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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 Allard RW, 1960. Principles of plant breeding. New York: John Wiley & Sons. Barrett SCH and Kohn JR, 1991. Genetic and evolutionary consequences of small population size in plants: implications for conservation. In: Genetics and conservation of rare plants (Falk DA and Holginger KE, eds). Oxford: Oxford University Press; 3-30. of isozyme markers in the highbush blueberry, Vaccinium corymbosum L. Heredity 63:11-18. Kuramoto N, 1983. Landscape diversity in the floodplain of the Tama River. J Japan Inst Landscape Arch 46:117-122 (in Japanese with English summary). Kuramoto N, 1984. Zonation of thefloodplainvegetation of the River Tama and its alteration by human activities. J Japan Inst Landscape Arch 47:257-262 (in Japanese with English summary). Kuramoto N, 1987. Vegetation changes and their causes in thefloodplainof the River Tama. Appl Phyto Sociol 16:13-23 (in Japanese with English summary). Kuramoto N and Sone N, 1985. Vegetation conservation and land-use in thefloodplainof the River Tama. J Japan Inst Landscape Arch 48:169-174 (in Japanese with English summary). Kuramoto N, Takenaka A, Washitani I, and Inoue K, 1992. A conservation biology of Aster kantoensis growing along the Tama River. J Japan Inst Landscape Arch 55:199-204 (in Japanese with English summary). 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 J Bot. Mayo O, 1971. Rates of change in gene frequency in tetrasomic organisms. Genetica 42:329-337. 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. Soltis DE, Haufler CH, Darrow DC, and Gastony GJ, 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, eds). New York: Academic Press; 3-20. 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, Wisconsin: University of Wisconsin. 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 dark orange carrots. J Agric Food Chem 35:1017-1022. Werner HO, 1940. Dry matter, sugar, and carotene content of morphological portions of carrots through the growing and storage season. Proc Am Soc Hort Sci 38: 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