Brief Communications
carrots (Harborne 1976). In some carrots,
anthocyanin pigmentation confers a more
red color, so other pigments may be involved.
The genetics of purple pigmentation in
P. W. Simon
carrots has received some attention. Purple petiole found in 'Tendersweet' was
Inheritance of purple and yellow storage
found to be conditioned by one locus with
root pigmentation was studied in F2 and
purple, G, dominant to green, g (Angell
BC generations derived from carrot plant
and Gabelman 1970). In one study of carintroductions. Purple and yellow root colotene genetics, purple root color was notors were each conditioned by single domed in the F, progeny of two non-purple ininant loci, P, and Y2 . P, is described for
breds and thought to be conditioned by
the first time. Differences in expressivity of
two complementary loci (Laferriere and
P, were noted within storage roots and
Gabelman 1968).
throughout the plant. Purple root and flowOrange root color in carrot is thought
er pigmentation were inherited together in
to have originated in Northern Europe
derivatives of PI 173687, but PI 175719
(Banga 1957). The inheritance of storage
purple-rooted derivatives had no purple
root carotenoid content and distribution
flower pigmentation. This suggests two
has been described (Buishand and Gabeldifferent alleles of P,. Purple node color
man 1979). Several loci were named, inwas conditioned by a second locus, P2,
cluding Y, Y, and Y2, which influence the
which was linked to P, and separated by
amount and distribution of a- and (J-caroapproximately 36 cM. Purple leaves, petitene. The Y locus blocks synthesis of aoles, and bracts tended to be inherited toand 3-carotene as well as xanthophylls,
gether and independently of root pigmenwhereas y, and Y2 block synthesis of cartation. V2, which has been described preotenes but not xanthophylls (Buishand
viously, conditioned low carotene content
and Gabelman 1979).
of the storage root xylem ("core") in high
The purpose of this study was to invescarotene orange background whereas in
tigate the inheritance of purple and yellow
lower carotene orange background the
storage root pigmentation in carrot, to
yellow appearance often spread into phlorecord purple pigmentation occurring in
em. P, and Y2 were not linked to each oth- other plant parts, and to evaluate linkage
er or to Rs.
relationships with Rs, a monogenic trait
conditioning storage root sugar type
Purple root color occurs in wild Daucus
(Freeman and Simon 1983).
carota L. and has been known in domesticated carrots since before the tenth cenMaterials and Methods
tury (Banga 1957). This character is uncommon in cultivated Western carrots to- Carrot seed samples were obtained from
day, but some local varieties in the Mid- the Daucus collection of the USDA Regioneast and Asia, notably China and India, are
al Plant Introduction Station in Ames,
purple. Some of these varieties are in- Iowa, and grown in muck soil in Palmyra,
tensely purple and referred to as "black" Wisconsin. Purple root pigmentation was
carrots in India, where they account for
observed in many Plant Introductions, inless than 5% of the carrot crop.
cluding PI 173687 (Turkey), PI 175719
The cyanidin glycosides are known to
(Turkey), and PI 220285 (Afghanistan).
account for purple root color in "black" Root color due to carotenoids in these
Inheritance and Expression
of Purple and Yellow Storage
Root Color in Carrot
three Plant Introductions segregated and
included white, yellow, and orange forms
(white and yellow only for PI 220285) each
with and without anthocyanin purple. Yellow, orange, purple yellow, and purple orange-rooted plants were self-pollinated
three generations. In most cases, white or
purple white-rooted plants were weak and
not studied further.
To study the inheritance of purple root
color, individual plants with purple roots
from S3 populations (three generations of
self-pollination) true-breeding for root color from all three P.I.s were intercrossed
with orange-rooted USDA inbreds B493,
B9304, and B10138 which involved at least
six generations of self-pollination in their
development (Simon et al. 1990). To study
the inheritance of yellow root color, individual plants from the S3 populations from
PI 173687 which were true-breeding for
yellow root color, were also intercrossed
to these three USDA carrot inbreds as well
as with HCM (Simon and Wolff 1987).
B9304 and B10138 have typical orange
roots with carotene content of 90-150
ppm, whereas B493 and HCM are dark orange high-carotene inbreds (190-250 ppm
and 430-490 ppm carotenes, respectively)
(Simon and Wolff 1987). Color segregation
was observed in S,, S2, and S3 generations
of the Plant Introductions and in F,, F2, and
F3 generations of the (P.I.) X (inbred)
crosses as well as BC, crosses to the orange inbreds.
Tests of allelism were made among purple, orange, and yellow-rooted selections
from each of the Pi's as well as orange PI
x orange inbred crosses. For tests of allelism for purple root color, plants of selected nonsegregating purple-rooted S3 derivatives from each of the three plant introductions were intercrossed and root
color observed in resulting F2 populations.
For tests of allelism for orange root color,
individual plants from true-breeding orange-rooted S3 populations from PI 173687
and PI 175719 were crossed to each other
63
Table 1. Segregation of purple root color in carrot
of
PI 173687 S3
PI 175719 S3
PI 220285 S3
Ex-
NonPurple purple Total
Het.
X2
pected Seg.
ratio
X2
F2
BC
10
6
11
3
F2
BC
974
247
716
147
333
176
339
240
244
155
104
181
1,313
487
960
302
437
357
1.62
1.58
0.59
0.11
0.60
0.52
3:
1:
3:
1:
3:
1:
5
3
2
3
368
104
210
119
117
98
80
108
485
202
290
227
2.30
0.49
0.71
0.44
3:
1:
3:1
1:1
Cross
Gen
PI X B493
and reciprocal
PI x B10138
and reciprocal
PI X B9304
F2
BC
PI X B493
and reciprocal
PI X B493
Number of progeny
families
CO CM
Purple
parent
BC
F2
BC
0.47
0.10
0.09
0.21
0.34
0.07
0.20
0.18
1.03
0.53
P
.4-.5
.7-.8
.7-.8
,5-.7
.5-.7
,7-.8
.5-.7
.5-.7
,3-.5
.3-.5
pected 3:1 or 1:1 ratio (Mather 1938). Linkage intensities were calculated by the
product formula (Immer 1930) with the
formula bc/ad for coupling where a =
number of individuals carrying dominant
alleles at both loci (A-B-), b = number of
individuals carrying a dominant allele only
for the A locus (A-bti), c = number of individuals carrying a dominant allele only
for the B locus (qaB-) and d = the number
of individuals homozygous recessive at
both loci (aabb).
Results and Discussion
and to the two USDA carrot inbreds, B493
and B9304. Yellow-rooted plants from truebreeding S3 populations of the three plant
introductions were also intercrossed and
root color was observed in the resulting
F2 populations. At least three different F2
populations were evaluated for each
cross. To determine allelism of the yellow
root locus in this study, with a previously
described yellow carrot, four S3 plants
with yellow roots of PI 173687 were
crossed with four plants of Rheinische, an
open-pollinated yellow-rooted cultivar
from Horticultural Research International,
Wellesbourne, Warwick, U.K. Buishand
and Gabelman (1979) had determined that
this cultivar had a genetic constitution of
Y2Y2.
Purple (Table 1), yellow, and orange
(Table 3) pigmentation was examined in
storage root xylem and phloem of harvested roots. Additionally, purple or red
coloration was examined in nodes, peti-
oles, leaves, anthers, petals, and bracts of
flowering plants (Table 2).
To evaluate linkage of purple and yellow
root pigmentation to another monogenic
trait, high reducing sugar {Rs, versus high
sucrose, rs) content (Freeman and Simon
1983; Simon and Freeman 1985) was evaluated in segregating populations (Table
4). The F2 and BC data were analyzed using the x2 method to test the ratios expected for each character. Data were
pooled when the x2 value for heterogeneity indicated that families were homogeneous. The x2 test of independence (by orthogonal functions) was used to detect
linkage relations when data of all the single families in each pairwise group fit the
single factor segregation. Contingency x2
makes no prior assumptions about segregation ratios and was the preferred method for the disturbed single factor ratios
since segregation of some traits in some
families differed significantly from the ex-
Table 2. Purple color In roots, flowers, and nodes of F, carrot populations derived from two plant
introductions
Number of F2 plants
Purple color
Root
Rower
Node
PI 173687 X B493
derivatives
PI 175719 X B493
derivatives
321
0
0
102
40
0
0
87
0
0
0
0
76
64
21
21
Segregation x2 (P)
Purple roots (P,)
Purple nodes ( / y
0.09 (.7-.8)
1.91 (.1-.2)
0.46 (.9-.95)
6.52 (.01-.02)
Heterogeneity x2 (three families for each P.I.)
Purple roots (/>,)
Purple nodes (PJ
0.47
1.69
0.69
1.98
Linkage x2 (.P)
Crossover percentage
andSE
6 4 The Journal of Heredity 1996:87(1)
35.6(01-001)
14.0 (.01-.0001)
35 + 3
37 ± 6
Inheritance and Expression of Purple
Root Color
All F, hybrids between purple-rooted S3 inbreds derived from Plant Introductions
and orange-rooted USDA inbreds (which
lack purple) had purple pigmentation. Purple storage root pigmentation was conditioned by a single dominant gene in derivatives of the three carrot introductions examined (Table 1). The locus for purple
root pigmentation is designated f,. Both F2
and BC families were homogeneous for P,
(Table 1). Inbreeding depression was most
severe in PI 220285 derivatives, as reflected in plant vigor and seed productivity,
but segregation patterns for P, still fit expected ratios.
Genetic evaluation was usually unambiguous for purple root color. Tests of allelism indicated the same locus segregating in all three plant introductions since
all F2 populations derived from crosses between P.I.'s were 100% purple-rooted (data
not presented). This suggests a common
origin of purple root color locus in the
Turkish and Afghanistani carrots.
Expressivity of the P, locus in carrot
roots was sometimes variable. Typical P,/_
roots were pigmented in the outer quarter
of the phloem over the entire length of the
root except the tip 5-10 mm, which had
very little anthocyanin pigmentation. Purple pigmentation was very evident in phloem tissue near the storage root surface in
approximately 90% of the f,/_ roots examined. In these roots anthocyanin pigmentation rarely occurred throughout the
entire phloem to the vascular cambium,
and only a few roots had any purple color
in the xylem (although other carrot Plant
Introductions do have noticeably purple
xylem). In approximately 10% of the />,/.
roots examined, purple pigmentation was
discontinuous in the outer phloem, presenting a mottled appearance. The incidence of mottled roots was similar in derivatives of all three P.I.'s. In rare cases
Table 3. Segregation of yellow root color in carrot
Number of progeny
Yellow
core
Yellow
parent
PI 173687 S3
Cross
Gen
PI X B493
and reciprocal
PI x B10138
and reciprocal
PI x B9304
F2
BC
PI X HCM
F2
F2
BC
F2
BC
No. of
families
Orange
phloem
Yellow
phloem
Orange
Total
7
4
6
2
1
2
2
500
156
60
259
94
135
180
4
196
181
102
110
44
162
47
852
407
427
233
206
357
203
166
66
29
27
15
152
Het.
X2
Expected Seg.
ratio"
X2
P
12.21
9.66*
1.74
0.98
3:1
1:1
3:1
1:1
3:1
1:1
3:1
.1-2
.02-.05
.5-.7
.3-.5
.2-.30
.05-.10
.5-.7
1.21
1.43
1.81
4.96
0.28
0.72
1.46
3.05
0.37
P < .05.
Ratio ol yellow core/orange.
root anthocyanin pigmentation was restricted to one or two bands of purple less
than one square centimeter, based on examinations of 5-7-mm cross-sectioned
slices over the entire root. Even with such
a small amount of pigmentation, other
plant parts were often well-pigmented and
purple progenies were always found, often
with dark purple root color. Low-pigmented, mottled roots were either PJ F, or PJ
p,, based on progeny tests, and individual
family ratios were not different from expected 1:0 or 3:1 monogenic patterns.
Plants with mottled roots were more often
heterozygous but homozygous true-breeding mottled lines were noted.
Expression of P, was usually completely
dominant. A dark purple F5 derivative of
(PI 173687-S3 x B10138) denoted B7262
was crossed with 14 orange-rooted inbreds (which lack purple pigmentation)
derived from a broad range of carrot germplasm and yielded slightly mottled or uniformly purple-rooted progeny in most
cases (data not presented). One exception
was the hybrid with B4367 which had very
little purple pigmentation, to suggest the
presence of inhibitor loci.
Beyond root anthocyanin pigmentation,
P, conditioned the expression of pink corolla and purple or red anther pigmenta-
tion in derivatives of PI 173687 but not PI
175719 (Table 2). This indicates two different alleles at the f, locus. Floral pigmentation also varied widely in intensity,
independently of root pigment intensity.
Nonpurple F2 roots (all found to be pJ p,
in F3, as expected) never had purple floral
parts.
Both purple- and nonpurple-rooted carrots, when self-pollinated, had some progeny with pigmented nodes (Table 2). The
overall segregation for purple node pigmentation fit a monogenic model for PI
173687 derivatives but segregation was
disturbed in derivatives of PI 175719. This
locus, designated P2, was homogeneous in
expression among the small numbers
(three) of F2 families for each cross. P2 was
found to be linked to P, and separated by
approximately 36 cM (Table 2). Estimates
of linkage distance should be considered
as preliminary since P2 had disturbed segregation ratios in PI 175719 derivatives.
Leaf, bract, and petiole pigmentation accompanied node pigmentation but often
was more difficult to score with certainty
in mature plants. Perhaps this pigmentation was conditioned by the G locus (Angell and Gabelman, 1970), but genetic
stocks from these earlier studies were not
available. Purple pigmentation has also
Table 4. Test for linkage of carrot root characteristics: purple (P,), yellow (KJ, and high reducing sugar
(Rs)
Combinations
Gen.
F2
BC
RsY2
F2
BC
Pfis
BC
No.
of
families
7
3
9
3
No. of F2 orBC plants
Linkage
a
b
c
d
Total
Het. x2
X2
P
233
47
63
50
75
46
22
53
393
196
10.96
1.41
1.49
0.60
.5-.7
.8-.9
250
45
96
36
89
36
24
45
459
162
16.55*
3.57
2.30
1.60
,5-.7
.5-.7
222
42
84
39
91
29
20
44
417
154
6.37
3.30
4.59
3.40
,2-.3
.3-.5
been noted in sun-exposed roots ("sunred"), tissue culture, and mineral deficient
plants but expression under these conditions was not evaluated in this study. Purple center umbellet is also observed in
carrot and other Umbelliferae flowers but
did not occur in the materials evaluated.
Inheritance and Expression of Yellow
Root Color
The F, hybrids between yellow-rooted S3
inbreds and orange-rooted USDA inbreds
all had yellow xylem ("cores"). The phloem was orange in hybrids with B493 and
HCM, the high carotene inbreds, whereas
it was yellow in hybrids with B9304 and
B10138. These phenotypes are equivalent
to the "orange-yellow tinge" and "yellow"
color categories, respectively, described
by Buishand and Gabelman (1979).
All yellow-cored F2 and BC progeny were
categorized as Y2 /_ whereas orange-cored
progeny were categorized as y2 /y2. With
this, Y2 behaved as a simply-inherited dominant locus as reported by Buishand and
Gabelman (1979). Y2 tended to have higher
segregation and heterogeneity x2 values
than for />, and was not homogeneous
among F2 families derived from crosses
with B493 (Table 3). This is likely related
to the variation in expressivity of Y2 in different backgrounds. The yellow core, yellow phloem phenotype predominated in
derivatives of crosses with typical orange
inbreds (B10138 and B9304) whereas the
yellow core, orange phloem phenotype predominated in derivatives of the crosses
with B493 and HCM, dark orange inbreds.
As expected, root color in F3 and F4 families
derived from K2/_ F2 plants either segregated 3:1 yellow core/orange core or were
true-breeding for yellow cores. Among truebreeding families expressivity in phloem
color varied among and within families but
Brief Communications 6 5
the yellow core phenotype was stable (data
not presented).
All tests of allelism among yellow-rooted
inbreds from the three plant introductions
yielded 100% yellow-rooted F2 progeny. Intensity of yellow pigmentation varied and
approximately 11% white cores were observed in PI 175719 X PI 220285 progeny
but no orange progeny were observed in
any cross. The fact that PI 173687 X Rheinische F2 progeny were all yellow-rooted indicated that yellow root color was conditioned by Y2 since Rheinische derivatives
were found to be be Y2 /Y2 by Buishand
and Gabelman (1979).
As expected, orange root color (xylem
and phloem) was observed in all F2 progeny from intercrosses of orange-rooted S3
plants of PI 173687 x PI 175719 and also
F2 progeny from derivatives of these Pi's
X B9304, B10138, and B493 (data not presented). This indicates a genotype of y2 /
y2 for all orange inbreds evaluated.
The expression of Y2 in this study exhibited clear differences in the relative incidence of yellow phloem in derivatives
from different typical orange parents. This
was not noted by Buishand and Gabelman
(1979). Further examination of expressivity and penetrance of Y2 in various backgrounds and environments would be of interest.
The inheritance of carotene pigmentation was not investigated in derivatives of
PI 175719 or PI 220285 because of difficulty
in scoring carotene phenotype which was
compounded by inbreeding depression,
especially in white-rooted segregants. The
intense inbreeding depression was an unexpected result since purple-rooted and
yellow-rooted inbreds were able to be developed. The relationship between white
root color and inbreeding depression warrants further study.
Linkage was tested in several PI 173687
derivatives (Table 4). No linkage was
found between Pu Y2, and Rs. Both F2 and
BC families were homogeneous. Heterogeneity was generally higher in K, combinations and significant for Rs-Y2 F2's.
The diversity found in carrot Plant Introductions from Turkey in this study supports the hypothesis that Turkey is a secondary center of origin for Daucus (Vavilov 1992). Of particular interest is the occurrence of orange roots from both Plant
Introductions examined in this study and
in 37 of 72 other Turkish PL's in the USDA
collection. The y2 allele could have been
introduced into Turkey after its selection
in Northern Europe (Banga 1957) since
both of these Turkish P.I.s appear to be
6 6 The Journal of Heredity 1996:87(1)
domesticated carrots with segregants for
conical and cylindrical root shape typical
of European "Danvers" and "Nantes." The
co-occurrence of purple and orange root
color is interesting since these traits are
thought to have originated in the East and
West, respectively.
The Pt locus may be of use in carrot genetic and breeding studies. Evaluation of
purple root pigmentation was relatively
unambiguous and simple in many genetic
backgrounds. The evidence for two different P, alleles in the two P.I.'s from Turkey
as well as the occurrence of a second locus, P2, suggests a complex genetic basis
for anthocyanin pigmentation in carrot.
Based on studies in maize, snapdragon,
petunia, and other crops, other loci conditioning purple pigmentation may be expected to occur in carrot. Similarly, a better understanding of carotene biosynthesis may be gained from true-breeding orange- and yellow-rooted genetic stocks.
From the USDA, ARS Vegetable Crops Research Unit,
Department of Horticulture, University of Wisconsin,
1575 Linden Drive, Madison, WI 53706.
The Journal of Heredity 1996:87(1)
References
Angell FF and Gabelman WH, 1970. Inheritance of purple petiole in carrot, Daucus carota var. sativa. HortScience 5:175-176.
Banga 0, 1957. Origin and distribution of the European
cultivated carrot. Euphytica 6:54-63.
Buishand JG and Gabelman WH, 1979. Investigations of
the inheritance of color and carotenoid content in
phloem and xylem of carrot roots (Daucus carota L.).
Euphytica 28:611-632.
Freeman RE and Simon PW, 1983. Evidence lor simple
genetic control of sugar type in carrot (Daucus carota
L). J Am Soc Hort Sci 108:50-54.
Harborne JB, 1976. A unique pattern of anthocyanins
in Daucus carota and other Umbelliferae. Biochem Sys
Ecol 4:31-35.
lmmer RF, 1930. Formulae and tables for calculating
linkage intensities. Genetics 15:81-98.
Laferriere L and Gabelman WH, 1968. Inheritance of
color, total carotenoids, alpha-carotene, and beta-carotene in carrots, Daucus carota L. Proc Am Soc Hort Sci
93:408-418.
Mather K, 1938. The measurement of linkage in heredity. London: Methuen.
Simon PW and Freeman RE, 1985. A rapid method for
screening reducing sugar in carrot roots. HortScience
20:133-134.
Simon PW, Peterson CE, and Gabelman WH, 1990. B493
and B9304, Carrot inbreds for use in breeding, genetics
and tissue culture. HortScience 25:815.
Simon PW and Wolff XY, 1987. Carotenes in typical and
dark orange carrots. J Agric Food Chem 35:1017-1022.
Vavilov NE, 1992. Origin and geography of cultivated
plants. Cambridge: Cambridge University Press.
Received August 15, 1994
Accepted July 7, 1995
Corresponding Editor: James Hamrick
A Recessive Homeotic
Mutant in Pearl Millet
J. P. Wilson
A phylloid homeotic mutant was observed
and selected from a segregating breeding
population of pearl millet. Segregation of
panicle phenotype fit a 3:1 normal/mutant
ratio in F2 progeny and 1:1 normal/mutant
ratio in testcross progeny. The mutant phenotype was controlled by a single recessive allele, designated phm. The mutant
phenotype is expressed by plants in field
and greenhouse environments. The genetic stock can be used as an easily identifiable marker in linkage studies and in
studies of floral morphogenesis in pearl
millet.
Pearl millet [Pennisetum glaucum (L.) R.
Br, formerly P. typhoides (Burm.) Stapf et
Hubb., and P. americanum (L.) K. Schum.]
is a useful organism for genetic studies.
Spaced plants tiller profusely, and can be
easily selfed and cross-pollinated, to produce hundreds of seeds on each panicle.
The inheritance of many traits of pearl
millet has been examined, and summarized by Koduru and Rao (1983) and Kumar and Andrews (1993). Traits described
include chlorophyll-deficient mutations,
foliage mutants, pigmentation mutants,
panicle characteristics, meiotic mutations,
disease resistance, height, and maturity.
In the summer of 1992, a plant with a
proliferation of rudimentary leaves and
panicles developing from the florets on
the primary panicles was observed in a
segregating breeding population of pearl
millet. The objective of this study was to
determine the genetic basis and mode of
inheritance of this mutant phenotype.
Materials and Methods
A single plant with leaves and poorly developed panicles developing from the florets on the main panicles was observed
among —3,000 progeny in a breeding population in 1992. The population in which it
occurred was comprised of S, progeny of
a single plant derived from a recurrent selection breeding program that was initially
developed with 10 different breeding lines.
The rest of the plant was normal in appearance except for the panicles. The
plant had already cross pollinated when it
was observed. A few immature seeds were
present on the panicles, and panicles were
bagged to prevent loss of seed from bird
and insect feeding. Mature seeds were har-