Plant Breeding 111,204-216 (1993)
© 1993 Paul Parey Scientific Publishers, Berlin and Hamburg
ISSN 0179-9541
Pleiotropic Effects of Genes for Reduced Height (Rht)
and Day-Length Insensitivity (Ppd) on Yield
and its Components for Wheat Grown in Middle Europe
A. BORNER 1, A.
J. WORLAND z, J. PLASCHKEl, ERIKA SCHUMANN3 and
C. N. LA~
1 Institut fur
Hir Pflanzengenetik und Kulturpflanzenforschung, Corrensstrasse 3, D-06466 Gatersleben, Ger7Uj, Great
many; 2 Cambridge Laboratory, Centre for Plant Science Research, Colney Lane, Norwich NR4 7UI,
Britain; 3 Institut fur pflanzenzuchtung und Saatgutwirtschaft, Martin-Luther-University Halle-Wittenberg,
D-06188 Hohenthurm, Germany.
With 4 figures and 4 tables
Received June 30, 1992 I Accepted August 5, 1993
Communicated by W. E. Weber
Abstract
Under field conditions in Germany over three growing seasons the pleiotropic effects on yield and its
components of four sets of near isogenic lines carrying the GA insensitive dwarfing alleles Rht1, Rht2,
RhtJ, Rht1+2, Rht2+3 or rht (tall) in four different
genetical backgrounds were examined together with
24 single chromosome recombinant lines segregating
for the GA sensitive dwarfing gene Rht8 and the
gene for day-length insensitivity Ppd1 in a 'CappelleDesprez' background. For the GA insensitive semidwarfs it was shown that in all three years a higher
number of grains per ear was accompanied by a
lower grain weight. Depending on the climatic conditions in a particular year, the increase in grain
number was sufficient to compensate for the reduction in grain size and resulted in higher yields. For
the Ppd1 allele yield advantages were found for
wheats grown under environmental conditions of
middle Europe.
Key words: Triticum aestivum - semi-dwarfnessreduced height - gibberellic acid insensitivity photoperiodic response.
Throughout the wheat producing areas of the
world yields have increased dramatically during the past century. In the presence of suitable
dwarfing genes much of the increase in yield
can be directly attributed to reductions in plant
U.S.
U.S. Copyright Clearance Center Code Statement:
height, where shorter plants are both better
adapted to withstand lodging and its consequential yield losses, and also exhibit a more
efficient distribution of biomass between grain
and straw yield.
The genetic control of plant height is, however, known to be complex involving many
genes, the majority of which, show a positive
correlation between reduced height and reduced yield (LAwet al. 1978). Probably as a
consequence of this complex correlation few
dwarfing genes have been successfully utilized
in breeding programmes. The only commercially acceptable dwarfing genes are the GA
insensitive dwarfing genes (GALE and YOUSSEFIAN 1985, WORLAND and PETROVIC 1988,
BORNER and METIIN 1989) deriving principally
from 'Norin 10' or 'Saitama 27' and the GA
responsive dwarfing genes derived from
'Akakomugi' (WORLAND and LAW 1986).
Various genetic stocks have been developed
to enable the direct and indirect measurement
of the pleiotropic effects of dwarfing genes to
be determined for a range of agronomic
characters. The most precise stocks available
for studying the GA insensitive dwarfing genes
are isogenic lines where a range of different
GA insensitive alleles have been backcrossed
into a number of different varietal backgrounds (GALE and YOUSSEFIAN 1984). As de-
0179-9541/93/1103-0204$02.50/0
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
velopment of isogenic lines by backcrossing
requires the ability to recognize the gene being
introduced in segregating populations, and as
no markers are currently available to tag the
'Akakomugi' genes, these genes cannot be
studied utilizing conventionally backcrossed
isogenic lines. An alternative is to develop
single chromosome substitution lines (LAW and
WORLAND 1973) and then single chromosome
recombinant lines (LAW 1966, 1967). Such
stocks can be classified for the allelic variants
of the genes segregating on the recombinant
chromosome, thus enabling the selection of
lines with known assemblages of genes in a
common genetic background. Then pairs of
'near' isogenic lines can be selected for study
under field conditions.
Despite the near universal acceptance of
semi-dwarf wheat varieties under modem high
intensity agronomic systems, there seems a
reductance to accept such varieties in areas of
Europe such as Germany. In the present paper
the performance under field conditions over
three growing seasons of precise genetic stocks
carrying a range of different dwarfing genes
and a gene for day-length insensitivity are examined.
205
plot and used to calculate the number of grains per
ear, the 1000-grain weight and the yield of single
ears. The V-test of MANN and WHITNEY (1947) was
used to determine the significant differences between
the tall controls and their isogenic lines.
For a period from around 15 days before and 15
days after ear emergence the daily mean temperatures were recorded. This period covers growing
stages of Rht wheats where they were most susceptible to climatic stress (LAW and WORLAND 1985).
Single chromosome recombinant lines (Experiment 2): Altogether 24 single chromosome recombinant lines, derived from the cross between the
wheat variety 'Cappelle Desprez' and a substitution
line in which chromosome 2D of 'Cappelle Desprez'
had been replaced by its homologue from the Italian
semi-dwarf variety 'Mara' (WORLAND and LAW
1986) were used. Lines were selected at random from
a larger group of pre-classified recombinant lines, in
order to provide six lines for each of the four genotype classes available for the two genes Ppdl and
Rht8.
Experiment 2 was conducted in the same way as
experiment 1. Each plot was measured for days to
ear emergence, plant height, tiller number (1 m), and
plot yield. Four primary ears per plot were removed
just before harvest and analyzed for their spikelet
number, number of grains, 1000-grain weight and
ear yield.
Materials and Methods
Results
Near isogenic lines (Experiment 1): Four sets of
near isogenic lines carrying the alleles Rhtl, Rht2,
RhtJ, Rht1+2, Rht2+3 or rht (tall) in the genetical
backgrounds of the wheat varieties 'April Bearded'
(A), 'Bersee' (B), 'Maris Huntsman' (H) and 'Maris
Widgeon' (W) - kindly supplied by Dr. M. D.
Gale, 'Cambridge Laboratory', Norwich - were
grown in a randomized design with six blocks of
4.5 m2 plots cultivated over three years
(1989-1991). The first twO experiments were grown
at Bemburg and the last one at HallelHohenthurm,
both in the middle of Germany. In the first season
(harvest 1989) the sowing was delayed until]anuary
because of problems in the transit of basic seed
stocks to Germany. In the following two years the
sowing time was within the first ten days of October, which is the optimal sowing date for the area.
In order to eliminate confounding factors the plants
were treated prophylactically with fungicides and
were prevented from lodging with wide mesh nets.
No growth regulators were applied.
Besides plant height, the date of ear emergence,
the number of main tillers (scored on a row length of
1 m in each plot) and the combine-harvested plot
yield were measured. Main shoot data were obtained
from a random sample of 20 leading tillers in each
Experiment 1
The effects of different Rht alleles on reduction
of height are given in Figure 1. Over all genetical backgrounds and years the same ranking
was observed: Tht < Rhtl < Rht2 <
Rhtl+Rht2 < RhtJ < Rht2+RhtJ. Absolute
values did however vary between varieties and
years.
For the pleiotropic effects on grain yield and
yield components it could be shown, that the
most consistent effects of the Rht genes were
on the number of grains per ear and on grain
weight. The isogenic lines usually produced
significantly more grains than their Tht controls (Fig. 2). The 1000-grain weights were
however reduced in most of the semi-dwarf
lines, compared to the tall lines over the three
years (Fig. 3).
The mean data of the effects on the other
traits examined, including yield are given in
Tables 1 to 3 (for 1989, 1990, 1991, respectively). Because of winter damage to the whole
'April Bearded' set grown in 1991 the data for
206
BORNER, WORLAND, PLASCHKE, SCHUMANN and
140 r-cm
-=--P-=LA=--=-N-=--T-=---=--H-=-=E=I'---="G=H'--=-T--'---
L.~1I'
-----,
1989
120
100
80
60
40
20
o
April Bearded
Bersee
M. Huntsman
M. Widgeon
cm
140 r - - - - - - - - - - - - - - - - - - - - - - - - - - ,
120 1 - - - . - - - - - - 100
80
60
40
20
o
April Bearded
Bersee
M. Huntsman
M. Widgeon
cm
120 r - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
100
60
40
20
April Bearded
Bersee
M. Huntsman
M. Widgeon
Fig. 1. Height reducing effects of Rht alleles in near isogenic lines of 'April Bearded', 'Bersee', 'Maris
Huntsman' and 'Maris Widgeon' grown in Germany. The asterisks indicate significant differences between
the original variety and their Rht lines (V-test)
tiller number and plot yield were excluded for
this variety and year (Table 3).
Although the mean dates of ear emergence
varied between May 22 in 1990 and June 21 in
1991 (Fig. 4) they seemed to be unaffected by
the dwarfing genes. There were always some
lines that were significantly earlier, and some
lines which were later than the tall control, by
a maximum difference of two days.
For the number of fertile tillers there was a
trend for reduction, compared to the tall control, in 1990 and 1991, especially in the more
extreme dwarf lines. In 1989 where sowing was
very late Qanuary) the overall tiller numbers
were reduced by about 50 %. A significant
increase in tiller number was, however, observed in the lines of 'April Bearded' isogenic
for RhtJ, Rht1+2 and Rht2+3 (Table 1).
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
Yield, determined both as the yield of 20
single ears and as the plot yield was influenced
by the Rht genes in the three years analyzed.
With the exception of the' April Bearded' set,
the extreme dwarfs containing Rhtl + 2, RhtJ
OJ Rht2+3 tended to produce significantly
lower yields. The yields of the Rhtl and Rht2
lines, compared to the controls were higher in
1989 and 1990, but lower in 1991. The late
207
flowering time in 1991 meant that temperatures during the period of grain fill were higher, resulting in a shortened period of grain fill
and yield loss. In the tall background of 'April
Bearded', for 1989 and 1990 where data was
available all the isogenic Rht lines outyielded
the tall controls which were prevented from
lodging.
The harvest index was in the first twO years
GRAIN NUMBER
80 , - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
601---••
40
20
0
, April Bearded
Bersee
M. Huntsman
M. Widgeon
April Bearded
Bersee
M. Huntsman
M. Widgeon
April Bearded
Bersee
M. Huntsman
M. Widgeon
60
50
40
30
20
10
0
70
60
50
40
30
20
10
0
Fig. 2. Pleiotropic effectS of Rbt alleles in near isogenic lines of 'April Bearded', 'Bersee', 'Maris HuntSman'
and 'Maris Widgeon' grown in Germany on the number of grains per ear. The asterisks indicate significant
differences between the original variety and their Rbt Jines (V-test)
208
BbRNER, WORLAND, PLASCHKE, SCHUMANN and
usually significantly higher for dwarf than tall
controls, in 1991, however, only in three cases
was the increase significant.
Experiment 2
The results of the experiment with the single
chromosome recombinant lines are summarized in Table 4.
--=GRAIN
50 ,=g
LAW
Mean values of agronomic characters
In comparing the mean values (Table 4) for the
three seasons it should be remembered that the
delayed availability of seed for the experiment
harvested in 1989 meant that sowing was delayed until January. This late sowing resulted
in greatly reduced tillering, shorr plants and
low plot yields. Most other agronomic charac-
""---__->WEIGHT
--L-
----,
1989
40
20
10
o
April Bearded
60
Bersee
M. Huntsman
M. Widgeon
;:.g--------------------------,
50
30
20
10
o
April Bearded
Bersee
M. Huntsman
M. Widgeon
g
50,------------------------
1991
401--.--
.....
30
20
10
April Bearded
Bersee
M. Huntsman
M. Widgeon
Fig. 3. Pleiotropic effects of Rht alleles in near isogenic lines of 'April Bearded', 'Bersee', 'Maris Huntsman'
and 'Maris Widgeon' grown in Germany on grain weight. The asterisks indicate significant difference
between the origina.1 variety and their Rht Jines (V-test)
209
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
ters were not affected by the delayed sowing
with spikelet number, spikelet fertility, grains
per ear, 1000-grain weight, spikelet yield and
ear yield being at least as good as the average
values of the two subsequent seasons.
The 1991 experiment was subjected to a
relatively harsh winter which resulted in ear
emergence time being delayed by about three
,weeks compared to the two previous seasons.
The later flowering meant plants had to develop and fill their grains under more advanced
summer conditions resulting in significantly
reduced lOOO-grain weights in this season.
Effects of Ppdl
The primary effect of Ppdl is to permit earlier
flowering through early development of floral
primordia, following the satisfying of vernalization requirements, without the need for a
period of long-day treatment. In each of the
three seasons of trials, Ppdl significantly accel-
Table 1. Effects of Rht alleles on yield components in near isogenic lines of 'April Bearded', 'Bersee', 'Maris
Huntsman' and 'Maris Widgeon', grown in Germany in 1989. The asterisks indicate significant differences
between the original variety and their Rht lines (V-test)
Variety/
isogenic
line
Ear
emergence I
(days)
Tiller
number
(1 m)
Yield
of 20 ears
(g)
Plot
yield
(g)
Harvest
index
April Bearded
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
33.0
32.0"*"
33.0
33.0
33.0
33.0
48
54
49
56*
56*
58*
25.9
28.8
28.8
32.9**
29.1*
28.5
32.0
50
53
52
53
53
46
37.0
33.0"**
33.0"**
33.0*"'33.0***
33.0"**
33.0
33.0
33.0
35.0***
33.0
35.0""*
46
50
56
36
46
47
49.7
50.2
47.1
43.9*
44.6"
33.0**"
35.0
36.0***
35.0
35.0
35.0
35.0
33
47
45
45
46
41
39.9
39.4
42.7
35.5
35.4
31.0"
680
1050***
930"
1060"**
970"*"
860"
0.30
0.32
0.36**
0.45**"
0.39**
0.46***
Bersee
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
35.9
38.6
38.8
36.1
32.6*
910
960
910
900
910
690*
0.38
0.40
0.42*"
0.43**
0.45**
0.42*
M. Huntsman
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
930
1030
980
760
860
480***
0.47
0.51 **
0.49
0.50
0.52*
0.47
M. Widgeon
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
I
Days from 1st May
630
860
900*
760
760
600
0.37
0.42
0.43*
0.41
0.42
0.42
" = Significant at 5 % level
= Significant at 1 % level
*** = Significant at 0.1 % level
*"
Plant Breeding, Vol. 111 (3)
15
210
BORNER, WORLAND, PLASCHKE, SCHUMANN and LAW
erated days to flowering. The increase in the
number of days averaged 3.5 but varied with
seasons from less than two to seven days, with
the difference in 1989 being significantly higher than that recorded in the two following
seasons. This seasonal difference was probably
associated with temperatures at ear emergence
time that were lower in 1989, producing
slower ear emergence.
Secondary pleiotropic effects of Ppdl are
associated with the gene shortening the grow-
ing period. This was seen in all three seasons
by a reduction in plant height and in the
number of spikelets developed per ear. Height
reductions were significant in all three seasons
with an average reduction of around 4 em. The
level of reduction was highest in 1991. The
number of developed spikelets was also significantly reduced by Ppdl in all three seasons
with an average reduction of 1.25 spikelets.
The degree of reduction varied slightly with
the season.
Table 2. Effects of Rht alleles on yield components in near isogenic lines of 'April Bearded', 'Bersee', 'Maris
Huntsman' and 'Maris Widgeon', grown in Germany in 1990. The asterisks indicate significant differences
between the original variety and their Rht lines (V-test)
Variety/
isogenic
line
Ear
emergence!
(days)
Tiller
number
(1 m)
Yield
of 20 ears
(g)
Plot
yield
(g)
Harvest
index
April Bearded
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
21.0
21.0
21.8"*
22.5"**
22.7**"
23.0**"
139
152
150
133
141
111 *
34.7
42.0*
39.8
49.4"*"
47.1 ***
44.8"**
1570
1970*"*
1860*
2370***
2240"*"'
1880"*"
0.30
0.38**
0.34
0.41 **
0.44***
0.45***
22.0
21.0**
21.2***
22.5
22.0
22.3
161
124**
130
125"
121*
118*
50.2
55.9*
55.7
59.0*
57.8**
54.7*
2450
2790*
2800"
2460
2800*
2290
0.40
0.45
0.43
0.48*
0.48*
0.50***
21.0
22.7
21.3
22.0"**
22.2"**
22.3***
169
130*
146
115*"
126*
116''''
56.7
62.5*
64.2*
64.1*
60.2"
55.2
3310
3500
3500
2860*
3140
2120**"'
0.47
0.50*
0.53**
0.55***
0.55**
0.54*
22.8
22.0"*
22.3
22.0"
23.0
22.3
148
140
134
120"
136
122*
53.6
53.6
55.2
55.8
50.2
51.8
2340
2840***
2540"
2430
2340
1890**"
0.38
0.44**
0.45*
0.42**
0.43*
0.40
Bersee
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
M. Huntsman
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
M. Widgeon
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
1
Days from 1st May
*
**
)!-)I-*
= Significant at 5 % level
= Significant at 1 % level
= Significant at 0.1 % level
211
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
Although the early flowering genotypes
produce fewer spikelets in each season, the
grain setting in each of the remaining spikelets
was always significantly increased by an average of 0.29 grains. There was no seasonal
interaction with this improved spikelet fertility. In all three seasons the improved spikelet
fertility more than compensated for the reduction in spikelet number producing an overall
increase in grains per ear. This increase in
grains per ear varied over the seasons with the
average increase in number of grains per ear
promoted by Ppdl being three grains.
The spikelet and ear yields are dependent on
both the number of grains setting in the ear and
on the ability of the plant to fill these grains as
reflected by the 1000-grain weight. Over the
three years the presence of Ppdl only significantly increased grain weight in 1991. The
combination of both increased numbers of
Table 3. Effects of Rht alleles on yield components in near isogenic lines of 'April Bearded', 'Bersee', 'Maris
Huntsman' and 'Maris Widgeon', grown in Germany in 1991. The asterisks indicate significant differences
between the original variety and their Rht lines (V-test)
Variety/
isogenic
line
Ear
emergence!
(days)
Tiller
number
(1 m)
Yield
of 20 ears
(g)
Plot
yield
(g)
Harvest
index
April Bearded
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
53.6
54.2
54.2
54.2
54.3
53.7
0.44
0.39
0.40
0.38
0.45
0.45
31.2
39.6*
34.6
30.2
32.0
26.6
Bersee
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
51.2
50.8
51.0
50.5*
51.0
50.8
M. Huntsman
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
51.5
50.5
50.8
51.0
50.5*
51.2
51.0
50.3
51.0
50.7
50.7
51.0
84.2
80.3
81.7
87.8
58.5*"*
87.6
39.6
45.6
34.8
41.0
34.4
29.6*
2039
2120
1820
1830
1600"*
1460"''''
0.47
0.48
0.42
0.47
0.52"
0.49
107.2
104.5
98.8
101.0
95.5
106.2
43.8
40.8
38.4
39.8
37.0
36.2
2590
2570
2460
1780"**
2110''''
1430"**
0.50
0.52
0.49
0.52
0.51
0.47
110.3
107.5
102.3
89.8*
92.5
90.8
41.0
37.6
43.4
38.0
30.6*
31.0
2830
2470*
2510*
1660"*
1720**
1340**"
0.40
0.43
0.52"
0.47*
0.44
0.43
M. Widgeon
rht
Rhtl
Rht2
RhtJ
Rht1+2
Rht2+3
I
Days from 1st May
= Significant at 5 %
= Significant at 1 %
*** = Significant at 0.1 %
'f
*~:-
level
level
level
15*
212
BORNER, WORLAND, PLASCHKE, SCHUMANN
grains setting in the spikelet and ear, and improved grain weight resulted in the early genotypes showing annual significant increases in
spikelet yield and also increases in ear yield,
that were significant in the 1989 and 1990
seasons.
and
LAW
plant. Although ear yields associated with
Ppdl were always improved, the early flowering genotypes seemed to have a variable effect
on tillering showing a significant reduction in
the 1990 season. The effects of Ppdl on final
plot yield, therefore, varied, being significantly higher in 1989 and 1991 but lower due
to poor tillering in 1990. On average yield was
improved by 160 g per plot.
The final plot yield is dependent upon levels
of ear yield and on the tillering capacity of the
MEAN TEMPERATURE
0c
25r-'~-----=-=~=---=--~-=--==-=-=":'-_------=-------_
1989
20
~
~""""'"
:=
15 1-
,...................................................................................
10 1-
5
#
-...................................
"
I
:c
:~
·····_··1
1-..........................................................
.
Ol--'-+~-+-~+-'--i~-+-~+-~i--'--+~+-~+--'--+~-+-~+-~f-­
19.5.21.5.23.5.25.5.27.5.29.5.31.5. 2.6. 4.6. 6.6. 8.6. 10.6.12.6.14.6.16.6.
25
°c
1990
20
~
.
15
10
==
1-.............
6 1-
.................................................................•...............
-
-
.
.
0~-+~-I-~+--'---I~-1-~+-~!---'-+~-+-~f--'-+~-+-~+-~f­
7.5. 9.5. 11.5.13.5.15.5.17.5.19.5.21.5.23.5.25.5. 27.5.29.5. 31.5. 2.6. 4.6.
25'--:~-----------------------
20
~
..-..
.
·I················c=:
,.~,
.
15
10 1-......
. .......•..,
.
5
Ol--'--f-~-+-~+-'--i~-+-~+-~i--'--+~+-~+--'--+~-+-~+--'--if-J
7.6. 9.6. 11.6.13.6.15.6.17.6.19.6.21.6.23.6.25.6.27.6.29.6. 1.7. 3.7. 5.7.
Fig. 4. Mean temperatures 15 days before and after ear emergence measured daily over three years. The
arrows indicate the mean ear emergence times of experiment 1
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
213
Effects of Rht8
The additive effects of Rht8 indicated that this
gene produced the expected significant reduction in plant height but promoted few other
pleiotropic effects. Levels of reduction in plant
height associated with Rht8 varied over seasons from 2 to 5 cm. The reduction in plant
height was obtained with no significant detrimental effects on other plant characters with
the exception of a reduction in tillering recorded only in 1990. Although non-significant, final plot yields associated with Rht8
were always positive. Only plant height and
tiller number showed seasonal climatic interactions.
Interactions between Ppdl and Rht8
.-I(, - *
~'(
(S~~
The interactions between Ppdl and Rht8 were
determined for all measured characters in each
of the three seasons. The results showed no
significant interactions for any character (data
not shown). This illustrated that Ppdl acts
independently of Rht8 perhaps as a consequence of the latter gene having few pleiotropic effects on examined characters under
German conditions.
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The results obtained from three years trials
under German conditions show that the GA
insensitive dwarfing genes of wheat induced
major effects on plant height. Whereas the
percentage of reduction seemed to be independent of the genetical background and the
environment (years), the absolute plant height
was correlated to final plant height of the
respective recipient genotype.
It is known that conflicting results exist for
the pleiotropic effects of the GA insensitive
dwarfing genes. GALE et al. (1989), SIP et al.
(1988), B6RNER (1988) or ALLAN (1989) found
positive effects on grain yield, mainly due to an
increased number of grains per ear coupled
with a small increase or decrease of grain size.
On the other hand ALLAN (1986), KEYES and
SORRELLS (1989) or KERTESZ et al. (1991) found
only neutral or even negative effects of the Rht
genes on yield due to a large decrease in grain
SIze.
Because of these opposing results an increased sensitivity of Rht genotypes to envi-
214
ronmental stress was postulated. Whereas LAW
and WORLAND (1985) found that high temperatures between the flag leaf and ear emergence
stage may result in a decrease of fertility,
HOOGENDORN and GALE (1988) found that an
additional reduction of grain size was evident
when there was a temperature stress during
grain filling. Based on this knowledge the recording of the mean temperature data before
and after flowering time during the three
growing seasons was important (Fig. 4).
By analyzing the yield components it was
shown that in all three years the semi-dwarfs
realized a higher number of grains per ear
compared to the tall controls. Even most of the
extreme dwarfs (RhtJ, Rhtl+2, Rht2+3) had a
higher grain number. One reason could be that
moderate temperatures of between 12 and
20°C were recorded in each season during the
critical 10 days prior to ear emergence when
plants are stress susceptible. So there seems to
be no problems, under mid-German conditions, in the utilization of GA insensitive Rht
genes for increasing grain number. However it
must be remembered that negative effects on
grain weight associated with the dwarf or semidwarf habit were observed.
The relation between the two components,
grain number and grain weight (under particular environmental conditions), determined the
grain yield of the Rht genotypes. Primarily in
the year 1991 where the increase in grain
number was not as big as in the two previous
years and where late flowering led to a shorter
period of grain filling, the yield was down.
Tiller number and ear emergence time seemed
to be unaffected by the semi-dwarf genes.
Depending on the prevailing climatic conditions in Germany, the yielding ability of Rht
isogenics, seem to be intermediate between
those of the UK, where increases of grain
numbers always seemed to be sufficient to
compensate for any reduction in grain size
(GALE et al. 1989) and those in Southern European countries like Hungary, where increased
fertility of dwarf genotypes was insufficient to
compensate for the reduction in grain weight
(KERTESZ et al. 1991).
At present few GA insensitive dwarf wheat
varieties are grown in middle Europe. However plant breeders could successfully use Rhtl
or Rht2, particularly in combination with varietal backgrounds which allow either for the
BORNER, WORLAND, PLASCHKE, SCHUMANN and LAW
selection of 'Tall dwarfs', giving a better adaptability to climatic stress, or in combination
with high grain weight donors. Alternatively,
the utilization of weaker alleles of the GA
insensitive dwarfing genes, like that from
'Saitama 27' which show a lower susceptibility
to higher temperatures (WORLAND and PETROVIC 1988) could be recommended.
The results obtained from experiment 2 ,
showed that Ppdl has distinct advantages in
the breeding of high yielding winter wheats '
adapted to middle Europe. At the present time
most of the varieties grown in middle Europe
are day-length sensitive carriers of ppdl.
Switching to day-length insensitivity should
yield positive benefits by bringing forward
flowering time and permitting the plant to
develop and fill grains before the onset of hot
and dry summer conditions. In Yugoslavia for
example, the early flowering habit is associated
with a yield increase of at least 30 % (WORLANDet a1.1988, 1991).
The three negative pleiotropic effects of
Ppdl were reductions in height, tillering and
number of spikelets per ear. Reduction of
height can be beneficial effect if not correlated
with reductions in yield. A shorter plant is
more lodging resistant and would produce a
better harvest index with less energy being
required to develop vegetative growth being
available for redistribution to grain development. Reduced tillering is a disadvantage, but
if recognized in a variety can be compensated
for by increasing the recommended seed sowing rate. A reduction in spikelet number must
be regarded as a disadvantage. However in the
presence of Ppdl the reduced spikelet number
was more than compensated for by an increase
in spikelet fertility of around 13 % resulting in
a 7 % increase in the number of grains per ear.
Middle European conditions appear to favour
an improvement in seed development and grain
weight associated with the early flowering producing a 15 % improvement in spikelet yield
and 9 % improvement in ear yield. Therefore,
provided any problems associated with a reduced tillering capacity can be compensated
for, then Ppdl should give a yield advantage.
Over three seasons a yield advantage of around
9 % was recorded.
On its own Rht8 appears to offer little advantage to middle European breeding programmes providing only a slight reduction in
Pleiotropic Effects of Genes for Reduced Height and Day-Length Insensitivity
plant height without influencing other agronomic characters. Height reductions associated with Rht8 in middle Europe were less
than those obtained for similar genotypes
grown in the UK or Yugoslavia (WORLAND et
al. 1988).
Zusammenfassung
Pleiotropieeffekte von Genen fUr reduzierte
Pflanzenlange (Rht) und Tageslangen-Insensitivitat (Ppd) auf den Kornertrag und seine
Komponenten beim Weizen, angebaut in
Mitteleuropa
In Freilandexperimenten in Deutschland wahrend drei Vegetationsperioden wurden Pleiotropieeffekte auf den Kornertrag und seine
Komponenten analysiert. Untersucht wurden
vier Satze nahezu isogener Linien, welche die
GA insensitiven Kurzstrohgene/-alle1e Rhtl,
Rht2, RhtJ, Rht1+2, Rht2+3 oder rht (lang)
in vier verschiedenen genetischen Hintergriinden enthalten, sowie 24 Linien, rekombiniert
fur ein einzelnes Chromosom im genetischen
Hintergrund von 'Cappelle Desprez' und spaltend fiir das GA sensitive Kurzstrohgen Rht8
und das Gen fiir Tageslangenreaktion Ppdl.
Die GA insensitiven Kurzstrohlinien realisierten in allen drei J ahren eine hahere Kornzahl
pro Ahre bei einem geringeren Korngewicht.
In Abhangigkeit von den klimatischen Bedingungen der einze1nen Jahre konnte die geringere Kornmasse durch die erhahte Kornzahl
kompensiert und somit ein haherer Ertrag erreicht werden. Fiir das Gen Ppdl wurde ein
positiver Effekt auf den Ertrag unter den klimatischen Bedingungen von Mitte1europa
nachgewiesen.
The authors gratefully acknowledge Dr. M. MOHR
and Dr. R. FOCKE from the Institute of Cereal
Research Bernburg for conducting the field experiments.
References
I
ALLAN, R. E., 1986: Agronomic comparisons
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215
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BORNER
BORNER
et aI.,et Pleiotropic
aI., Pleiotropic
Effects
Effects
of Genes
of Genes
for Reduced
for Reduced
Height
Height
and Day-Length
and Day-Length
Insensitivity
Insensitivity
insensitive
dwarfing
the wheat
variety
dwarfing
genegene
fromfrom
the wheat
variety
SIP, SIP,
V., P.
V.,AMLER,
P. AMLER,
1. BOBKOVA,
L. BOBKOVA,
and and
M. SKORPIK,
M. SKORPIK, insensitive
27. Euphytica
27. Euphytica
38, 55-63.
38, 55-63.
Saitama
1988:1988:
Efficiency
Efficiency
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of early
generation
generation
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selection
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C. LAW,
N. LAW,
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Height
Height
Rht2Rht2
in ain Czechoslovak
a Czechoslovak
wheat
wheat
breeding
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to Yugoslavian
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genesgenes
and their
and their
importance
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gramme.
gramme.
Proc.Proc.
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Int. Int.
Wheat
Wheat
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winter
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Genetic
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2D of
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1. The
1. The
loca-loca- joprivreda
38, 245-258.
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joprivreda
38, 245-258.
of genes
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height,
day-length
insen-- - ,S. ,PETROVIC,
S. PETROVIC,
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C. N.
C. LAW,
N. LAW,
988: 988:
Genetic
Genetic
tion tion
of genes
affecting
height,
day-length
insenof chromosome
of chromosome
2D 2D
of wheat.
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II. The
II. The
sitivity,
hybrid
dwarfism
yellow
resist- analysis
analysis
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hybrid
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yellow
rust rust
resist96,331-345.
importance
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chromosome
chromosome
to Yugoslavian
to Yugoslavian
importance
Z. Pflanzenziichtg.
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Z. Pflanzenziichtg.
96, 331-345.
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The The
gibberellic
gibberellic
acid acid varieties.
247-259.
247-259.
varieties.
PlantPlant
Breeding
Breeding
100, 100,