
0.134
0.121
**
**
**
0.257
0.090
0.344
~
0.163
0.450
0.560
*
~
0.179
0.210
0.341
*le
~
*le
*
*le
*le
*le
*le
*le
0.356
0.244
0.504
*le
Fresh
Stard
we1ght of density
follage
0.345
0.376
0.525
*le
0.444
0.366
*Ir
**
*le
**
0.156 * 0.212 **
*le
0.463
0.492
*le
0.395
0.453
0.589
*le
0.960
0.944
0.937
*le
*le
*le
**
*Ir
*le
**
0.468 **
0.543 **
0.592 **
0.807
Ô.674
0.695
*Ir
**
**
0.874 **
0.762 *Ir
0.798 **
Fresh wef.ght
of foliage (g)
-{).190
0.218
0.016
-{).255 **
0.121 tfi
-{).106 NS
-{).379 **
-{).109 NS
-{).043 NS
-{).423
-{).462
0.002
-{).169
Scores of adventitious roots: O-no adventitious roots, 4~profuse
adventitious root growth.
.
,,,"
(1) Correlations for the first samp1ing (10/27/1988) •
(2) Correlations for the second samp1ing (05/13/1989).
(3) Correlations for the third samp1ing date (09/09/1989).
**
-{).068 NS
-{).070 tfi
Significant at the 0.05 and 0.01 levels, respectively,
according to the Spearman Rank Correlation procedure. NS, Nonsignificant at the 0.05 level of probability.
, Scores of taproot: Oano predominant taproot, 4=single weIL
developped taroot.
tfi
-{).œ5 tfi
-{).l24 tfi
0.076 NS
., **
e
*le
**
**
**
tfi
77
recovery (thicker stands) in plants with more adventitious roots.
(
This agrees with previous findings (Montpetit and Coulman 1991, in
press).
The largest correlations were found between taproot volume, total
root volume and fresh weight of foliage (Table 2).
The close
relatlonshlp between total root volume and weight of foliage is in
agreement wlth previous root studies (Caradus, 1977, 1981; Avendano
and Davis, 1966).
Taproot volume accounted for 95 %, 92 % and 85 % of
the total root volume at the first, second and third sampling,
respectively.
The high proportion of taproots to total roots observed
throughout this experiment explains the high correlation betwean
taproot volume and total root volume.
Even though adventitious roots
were proportionally smaller (5, 8 and 15 % of total root volumes at
the three samplings) the adventitious root volume had moderate
correlation with total root volume, fresh weight of foliage and
adventltious root score at the three samplings (Table 2).
Adventitious root volume and score were not highly correlated to
taproot volume or score, the largest correlation among these variables
being 0.34 (Table 2).
It seems taproot size has only a minor effect
on the size of adventitious roots.
Some correlations improved over the three sampling
dat~s.
This
is the case of adventitious root and taproot volumes and their
corresponding scores, namely, adventitious root score and taproot
score, respectively (Table 2).
The relationship between adventitlous
root volume and total Toot volume also increased wlth time.
This
would reflect the fact that adventitious roots became proportionally
bigger with time.
78
Effeet stand age on the proportion of adventitlous roots
The three root volumes measured ln this experlment were, on
average, significantly larger for the last sampling date (Table 3).
The ratio of adventitlous root to total root volume also was
significantly larger in the last samplins (Table 3).
This agrees with
Cressman (1967) and Taylor et al (1962) who observed the predominance
of adventitious roots in two to five year old red clover stands.
CONCLUSIONS
Although taproot deterioration was rarely observed in this
experiment, including the last sampling, the data suggest that
adventitious root proliferation begins early in the life of a red
clover plant.
It would appear from our observations that adventitious
roots are not produced in response to taproot deterioration but rather
as a normal part of the red clover root development.
Long term
monitoring of adventitious root volume and its ratio with total root
volume would be needed to confirm the trend toward proportionally
larger adventitious roots as the stand ages.
It was impossible to separate the effect of cultivars on root
variables from that of plant populations.
Correlations between adventitious root volume and both total root
volume and fresh weight of foliage became more pronounced as the stand
aged.
Therefore, the presence of adventitious roots would not only be
associated with improved
persist~nce
(Cressman, 1967) but also with
increased productivity, even before internaI breakdown and taproot
rots start to be significant.
79
Table 3
Effect of time (date of sampling) on the volume of adventitious roots
and on the ratio of adventitious root to total root volume in red
clover stand establ1shed in May ot 1988.
Stand age
Adventitious
Taproot
Total root
adventitious to
root volume
(cm3 )
5 months
12 months
0.62 a
16 months
1.72
b
Ratio of
total root volume
6.77 a
7.31 a
0.05 a
6.04 a
6.66 a
0.08 a
8.39
b
10.10
b
0.15
b
9 Means followed by the same let ter are not significantly different at
the 0.05 level according to the Duncan' s Multiple Range Test.
•
80
unllERCBS
AVENOANO, R.E., and DAVIS R.L. 1966. Lateral root development in
progenies of creeping and noncreeping-rooted Medicago sativa L.
Crop Sei. 6: 198-201
BURDETT, A.~. 1979. A Nondestructive method for measuring the volume
of intact v1ant parts. Cano J. For. Res. 9: 120-122
CARAOUS, J .R. 1990. The structure and function of white c10ver root
systems. Adv. Agron. 43: 1-46
CARADUS, J.R. 1981. Root growth of white clover (Tri.folium repens L.)
l i nes !n glass-f ronted containers. N. Z. Jour. Agr. Res. 24: 4354
CARADUS, J. R. 1977. S tTuctu1'al variation of white c10ver root
systems. N. Z. Jour. Agr. Res. 20:213-219
CRESSMAN) R.!of. 1967. Interna1 breakdown and persistence of red clover.
Crop Sei. 7 :357-361
DANIEL, W.W. 1978. Applied Nonparametric Statistics.
Houghton Miffl1n CO., Boston.
p. 231.
DAVIES, E.W. and REUSCH, J.D.H. 1964. The assessment of herbage legume
varieties. 1. Lucerne. J. Agdc. Sei. 63:61-68
FARIS, M.A. 1983. Progress report on a creeping alfalfa trial at the
Ottawa Research Station. Forage Notes 37:67-70
GREEN, J.O. and EYLES, J.C. 1960. A study in methods of grass var1.ety
testing. J. BrU. Grasslnd. Soc. 11:124-131
SAS INSTITUTE INC., 1985. SAS Users Guide: Stat1stlcs, Version 5
Edi tion. Chap. 20, pp. 433-506
SMITH, D. 1951. Root branching o( alfalfa varieties and strains.
Agron. J. 43:573-575
TAYLOR, N.L., STROUBE, W.H., KENDALL, W.A. and FERGUS, E.N. 1962.
Variation and relation of clonal persistence and seed production
iil red clover. Crop Sei. 2:303-305
(
81
V. GENERAL DISCUSSION AND CONCLUSIONS
Pre-lious attempts to increase the longevity of red clover were
aimed at improving tolerance to root and ct"own rot pathogens or
selecting for late flowering types.
In spi te of taproot
deterioration, some red clover plants were found to be able ta survive
through secondary root growth (Taylor
~
al 1962; Cressman 1967).
This phenomenon was also observed throughout this study.
ln the
sampling of production fields, correlations of 0.46 and 0.65 were
found between spring vigor and advent itious root scores 1 n 3 and 4 yr
old plants for springs of 1988 and 1989.
It was assumed that
individuals with a high spring vigor score wou1d be more persistent
due to their early season competitive advantage.
Planta with a vigor
score of 0 or l were not likely to survive through the growing season
since they were dying or showed ve::y weak growth.
The sampling of three year old research plots (plants entering
their fourth growing season) prC'vided results similar to those
obtained in the sampling of the two production fields.
roots clearly played a
Adventitious
raIe ln the persister.,ce of these three year old
plants since 86 % of the total root volume was made of adventitious
roots.
Considering this high proportion of advent 1 tious roots, the
correlation between spring vigor and adventitious root scores (r=O.60)
was less than antic1pated.
Weak plants may have been dead by the time
of sampling sinee the sampling of research plots was done
approximately three weeks after the sampling of production fields.
Maximum differentlation of spring vigor may thus be obté'ined by
sampling in early May under our climate.
l t should be noted that the
correlation between fresh welght of foliage and adventitlous root
82
volume (the quanti tat i ve equi valents of the above-mentioned scores)
was sUghtly h!gher (r=O. 70).
Sm! th, (1988) described red clover root types according to a
visual sea1e from 1 to 5, the larger values being assigued to plants
with increasingly more profuse adventitious roats while the lower
values was given ta plants that were predominantly taprooted.
According to his scale. taproots and adventitious roots were a8sumed
to be negatively correlated.
In the May 1988 sampling of the present
study, adventitious roots and taproots were scored on two different
scales.
No correlation was found between taproot score and
adventitious root score.
In the sequentia1 sampl1ng of solid
seedings, adventitious root growth appeared to be independent of
taproot growth.
Indeed, profuse adventitious root growth cou1d be
found on plants with healthy taproots.
One objective of the sampling of research plots in 1988 was ta
compare viaual s"ores with quantitative measurements of the same root
traits.
Both adventitious root and taproot scores correlated weIl
with their quantitative counterparts, nl:lmely, adventitious root volume
and taproot volume, respectlvely.
(selection experiment,
However, in subsequent sampl1ngs
1988 and 1989) on1y correlations between
adventitious root score and volume had moderate to high coefficients,
taproot score and volume often showing very litt1e relationship.
The non-des tructi ve measurement of root volumes udng Archimede' s
principle was found ta work well with large root '·olumes such as
taproot volume.
However, the level of accuracy in measuring
adventi tious root volume was reduced in fall of 1989 due ta the small
size of these roots.
Adventitious root volumes were a1so diff!cult to
83
measure in 1988.
Pederson
~
al, (1980) also reported large error
variances in studying root traits cf red clover.
Therefore, selection
was done on adventitious root score rdther thdll on
dJvl~ntltious
root
volume, the visual scale being considered more descr i pt ive of this
root type.
One cycle of bi-directional selection for e.dventitious root score
indicated the possibility for improving this root type in red clover.
This is in agreement with the work of Smith (1988).
As opposed to
Smith who selected for roots under solid seedings, st: lect! on and
progeny 'valuation was done under spaced plantings in the present
study.
Since plants were larger than as in solid seE ding, it was felt
that selection was helped by increased root type differentlation.
Spaced plantings were also requi red ta meaSllre flowe ring types and ta
correlate them with root traits measured on the same plants at a later
date.
By comparison, roots of one season old plants grown under
spaced plantings were nearly seven times ag large as roots from plants
grown in solid seedings.
Smith (1988) found a greater selection response towards the
absence of fibrous roots.
In this study, parents were Dot included in
the progeny evaluation since they would have had to be prol,agated by
cuttings, making lt difficult ta compare root types with their progeny
whlch were grown from seedl1ngs.
Therefore, it is difficult ta
determine if the response was of the same magni tude in both directions
of selection.
However, the analysis of the frequency distribution of
root scores in the progeny (Figure 1, Chapter IV) suggested that
adventitious roots may partly be under the control of recessive
'.'
al1ele(s).
If thls was the case, selection response should be higher
in the direction of profuse adventitious roots.
84
The type of cross (5+, SI or S-) produced significantly different
progenies for adventitious root score but not for adventitious root
volume.
The high level of variation in measuring adventitious root
volume and the fact that selection was done on root scores would
explain the lack of significant differences for this root volume.
Selection for more adventitious roots also led t0 larger crowns in the
progeny.
Larger
initiation.
crown~
may offer more sites for secondary r00t
Crown size could be the Iink between adventitious root
growth and flowering types in red clover.
Larger crowns were found to
produce more secondary roots in alfalfa (Saindon, lQ85).
The negative
correlation between growth types and adventitious roots would be the
result of larger crowns found in non-flowerlng types.
This negative
correlation between root type and flowering seems to occur in
different germplasm (Sawai
~
al, 1986).
The better winter-hardiness
of non-flowering types may be due to their ability to produce more
adventitious roots.
In spite of the negative correlation found
between growth type and adventitious root score in 1988, progenies of
the S+ single-crosses did not have a significantly lower growth type
score than progenies of the other two types of cross.
Therefore, it
appears possible to select for adventitious roots without shifts in
flowering habit.
In the third part of
t~is
project changes in root types and
proportions were evaluated over time.
Differences in cultivar
establishment did not allow the study of their rooting ability.
The
proportion of adventitious roots steadily increased over the three
(
sempling dates.
While taproot volume a1so increased over the two
growing seasons, the rate of adventitious root growth was even faster.
,
85
This
sugg~sts
that adventitious roots are not initiated in response to
taproot deterioration but are rather induced as a normal part of the
red clover root development.
In fact, taproot Jeterlùfdtlon
hardly noticeable at any of the three sampling datps.
WJg
Genotypes with
a better ability ta produce adventitious roots would persist for a
longer period.
This may give the impression that adventitious roots
are produced in response to taproot deterioration.
Taylor
~
al
(1962) found that sorne clones had more adventitious root growth early
in their development.
Two general conclusions can be Jrawn from this work: 1)
adventitious roots are associated with better persistence in red
clover, 2) adventitious roots appear to be under genetic control.
This implies that more persistent red clover populations could be
developed through selection for more adventitious roots.
However, no
information was obtained on the productivity of red claver plants
surviving solely through adventitious roots.
These plants may be more
drought susceptible due to their shallower root system.
Despite the
positive correlation observed between adventitious root volume and
fresh weight of foliage in older red clover plants, it is conceivable
that their yield was lower than that of younger plants with healthy
taproots.
It may be more profitable to establish new stands of a less
persist2nt strain than keeping stands of a more persistent but lower
yielding strain.
This question needs ta be answered before major
efforts are spent on the development of red clover cultivars with
improved secondary root growth.
86
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{
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"
96
APPEHDII A.
<,
DETAILED ANALYSES OP VAR.IANCE POR. THE PlUT IWfUSCRIPT.
:
97
Table 1
A.O.V. for fresh weight of foliage (g), May 1988: effect of rep1icates
and taproot score.
---------------------------------------------------------------------Source
df
Replicates
2
87.86
0.8062
Taproot score
4
2458.98
0.0143
Replicates * Taproot score
(experimental error)
8
396.95
171
300.13
Sampling error
MS
Pr
F
R-square 0.21
C.V.
68.88
Table 2
A.O.V. for fresh weight of foliage (g), May 1988: effect of replicates
and adventitious root score.
MS
Pr
Source
df
Replicates
2
87.42
0.6514
Taproot score
4
7072.19
0.0001
Replicates * Taproot score
(experimental error)
8
109.26
171
203.44
Sampling error
R-square 0.47
C.V.
56.71
F
98
Table 3
A.O.V. for ratio of adventitious root to taotal root volume, May,
1988: effect of replicates and taproot score.
---------------------------------------------------------------------MS
Pr
Source
df
Replicates
2
0.0042
0.9368
Taproot score
4
1.1496
0.0005
Replicates * Taproot score
(experimental error)
8
0.0643
171
0.0130
F
----------------------------------------------------------------------
Sampling error
R-square
c.v.
0.70
13.32
Table 4
A.O.V. for ratio of adventitious root to total root volume, May 1988:
effect of replicates and adventitious ~oot score.
Source
df
MS
Replicates
2
0.0267
0.4027
Taproot score
4
0.5164
0.0003
Replicates * Taproot score
(experimental error)
8
0.0262
171
0.0244
Sampling error
R-square
c.v •
.
0.43
18.24
Pr
F
99
..
APPENDU B. ILLUSTRATIONS OF ROOT AND GIlOVl'll TYPE RATINGS J DBTAlLED
ANALYSES OP VAillARCE AND DATA HOT PRESENTED IN THE SECOND MARUSCRIPT.
100
Figure 1.
Variation in adventitious root score for the one-season old singlecross progeny grown under spaced plantings and examined in the fail of
1989. A. Root
score~O;
no adventitious root growth from the crown. B.
Root score=1; sparse adventitious root growth from the crown and Iower
stems.
c.
Root
score~2;
crown and lower stems.
several adventitious roots growing from the
D. Root=3j Numerous adventitious roots growing
from the crown and lower stems.
B. Root score=4j Profuse adventltious
root growth from the crown and lower stems.
F.
Comparing extremes ln
root score; root score=4 (left), root score=O (right).
l
l
•
....
102
Figure 2.
Growth types of individua1 red c10ver plants transp1anted in the field
on June 9, 1988 and eva!uated on August 5, 1988. A. Growth typeaO;
rosette on1y.
B. Growth type 1; one ta severa! e!ongated stems.
3
Growth type a 2; a few stems flowering.
flowering stems.
D. Growth type=3; many
E. Growth type-4; a11 stems elongated and f10wering
and !itt1e vegetative growth in the center.
at the time of growth type evaluation.
{
C.
F. Spaccd-p1ant nursery
-- ....
1
.
. '~
"~t
. ,: ",1
'"
d'~
,"
,
fI
104
Table 1
Characteristics of the 44 parents used in the 32 single-crosses made
in the winter of 1988-89.
High adventltious root selection
Parent
59-11
58-1
54-6
52-3
49-3
48-7
45-5
44-12
43-12
39-18
35-10
32-20
29-2
26-9
25-3
14-10
12-6
11-8
6-15
b-9
5-14
5-6
4-6
HFG 9
10-13-4
3-6-0
5-19-2
7-15-2
8-2-2
7-14-0
4-4-4
3-16-0
7-11-0
9-18-4
18-18-2
17-10-2
4-4-4
8-5-0
16-4-2
2-8-2
19-6-0
4-11-2
8-12-4
10-12-2
5-9-0
3-16-0
16-10-2
Low adventitious root selection
SCR
TRV
FWF
Parent
1/72
78
100
83
75
61
60
96
46
128
33
48
56
36
98
68
31
47
35
60
60
23
73
80
622
678
597
720
472
342
385
60-5
59-1
56-16
55-20
48-18
42-14
41-14
38-5
37-11
35-15
31-9
28-13
28-8
26-11
24-11
17-2
11-7
7-12
5-19
4-19
3-l3
nia
0/97
nia
0/100
2/80
0/70
0/81
nia
0/70
nia
0/63
0/97
0/49
0/59
0/81
0/82
0/88
0/59
0/60
0/58
nia
nia
292
946
322
402
384
214
792
413
245
290
243
560
290
269
HFG
nia
nia
15-3-2
4-17-0
19-11-4
17-1-4
12-18-2
4-8-4
10-18-0
7-7-2
4-5-2
13-6-2
16-10-2
19-8-2
9-19-0
2-3-2
4-11-2
9-3-0
11-16-4
5-21-0
6-15-4
SCR
TRV
FWF
nia
nia
nia
48
35
55
65
20
88
45
37
75
55
55
64
65
67
67
14
20
32
45
32
20
643
234
383
708
375
836
487
513
575
494
437
656
285
370
583
126
0/78
0/76
nia
nia
nia
0/90
nia
0/45
nia
nia
nia
0/67
2/115
0/95
nia
0/81
nia
0/87
337
362
215
293
130
409
337
-_.. _------------------------------------------------------------------9
HFG = Half-5ib progeny group; parents were the progenies of seven
polycrosses made to study the inheritance of growth types. SCR = Rate
of self-compatibilitYj numerator = number of seed set, denominator =
number of self-pollinated florets. TRV = Total root volume (cm3 ).
FWF ... Fresh weight of foUage (g).
"
\
105
1
Table 2
Characteristics of the 32 single-cross progenies estab1ished under
spaced p1antlngs in May of 1989 and eva1uated in Septenber of 1989.
Parent age
Number of
observations
Average 9
progeny
adventitlous
root score
Average
progeny
adventltious
root volume
Average
progeny
growth type
(g)
59-11S+ X 5-6S+~
39-18S+ X 26-98+
49-3S+ X 17-2844-12S+ X 11-7S14-10S+ X 12-68+
49-3S+ X 48-7S+
58-1S+ X 52-3S+
29-25+ X 5-145+
56-168- X 28-13854-68+ X 6-9S+
45-5S+ X 14-108+
43-128+ X 4-65+
25-35+ X 11-8S+
38-5S- X 28-8537-118- X 3-13844-128+ X 5-14S+
48-18S- X 3-13S59-1S- X 26-11S32-208+ X 31-9841-14S- X 29-2S+
60-55- X 35-15S41-148- X 11-7S35-105+ X 31-9528-8S- X 4-6S+
6-15S+ X 4-19548-18S- X 17-2858-15+ X 5-19552-3S+ X 37-11545-5S+ X 24-11S42-148- X 7-12S55-208- X 31-9824-11S- X 5-195-
19
20
19
16
18
20
19
15
18
20
20
19
20
20
20
17
19
15
14
19
13
19
19
15
15
20
20
20
20
12
15
20
3.37
3.30
2.84
2.75
2.72
2.70
2.68
2.67
2.67
2.65
2.55
2.37
2.20
2.00
1.95
1.88
1. 74
1. 73
1.71
1.68
1.54
1.53
1.37
1.33
1.27
1.25
1.05
0.90
0.80
0.75
0.67
0.10
6.63
5.45
4.05
8.25
3.39
4.30
5.00
2.93
7.50
4.35
2.20
2.89
3.25
3.15
2.70
4.71
0.63
0.87
1. 57
2.00
2.25
3.00
2.38
2.28
2.15
1.84
3.33
1.32
1.31
2.74
1.62
1.16
1.47
1.21
2.05
0.87
0.73
2.90
0.87
1.80
0.70
0.25
0.25
0.15
0.75
0.73
0.00
1.22
1.85
2.70
1.26
2.20
2.50
2.20
2.29
3.00
2.27
1.71
2.45
1.65
1.40
1.58
1.47
2.15
e
Root score: 0=00 adventitious root growth from the crownj 4a profuse
adventitious root growth from the crown.
~ 8+ for high root parent (root score ~ 4),
(root score
= 0).
s-
for 1o~ root parent
106
(
Table 3
A.O.V. for volume of adventitlous roots (cm3 ): effect of the 32 sIngle
cross progenles, fall of 1989.
---------------------------------------------------------------------Pr F
MS
df
Source
----_._--------------------------------------------------------------3
178.57
0.0106
Progenles
31
100.63
0.0017
Replicates * Progenles
(experimental error)
93
45.15
447
20.01
Repl1cates
Sampling error
R-square
C.V.
0.46
251.86
Table 4
A.O.V. for taproot volume (cm3 ): effect of the 32 single cross
progenles, fall of 1989.
Source
df
Replicates
3
2254.39
0.0022
Progenles
31
3978.53
0.0001
Repllcates * Progenles
(experlmental error)
93
431.89
447
311.86
Sampling error
R-square
c.v.
0.55
44.66
MS
Pr
F
----------------------------------------------------------------------
107
."
r
Table 5
A.O.V. for total root volume (cm3 ): effect of the 32 single cross
progenies, fall 1989.
Pr
F
Source
df
Replicates
3
3090.23
0.0011
Progentes
31
4116.10
0.0001
Replicates * Progenies
(experimenta1 error)
93
529.00
447
343.20
Sampl1ng error
R-square
c.v.
MS
0.55
46.75
Table 6
A.O.V. for fresh weight of foliage (g): effect of the 32 single-cross
progentes, fall of 1989.
Source
df
Replicates
3
507 670.50
0.0001
Progenies
31
115 914.61
0.0001
Replicates * Progenies
(experimental error)
93
26 586.35
447
17 118.44
Sampllng error
R-square
c.v.
0.50
42.00
MS
Pr
F
108
(
Table 7
A.O.V. for crown diameter (cm): effect of the 32 single cross
progenies, fall of 1989.
Source
df
MS
Repl1cates
3
0.488
0.2078
Progenies
31
2.665
0.0001
Replicates * Progenles
(experimental error)
93
0.316
447
0.227
Sampl1ng error
Pr
F
R-square 0.53
C.V.
21.20
Table 8
A.O.V. for volume of adventitious rO(lts (cm3 ): effect of the three
cross types, fa11 of 1989.
Source
df
MS
RepUcates
3
206.74
0.1268
Cross types
2
352.48
0.0554
6
72.37
563
26.22
*
RepUcates
Cross types
(experlmental error)
Sampl1ng error
R-square 0.11
C.V.
318.88
(
Pr
F
Table 9
A.O.V. for taproot volume (cru3 ): effect of the three cross types, fall
of 1989.
Source
df
MS
Replicates
3
2396.12
0.0772
Cross types
2
1708.78
0.1451
6
630.80
563
527.76
*
Replicates
Cross types
(experimenta1 error)
Sampling error
Pr
F
R-square 0.05
C. v.
53.97
Table 10
A.O.V. for total root volume (cm3 ): effect of the three cross types,
faH of 1989.
df
MS
Replicates
3
3431.85
0.0729
Cross types
2
3426.48
0.0818
6
876.18
563
567.80
*
Replicates
Cross types
(experimental error)
Sampling error
R-square 0.07
C. V.
60.16
< "
Pr
Source
F
110
Table 11
A. o. V. for fresh weight of foIiage (g): effect of the three cross
types, faII of 1989.
MS
Pr
F
Source
df
Repl1cates
3
508 854.15
0.0114
Cross types
2
130 459 19
0.1737
6
54 883.88
563
23 489.27
*
Repl1cates
Cross types
(experimental error)
Sampllng error
R-square 0.13
C.v.
60.34
Table 12
A.O.V. for crown dlameter (cm): effect of the three cross types, fal1
of 1989.
MS
Pr
F
Source
df
Replicates
3
0.518
0.6878
Cross types
2
5.188
0.0500
Replicates * Cross types
(experimental error)
6
1.010
563
0.351
Sampling error
R-square 0.08
C.v.
22.36
,
1
111
APPENDU C.
DETAILED ANALYSES OF VARIANCE FOR THE TRIRO HANUSCRIPT.
112
Table l
A.O.V. for stand density (plants m- 2 ) at the first sampling date
(10/27/1988): Effect of replicates and cultivars.
---------------------------------------------------------------------Pr
F
Source
df
MS
Repl1cates
3
28.72
0.2688
Cultivars
5
159.57
0.0007
15
19.86
----------------------------------------------------------------------
Replicates * Cultivars
(experimental error)
R-squal.e
c.v.
0.75
17.19
Table 2
A.O.V. for stand density (plants m-2 ) at the second sampllng date (0509-1989): Effect of replicates and cultivars.
Pr
F
Source
df
MS
Repl1cates
3
41.49
0.3791
Cultivars
5
101.94
0.0616
15
37.65
Replicates * Cultivars
(experimental error)
R-square 0.53
C.V.
43.96
113
Table 3
A.O.V. for stand density (plants m- 2) at the third sampling date
(09/09/1989): Effect of replicates and cultivars.
MS
Pr
F
Source
df
Replicates
3
69.94
0.0317
Cultivars
5
135.87
0.0011
15
18.18
Replicates * Cultivars
(experimental error)
R-square
C. V.
0.77
24.96
Table 4
A.O.V. for stand density (plants m- 2 ): Effect of repl1cates, cultivars
and dates.
df
Source
MS
Pr
F
Replicates
3
111.09
0.0571
Cultivars
5
343.08
0.0003
15
35.49
Replieates
(error a)
* Cultivars
Dates in Cultivars/replicate
combination
2
923.18
0.0001
10
27.15
0.2128
Dates * Replicates (Cultivars) 36
(error b)
19.17
Dates
Dates
R-square
C.V.
*
Cultivars
0.87
23.06
----------------------------------------------------------------------
114
(
Table 5
A.O.V. for volume of adventitious roots (cm3 ): effect of replicates,
cultivars and dates.
df
Source
MS
Pr
F
RepUcates
3
3.004
0.2151
Cultivars
5
10.238
0.0038
15
1.794
2
103.382
0.0001
10
3.984
0.6906
(Cultivars) 36
5.451
648
3.134
Rep1icates
(error a)
* Cultivars
Dates in Cultivars/replicate
combination
Dates
Datp.s
* Cultivars
* Replicates
Dates
(error b)
Residua!
R-square
C. V.
0.21
184.73
----------------------------------------------------------------------
(
115
Table 6
A.O.V. for volume of taproot (cm3 ): effect of replicates, cultivars
and dates.
---------------------------------------------------------------------Source
df
MS
Pr
---------------------------------------------------------------------Repl1cates
3
19.52
0.6564
Cultivars
5
285.31
0.0007
15
35.54
Replicates
(error a)
* Cultivars
Dates in Cultivars/replicate
combination
2
347.47
0.0010
10
54.80
0.2541
Replicates (Cultivars) 36
Dates
(error b)
41.32
Dates
Dates
*
*
Cultivars
Residual
R-square 0.27
C.v.
62.99
648
19.81
116
Table 7
A.O.V. for total root volume (cm 3 ): effect of replicates, cultivars
and dates.
Source
df
MS
Pr
F
Repl1cates
3
36.19
0.4752
Culti vars
5
378.65
0.0004
15
41.28
2
803.48
0.0001
10
68.49
0.3679
(Cult! vars) 36
60.61
648
25.87
Replicates
(error a)
* Cultivars
Dates in Cul ti vars/replicate
combination
Dates
Dates
* Cultivars
* Repl1cates
Dates
(error b)
Residual
R-square 0.30
c. V.
63.39
----------------------------------------------------------------------
117
Table 8
A.O.V. far ratio of adventitious root volume (cm 3 ) ta total root
volume (cm3 ): effect of replicates, cult! vars and dates.
Source
df
MS
Pr
F
Replicates
3
0.0661
0.1752
Cultivars
5
0.0437
0.3357
15
0.0350
2
0.6220
0.0001
.0
0.0249
0.6930
Dates" Replicates (Cultivars) 36
(error b)
0.0342
648
0.0250
Replicates .. Cultivars
(error a)
Dates in Cultivars/replicate
combination
Dates
Dates
* Cultivars
Residual
R-square O. 18
C.V.
169.37