Download Inheritance of a Recessive Character Controlling

All four allozyme markers examined in
this study showed tetrasomic segregation.
Restriction fragment length polymorphism
(RFLP) analysis of chloroplast DNA revealed that A. kantoensis was recently derived from a diploid congener A. asa-grayi
(Ito 1992), which is morphologically distinct from A. kantoensis and is distributed
in southern Japan. These results suggest
that A. kantoensis may be derived from A.
asa-grayi. In Asteraceae, other examples of
tetrasomic inheritance are also known in
Haplopappus spinulosus (Hauber 1986), Coreopsis grandiflora var. longipes (Crawford
1984), and Aster hispidus (Maki, Masuda
and Inoue, in preparation). Tetrasomic inheritance appears to be more prevalent in
Asteraceae than was previously thought.
From the Department of Biology, Fukuoka University of
Education, 729-1 Akama, Munakata, Fukuoka, 811-41 Japan (Maki and Masuda), and the Department of Biology
and Herbarium, Faculty of Science, Shinshu University,
3-1-1 Asahi, Matsumoto, Nagano, 390 Japan (Inoue).
This project was partly supported by a grant-in-aide
from the Japanese Ministry of Education, Science and
Culture, and grants from the Tokyu Foundation for Better Environment and the Foundation of River and Watershed Environment Management. The authors are indebted to Drs. M. Ito, A. Soejima, T. Yahara, and Ms. T.
Nishino for helpful suggestions. Address all correspondence to M. Maki at the address above.
The Journal of Heredity 1996:87(5)
References
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Kuramoto N, Takenaka A, Washitani I, and Inoue K,
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Levin DA, 1983. Polyploidy and novelty in flowering
plants. Am Nat 122:1-25.
Maki M, Masuda M, and Inoue K, in press. Genetic diversity and hierarchical population structure of a rare
autotetraploid plant Aster kantoensis (Asteraceae). Am
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Mayo O, 1971. Rates of change in gene frequency in
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Moody ME, Mueller LD, and Soltis DE, 1993. Genetic
variation and random drift in autotetraploid populations. Genetics 134:649-657.
Odrzykoski U and Gottlieb LD, 1984. Duplications of
genes coding 6-phosphogluconate dehydrogenase in
Clarkia (Onagraceae) and their phylogenetic implications. Syst Bot 9.479-486.
Rieseberg LH and Doyle MF, 1989. Tetrasomic segregation in the naturally occurring autotetraploid Allium
neuii (Alliaceae). Hereditas 111:31-36.
Shiraishi S, 1988. Inheritance of isozyme variations in
Japanese black pine, Pinus thunbergii Parl Silvae Genetica 37:93-99.
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1983. Starch gel electrophoresis of ferns: a compilation
of grinding buffers, gel and electrode buffer, and staining schedules. Am Fern J 73:9-27.
or orange types have been dominant to the
production of pigment, which is recessive.
The primary pigments in orange carrot tissue are alpha and beta carotene. A reduced-pigment carrot root was discovered
during routine propagation of the inbred
line W266 in 1992. Subsequent segregation
analysis in the F2 and BC, generations in
three genetic backgrounds demonstrated
the reduction in pigmentation is due to a
single recessive gene. We propose the
symbol rp to describe the genetic control
of this "reduced-pigment" phenotype. Total
carotenoid content was reduced 92% in
rprp genotypes compared to RPRP genotypes. Plants carrying rprp also exhibit
white leaves during very early stages of development, suggesting rp has an effect on
leaf chlorophyll content. This character may
prove useful in dissecting the complex inheritance of carotenoids in carrot.
Carrot roots may exhibit a range of colors
including white, yellow, orange, red, and
purple (Banga 1964). Purple pigmentation
is due to the presence of anthocyanins,
whereas orange, red, and yellow pigmentation is due to carotenoids. The primary
carotenoids in orange carrot tissue are alpha and beta carotene (Laferriere and Gabelman 1968). The primary carotenoids in
yellow carrot tissue are xanthophylls
(Imam and Gabelman 1968). Carrot pigmentation is of particular interest for nutritional reasons since animals convert
beta carotene into provitamin A. Carrot
roots are an important source of vitamin
A in the human diet.
Soltis DE and Soltis PS, 1989. Tetrasomic inheritance in
All previously identified white or nonHeuchera micrantha (Saxifragaceae). J Hered 80:123-126.
pigmented carrot roots, such as those
Soltis DE and Soltis PS, 1993. Molecular data and the
Crawford DJ, 1984. Allozyme divergence and intraspefrom wild carrot and white derivatives of
cific variation in Coreopsis grandiflora (Compositae). dynamic nature of polyploidy. Crit Rev Plant Sci 12:
243-273.
yellow or orange types, have been domiSystBot 9:219-225.
nant to the production of pigment [reStebbins GL, 1971. Chromosomal evolution in higher
Goldbladtt P, 1980. Polyploidy in angiosperms: monoplants. London: Edward Arnold.
viewed in Buishand and Gabelman
cotyledons. In: Polyploidy (Lewis WH, ed). New York:
Plenum Press; 219-239.
Received May 17, 1995
(1979)]. Laferriere and Gabelman (1968)
Accepted January 16, 1996
Grant V, 1963. The origin of adaptations. New York: Coreported a single dominant gene conlumbia University Press.
Corresponding Editor: James L. Hamrick
trolled the absence of pigmentation, reHauber DP, 1986. Autotetraploidy in Haplopappus spisulting in white roots, in yellow X white
nulosus hybrids: evidence from natural synthetic tetcrosses. These workers also found three
raploids. Am J Bot 73:1593-1606.
dominant genes were responsible for the
Inoue K, Washitani I, Kuramoto N, and Takenaka A,
absence of pigmentation in white X or1994. Factors controlling the recruitment of Aster kanInheritance of a Recessive
toensis (Asteraceae). I. Breeding system and pollination
ange crosses. Light orange has also been
system. Plant Spec Biol 9:133-136.
Character Controlling
shown to be dominant to orange (Imam
Ito M, 1992. Phylogeny of Aster and the allies deduced
and Gabelman 1968). Kust (1970) described
Reduced
Carotenoid
by RFLP analysis of chloroplast DNA. SHINKA 2:79 (in
three
dominant alleles—Y, Y,, Y^—which
Japanese).
Pigmentation in Carrot
prevented the formation of orange color in
Ito M and Soejima A, 1995. Aster In: Flora of Japan Illb.
(Daucus carota L.)
root xylem tissue. Buishand and Gabelman
Angiospermae dicotyledoneae sympetalae (Iwatsuki K,
Yamazaki T, Boufford DE, and Ohba H, eds). Tokyo:
(1979) characterized the effects of the series
I. L. Goldman and D. N. Breitbach
Koudansha; 59-73.
of Y alleles on carotenoid content in phloem
JPRDBC (Japanese Plant Red Data Book Committee),
and xylem. The Y allele, which conditions
All previously identified white or nonpig1989. Japanese Red Data Book of Plants. Tokyo: Nature
lack of pigmentation (or white roots), was
Conservation Society of Japan.
mented carrot roots such as those from
dominant to orange which was considered
Krebs SL and Hancock JH, 1989. Tetrasomic inheritance
wild carrot and white derivatives of yellow
Bever JD and Felber F, 1991. The theoretical genetics
of autopolyploidy. Oxford Surv Evol Biol 7:185-217.
3 8 0 The Journal of Heredity 1996-87(5)
Table 1. Goodness-of-flt of the observed F, and BC, segregation data from three crosses to a monogenic
model for the inheritance of the reduced-pigment trait in carrot
Cross
Generation Pigmented
W255A X W266rp
W259A X W266rp
W267A X W266rp
[W266rp X (W259A X W266rp)]
[W266rp X (W255A X W266rp)]
[W266rp X (W267A X W266rp)]
F2
F2
F2
BC,
BC,
BC,
123
134
175
161
138
150
Reducedpigmented
Expected
ratio
42
49
53
132
142
131
124:41
138:45
175:53
146:146
140:140
140:140
0.032
0.470
0.370
2.880
0.057
1.290
.98
.55
.63
.10
.97
.27
' Probability of a larger \2.
yy. The presence of Kand Y2 always resulted
in white roots, again demonstrating the
dominance of lack of pigmentation.
Several white carrot roots were discovered during routine nursery propagation
of the inbred line W266 in 1992. These
roots were identical in shape and size to
their orange counterparts (W266), however their roots were white. The nonpigmented roots remained white during early
growth stages and developed a slight yellow color in the phloem and outer xylem
at maturity. The objective of this investigation was to study the inheritance of this
white phenotype via segregation analyses
in three genetic backgrounds.
Materials and Methods
Initial crosses of the nonpigmented carrot
plant (hereafter designated W266rp) were
performed, following vernalization of the
roots, in the greenhouse during the winter
of 1993. W266rp was used as the male parent in crosses to orange-root inbred lines
W255A, W259A, and VV267A. Each of the
three lines used as females possessed a
sterile cytoplasm. W266 also carries a sterile cytoplasm but has dominant alleles at
the nuclear restorer locus resulting in male
fertility. Pollination was performed in
greenhouse isolation cages using houseflies. F, plants were grown during the summer of 1993 at Randolph, Wisconsin. Caro-
tene analysis was performed on samples of
root tissue from VV266, W266rp, and their
hybrid according to methods described by
Simon and Wolff (1987). All F, roots were
orange. F, roots were harvested, vernalized, and either self-pollinated or backcrossed to W266rp during the winter of
1994. Due to nuclear restorer genes, F,
plants produced fertile flowers despite being derived from a female parent with a
sterile cytoplasm. F2 and BC, progenies
were planted in 3.6 m rows on May 1, 1995.
Carrot roots were harvested on July 7,
1995, and the presence/absence of pigmentation was scored visually on a minimum of
160 plants in each genetic background-generation combination. Chi-square goodnessof-fit tests were performed for each genetic
background-generation combination.
Results and Discussion
Chi-square goodness-of-fit tests revealed
the data closely fit expected ratios for a
monogenic character for each genetic
background-generation combination (Table 1). These data suggest the reduced
pigment phenotype is conditioned by a
single recessive gene. We propose the
Figure 1. (a) Reduced-pigment carrot root (left); normal pigmented carrot root (F 2 segregant of W259 x W266rp) (right), (b) Effect of the reduced-pigment character on
pigmentation of early leaves (left). Normal pigmented carrot leaves of identical maturity (F2 segregant of W259 x W266rp) (right).
Brief Communications 3 8 1
2500
'Si
20O0-
O
1500-
W266
W266ipip
W255 x W266ipp
Genotype
Figure 2. Total carotenoid content of carrot roots
from genotypes RPRP, rprp, and their hybrid. Bars indicate standard errors.
symbol rp to describe the genetic control
of this "reduced pigment" phenotype.
Roots from plants carrying rprp gradually changed from white xylem and phloem to a slight yellow tint in the phloem
and outer xylem (Figure 1). Mature roots
(120 days after planting) from plants carrying rprp were similar in size and shape
to orange roots of W266. Carotenoid pigmentation of these mature roots was detectable (Figure 2), indicating the presence of relatively small amounts of pigment in rprp as compared to RPRP plants.
Mature roots had a whitish-yellowish appearance and contained 141 jtg carotene/g
dry weight. By contrast, orange pigmented
roots of W266 contained nearly 1,800 (ig
carotene/g dry weight. Carotene content
increases sharply during early stages of
root growth and levels off during the growing season and during storage (Werner
1940). Pigmentation of the rprp genotype
followed this pattern, however, development of carotenoids was minimal compared to standard orange roots.
The first several leaves of plants carrying rprp were white or speckled with white
(Figure lb), indicating an effect of rp on
leaf chlorophyll content. This whitening
was not evident beyond the sixth leaf, suggesting the effect of rp is developmentally
regulated. Indeed, mature plants carrying
rprp cannot be differentiated from plants
carrying RPRP by the color of their foliage.
Reduction in carotenoid content is characteristic of many chlorophyll mutants because the absence of carotenoid pigments
renders chlorophyll susceptible to photooxidation (Aronoff 1966). Curiously, the
effect of rp continues to inhibit carotenoid
synthesis but not chlorophyll synthesis
during growth and development.
The finding of recessive alleles condi-
3 8 2 The Journal of Heredity 1996:87(5)
tioning nonpigmentation in carrot roots is
contrary to results reported by Buishand
and Gabelman (1978), Imam and Gabelman (1968), Kust (1970), and Laferriere
and Gabelman (1968), who all determined
that lack of pigmentation is controlled by
dominant alleles. Kust (1970) described an
epistatic relationship between the alleles
Y Y,, and Y2 with two pigment enhancing
alleles, 10 and 0. He hypothesized that the
number of 10 and 0 alleles had to be greater than the number of Y, Y,, and Y2 alleles
for the presence of orange root color. He
further suggested that the recessive genotype yyy,y,y2y2ioiooo should be white since
it did not have the dominant pigment enhancing alleles; however, no verification of
this hypothesis was ever provided.
Lack of agreement regarding recessiveness of nonpigmentation with the results
reported by numerous workers suggests
the lack of pigmentation in W266rp is perhaps due to a lesion in a carotenoid biosynthesis gene that has not yet been studied. Since mature roots from rprp plants
exhibit small amounts of beta carotene, rp
does not completely block carotenoid synthesis. This character may prove useful in
dissecting the complex inheritance of carotenoids in carrot.
From the Department of Horticulture, University of
Wisconsin-Madison, 1575 Linden Drive, Madison, Wl.
The Journal of Heredity 1996:87(5)
References
Aronoff S, 1966. The chlorophylls—an introductory survey. In: The chlorophylls (Vernon LP and Seely GR,
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Banga 0, 1964. Origin and distribution of the western
cultivated carrot. Genet Agraria 17:357-370.
Buishand JG and Gabelman WH, 1979. Investigations on
the inheritance of color and carotenoid content in
phloem and xylem of carrot roots (Daucus carota L).
Euphytica 28:611-632.
Imam MK and Gabelman WH, 1968. Inheritance ol a
number of phenotypes in Daucus carota L. (PhD dissertation). Madison, Wisconsin: University of Wisconsin.
Kust AF, 1970. Inheritance and differential formation of
color and associated pigments in xylem and phloem of
carrot, Daucus carota L. (PhD dissertation). Madison,
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Laferriere L and Gabelman WH, 1968. Inheritance of
color, total carotenoids, alphaorotene, and beta-carotene in carrots, Daucus carota L. Proc Am Soc Hort Sci
93:408-418.
Simon PW and Wolff XY, 1987. Carotenes in typical and
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Werner HO, 1940. Dry matter, sugar, and carotene content of morphological portions of carrots through the
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267-272.
Received August 1, 1995
Accepted December 31, 1995
Corresponding Editor: Kendall R- Lamkey
Inheritance of Kernel
Resistance to Fusarium
graminearum in Maize
C. Chungu, D. E. Mather, L. M.
Reid, and R. I. Hamilton
Inheritance of maize (Zea mays L ) kernel
resistance to ear rot caused by Fusarium
graminearum Schwabe was investigated
in generations derived from a cross between resistant (CO325) and susceptible
(CO265) maize inbred parents. Parents,
F,, F2, and backcross generations were
evaluated in two locations in eastern Canada in 1993 and 1994. Plants were inoculated with a macroconidial suspension
using a kernel-stab method 15 days after
silk emergence. Disease severity was assessed at harvest using a seven-class rating scale. Significant differences were observed among the generation means in all
environments. In general, the F, did not
differ significantly from the resistant parent
except at one location in 1993. The frequency distribution of the F2 and backcross generations showed continuous
variation. Generation means analysis indicated that resistance to F. graminearum
was under genetic control with both simple (additive and dominance) and digenic
(dominance x dominance) effects contributing to the total genetic variation among
the generation means. Weighted least
square regression indicated that more
than 68% of the genetic variation could be
explained by additive effects. Estimates of
the number of effective factors affecting
kernel resistance ranged from 4.6 to 13.7.
Fusarium graminearum Schwabe (sexual
state: Gibberella zeae Schwein) may enter
maize (Zea mays L.) ears via the silk or
through wounds made by insects or birds.
According to Koehler (1942), entry via the
silk and/or silk channel is the most common mode of entrance of many pathogens.
Plants may require different resistance
mechanisms to defend themselves against
different modes of fungal entry. Reid et al.
(1992a,c) have presented evidence for resistance in the silk tissue that acts by preventing the fungus from growing rapidly
down the silk to the kernels. However, genotypes possessing this resistance mechanism may not have any means of inhibiting the spread of the fungus from kernel
to kernel should the fungus bypass the
silk or succeed in overcoming the silk resistance. Resistance mechanisms in the