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Pigments in orange carrot tissue, such alpha and beta carotene, are important vitamins in the human diet. Previously identified white or nonpigmented carrot roots, such as those from wild carrot and white derivatives of yellow or orange types, are dominant to the production of pigment, which is recessive. A nonpigmented carrot root was discovered during routine propagation of the inbred line W266 in 1992. Subsequent segregation analysis in the F2 and BC1 generations in three genetic backgrounds demonstrated the lack of pigmentation is due to a single recessive gene (reduced-pigment: rp). Total carotenoid content was reduced 92% in the roots of rprp genotypes compared to RPRP genotypes, however there were no differences in carotenoid content in leaves. Plants carrying rprp also exhibit white-speckled leaves during 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.
The effects of population density on shape and size of cylindrical red beet genotypes were evaluated in a field experiment during 1994 and 1995. Two F1 hybrids and two open-pollinated genotypes were planted in replicated trials consisting of three population densities. Yield, harvest weight, percent harvestable beets per plot, length, middle width, top width, bottom width, length × width, length to width ratio, and a shape index (SI) were measured on a sample of beet plants from each plot. The density × genotype interaction was nonsignificant for all 10 traits. Averaged over genotypes, significant differences among densities were found for harvest weight, percent harvestable beets per plot, length, middle width, and length × width. In general, greater harvest weights, a higher percentage of harvestable beets, and greater length, middle width, and length × width values were found at low density. Averaged over densities, significant differences among genotypes were measured for all 10 traits. The open-pollinated genotypes Cyndor and Cylindra exhibited lower yield, lower harvest weight, greater SI, and a higher percentage of harvestable beets than their hybrid counterparts. These data demonstrate that population density has a differential and significant effect on the shape and size of cylindrical beet genotypes.
A fasciated flower stem character arose spontaneously during development of the red beet (Beta vulgaris L.) inbred line W411. The fasciated character is manifest by a flattened flower stem with petioles coalesced into a twisted, ribbonlike appearance. No fasciation is present in the vegetative stem or petioles. An inheritance study was conducted to determine the genetic control of flower stem fasciation. The inbred line W411 was used both as a male and female parent in crosses with four red beet inbred lines. Segregating progenies in both the BC1 and F2 generations were developed and scored for the fasciated flower stem character. Variable expression of the fasciated flower stem phenotype was observed in these progenies; however, the presence of flattened flower stems at the stem-hypocotyl junction was unequivocal. Chisquare goodness-of-fit tests in the BC1 and F2 generations did not deviate significantly from expected ratios for a monogenic recessive character for each genetic background. No reciprocal differences were detected for any cross in this group of four inbred lines, which suggests the lack of maternal effect for the fasciated character. The symbol ffs is proposed to describe the genetic control of the fasciated flower stem phenotype.
Plant breeding is a process that is difficult to compress into laboratory exercises for the classroom. At the heart of plant breeding is the act of selection, a process whereby differential reproduction and survival leads to changes in gene frequency. Given the relatively short span of an academic semester, it has been difficult for students to gain experience with the practice of selection using plant materials. Nearly 15 years ago, P.H. Williams developed Wisconsin Fast Plants, a model system for teaching plant biology in a classroom setting. Wisconsin fast plants are rapid-cycling versions of various Brassica species amenable to a variety of genetic studies due to their short life cycle and ease of handling. This paper describes the development of a model system using Brassica rapa L. fast plants for teaching the cyclical selection process known as recurrent selection in the context of a course on plant breeding. The system allows for up to three cycles of recurrent selection during a single 15-week semester and enables students to gain experience in planting, selection, pollination, and seed harvest during each cycle. With appropriate trait choice, phenotypic changes resulting from selection can be visualized after just three cycles. Using the Fast Plant model, recurrent selection can be practiced successfully by students in the classroom.
Quantitative trait loci influencing morphological traits were identified by restriction fragment length polymorphism (RFLP) analysis in a population of recombinant inbred lines (RIL) derived from a cross of the cultivated tomato (Lycopersicon esculentum) with a related wild species (L. cheesmanii). One-hundred-thirty-two polymorphic RFLP loci spaced throughout the tomato genome were scored for 97 RIL families. Morphological traits, including plant height, fresh weight, node number, first flower-bearing node, leaf length at nodes three and four, and number of branches, were measured in replicated trials during 1991, 1992, and 1993. Significant (P ≤ 0.01 level) quantitative trait locus (QTL) associations of marker loci were identified for each trait. Lower plant height, more branches, and shorter internode length were generally associated with RFLP alleles from the L. cheesmanii parent. QTL with large effects on a majority of the morphological traits measured were detected at chromosomes 2, 3, and 4. Large additive effects were measured at significant marker loci for many of the traits measured. Several marker loci exhibited significant associations with numerous morphological traits, suggesting their possible linkage to genes controlling growth and development processes in Lycopersicon.
The genetics of resistance to root-knot nematode (M. hapla Chitwood) was studied in crosses of three carrot inbred genotypes, two resistant genotypes (R1 and R2) and one susceptible genotype (S1) identified in previous screening tests. Seedlings of three parental genotypes, six F1 crosses including three reciprocal crosses, two BC1 populations, and three F2 populations were evaluated for their resistance and susceptibility to infestation of M. hapla Chitwood based on gall number per root, gall rating per root, and root rating per root in a greenhouse experiment carried out in 1994. All six F1 plants were susceptible, which indicated a lack of heterosis for resistance in these F1s. The R1 × S1 cross segregated 3 susceptible: 1 resistant in the F2, 1 susceptible: 1 resistant in the BC1R1, and did not segregate in the BC1S1. The R1 × R2 cross yielded 44 susceptible: 36 resistant seedlings in the F2 (R1R2), and 48 susceptible: 32 resistant in the reciprocal cross of R1 and R2, both of which closely fit a 9: 7 ratio (P ≤ 0.001). These results indicate these two resistant genotypes carry two different homozygous recessive genes conditioning root-knot nematode resistance. We propose a model of duplicate recessive epistasis control the reactions of host plants and nematode in these crosses.
The root-knot nematode (M. hapla Chitwood) poses a threat to carrot (Daucus carota L.) production in the United States. Little information is available concerning the genetic control of nematode resistance in carrot. Crosses between two inbreds, a resistant genotype (R1) and susceptible genotype (S1) identified in previous screening tests of carrot were studied in the F2 and BC1 generations to determine the heritability of resistance to the root-knot nematode. Seedlings of F2 (R1/S1), BC1S1, and BC1R1 generations were evaluated for their responses to infestation of M. hapla Chitwood based on gall number per root, gall rating per root, and root rating per root in a greenhouse experiment conducted during 1994. Narrow-sense heritabilities were calculated according to the method of Warner (1952). Narrow-sense heritability was 0.16 for resistance based on gall number, 0.88 for resistance based on gall rating, and 0.78 for resistance based on root rating. This information may be of importance to geneticists and carrot breeders for the development of nematode-resistant carrot cultivars.
Governmental recommended allowances for folic acid have increased dramatically in recent years, especially for pregnant women. Red beet is an important vegetable source of folic acid; however, little is known about the extent of variation for native folic acid content in red beet genotypes. The objective of this investigation was to evaluate variation in folic acid content (FAC) among red beet hybrids (F1), inbred lines (IL), plant introductions (PI), and open-pollinated cultivars (OP). Eighteen genotypes, including 12 F1 and six OP, were evaluated in field experiments during both years. Averaged over years, highly significant differences among genotypes and between F1 and OP were detected. FAC ranged from 3.7 mg to 15.2 mg per gram dry weight. The FAC in OP was 13% higher than in F1. Thirty genotypes, including 13 IL and 17 PI, were evaluated in greenhouse experiments during 1993 and 1994. Highly significant differences among genotypes and between IL and PI were detected. FAC varied from 1.54 mg to 11.13 mg per gram dry weight. The FAC in IL was 43% higher than in PI. These results demonstrate an approximate 10-fold variation among red beet genotypes for FAC.