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J.F. Watson II and I.L. Goldman

The primary pigments in red beet are the betalains, which include the red-violet betacyanins and the yellow betaxanthins. The recent adoption of betalain pigments from red beet as an alternative to synthetic food dyes has heightened interest in genetic modification of pigment production. Dominant alleles at two tightly-linked loci (R and Y) condition production of betalain pigment in the beet plant; however, several alleles at the R locus influence pigment amount and distribution. A mutant phenotype, characterized by irregular sectors of blotchy red and white root color, arose spontaneously in the beet breeding nursery. The blotchy mutant plant was used in crosses with non-blotchy inbred lines to characterize its inheritance. Chisquare goodness-of-fi t tests of segregation data in backcross and F2 generations for several genetic backgrounds did not deviate from the hypothesis that a single recessive gene controls the blotchy phenotype. Linkage analysis was conducted to determine if the blotchy phenotype was conditioned by a new locus or an allele at a previously described locus. Our data indicate the bl gene resides at a newly described locus linked to R and Y. Maximum likelihood estimation revealed a linkage distance between R and Y of 8.95 ± 0.49 cM. The linkage distance between R and BL was calculated at 13.99 ± 1.18 cM, and the overall linkage between Y and BL was determined to be 28.8 ± 4.2 cM. Our data suggest the RYBL genomic region plays a critical role in the genetic control of betalain biosynthesis.

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Pere Arús, Carmen Olarte, Miguel Romero and Francisco Vargas

Ten isozyme genes were studied after analyzing the variability of eight enzyme systems—glucose phosphate isomerase (GPI), phosphoglucomutase (PGM), aspartate aminotransferase (AAT), leucine aminopeptidase (LAP), 6-phosphogluconate dehydrogenase (6PGD), isocitrate dehydrogenase (IDH), shikimate dehydrogenase (SDH), and aconitase (ACO)—in the progeny of five crosses among almond [Prunus amygdalus Batsch, syn. P. dulcis (Miller) D. A. Webb] cultivars. Six of these loci were found to be located in two linkage groups, one containing four loci (Pgm-2, Gpi-2, Aat-2, and Lap-1) and two more in the other (Idh-2 and Aat-1). Genetic configurations of pairs of loci specific to segregating F1 progeny of crosses between heterozygous parents were found in our data, for which we derived the estimate of the recombination fraction and its variance. Linkage data for the gene pairs that could be estimated in various crosses were used to obtain a joint estimation of the recombination fraction.

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John McCallum, Gail Timmerman-Vaughan, Tonya Frew and Adrian Russell

Developmental, environmental, and genetic factors affecting seed color were studied in the progeny of a cross between two white-flowered (aa) green cotyledon (ii) field peas (Pisum sativum L.): the pale large-seeded Marrowfat cultivar Primo and the greener small-seeded Prussian Blue OSU442-15. Changes in chlorophyll and carotenoid content during seed development of the parental genotypes were determined by high performance liquid chromatography analysis. Both cultivars accumulated similar pigment quantities per seed, but pigment loss was greater during maturation of `Primo'. Bleached and unbleached mature seed tissues also were compared for pigment composition. Lutein was the predominant pigment in bleached cotyledons of both cultivars. Only trace amounts of pheophytins were detected in unbleached seed. In both genotypes, chlorophyll A : B ratios were ≈1:1 in seed coats compared to 3:1 in cotyledons. Objective measurements of seed color in terms of luminance (lightness) and chrominance (hue and saturation) were made in YUV color space by video image analysis. Inheritance of seed color was studied in an F2 population derived from the `Primo' × `OSU442-15' cross and inbred descendants. Quantitative trait loci (QTL) for seed color were localized by interval mapping using a linkage map of 199 molecular markers spanning most of the genome and by bulked segregant analysis and selective genotyping. Four genomic regions affecting seed color were detected. A major gene accounting for 61% of the phenotypic variance in seed lightness (Y luminance component) was identified on linkage group V linked to r locus. Another major gene, which accounted for 56% of the phenotypic variance in seed hue (U chrominance component), was mapped to a linkage group containing group III and IV markers. A QTL with smaller effect on seed hue (U and V chrominance components) was detected on linkage group VII. Support for overdominant allelic interaction for a QTL on linkage group I, adjacent to the legumin locus Lg-J, was obtained by selective genotyping of the seed lightness distributional extremes.

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Jack E. Staub, Zhanyong Sun, Sang-Min Chung and Richard L. Lower

( ). Linkage analysis, segregation distortion tests, and map analysis. Linkage analyses were performed using MapMaker/EXP 3.0 ( Lander et al., 1987 ) and JoinMap 3.0 ( Van Ooijen

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R.O.M. Mwanga, A. Kriegner, J.C. Cervantes-Flores, D.P. Zhang, J.W. Moyer and G.C. Yencho

When sweetpotato chlorotic stunt crinivirus (SPCSV) and sweetpotato feathery mottle potyvirus (SPFMV) infect sweetpotato [Ipomoea batatas (L.) Lam.], they interact synergistically and cause sweetpotato virus disease (SPVD), a major constraint to food productivity in east Africa. The genetic basis of resistance to these diseases was investigated in 15 sweetpotato diallel families (1352 genotypes) in Uganda, and in two families of the same diallel at the International Potato Center (CIP), Lima, Peru. Graft inoculation with SPCSV and SPFMV resulted in severe SPVD symptoms in all the families in Uganda. The distribution of SPVD scores was skewed toward highly susceptible categories (SPVD scores 4 and 5), eliminating almost all the resistant genotypes (scores 1 and 2). Likewise, when two promising diallel families (`Tanzania' × `Bikilamaliya' and `Tanzania' × `Wagabolige') were graft inoculated with SPCSV and SPFMV at CIP, severe SPVD was observed in most of the progenies. Individual inoculation of these two families with SPCSV or SPFMV, and Mendelian segregation analysis for resistant vs. susceptible categories led us to hypothesize that resistance to SPCSV and SPFMV was conditioned by two separate recessive genes inherited in a hexasomic or tetradisomic manner. Subsequent molecular marker studies yielded two genetic markers associated with resistance to SPCSV and SPFMV. The AFLP and RAPD markers linked to SPCSV and SPFMV resistance explained 70% and 72% of the variation in resistance, respectively. We propose naming these genes as spcsv1 and spfmv1. Our results also suggest that, in the presence of both of these viruses, additional genes mediate oligogenic or multigenic horizontal (quantitative) effects in the progenies studied for resistance to SPVD.

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Rui Sun, Hui Li, Qiong Zhang, Dongmei Chen, Fengqiu Yang, Yongbo Zhao, Yi Wang, Yuepeng Han, Xinzhong Zhang and Zhenhai Han

-browning phenotype and all of the 50 seedlings with heavy-browning phenotype were used to construct the segregating population for linkage analysis of relevant major genes. Young leaves were sampled from each seedling of the segregating population in 2010. Total

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Richard Durham, Gloria Moore and Charles Guy

Genetic linkage analysis was performed on an interspecific backcross of citrus [Citrus grandis (L.) Osbeck cv. Thong Dee X (Thong Dee X Poncirus trifoliata (L.) Raf. cv. Pomeroy)], using restriction fragment length polymorphism (RFLP) and isozyme analysis. Sixty-five progeny were analyzed for a total of 57 segregating markers including 9 isozymes and 48 RFLPs. Significant (p = 0.05) deviation from an expected 1:1 segregation ratio was observed for 21 (37%) of the 57 loci, but this did not exclude their use in the mapping study. Linkage analysis revealed that 50 loci mapped to 12 linkage groups while 7 loci segregated independently from all other markers. The total map distance included in the 12 linkage groups was 472 cM with the mean distance between markers being 12.8 cM. This does not represent a saturation of the genome with markers; however, this work demonstrates the potential for mapping traits of economic importance in citrus.

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Benard Yada, Gina Brown-Guedira, Agnes Alajo, Gorrettie N. Ssemakula, Robert O.M. Mwanga and G. Craig Yencho

Genetic diversity is critical in sweetpotato improvement as it is the source of genes for desired genetic gains. Knowledge of the level of genetic diversity in a segregating family contributes to our understanding of the genetic diversity present in crosses and helps breeders to make selections for population improvement and cultivar release. Simple sequence repeat (SSR) markers have become widely used markers for diversity and linkage analysis in plants. In this study, we screened 405 sweetpotato SSR markers for polymorphism on the parents and progeny of a biparental cross of New Kawogo × Beauregard cultivars. Thereafter, we used the informative markers to analyze the diversity in this population. A total of 250 markers were polymorphic on the parents and selected progeny; of these, 133 were informative and used for diversity analysis. The polymorphic information content (PIC) values of the 133 markers ranged from 0.1 to 0.9 with an average of 0.7, an indication of high level of informativeness. The pairwise genetic distances among the progeny and parents ranged from 0.2 to 0.9, and they were grouped into five main clusters. The 133 SSR primers were informative and are recommended for use in sweetpotato diversity and linkage analysis.

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David C. Jarrell and Mikeal L. Roose

We report a preliminary genetic map of citrus based on segregation of 8 isozyme and at least 33 RFLP loci. The segregating population consisted of 60 plants from a cross of two citrus rootstock, `Sacaton' citrumelo × `Troyer' citrange. This cross represents an intergeneric F2 since `Sacaton' is Citrus paradisi (grapefruit) × Poncirus trifoliata (trifoliate orange) and `Troyer' is C. sinensis (sweet orange) × P. trifoliata. RFLPs were identified using anonymous probes from both cDNA and genomic DNA libraries of citrus. About 20% of the loci deviated significantly from Mendelian segregation. Two-point linkage analysis identified 8 linkage groups in which pairs of loci were within 30 centimorgans. This suggests that we have markers on most of the 9 chromosomes of Citrus. A map based on multipoint linkage estimates will be reported. Evidence for structural rearrangements between Citrus and Poncirus and extension of the map to additional marker and disease resistance loci will be discussed.

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Wayne Kennard, Arian Dijkhuizen, Michael Havey and Jack Staub

The analysis of genetic linkage in cucumber (Cucumis sativus has primarily involved morphological and disease resistance markers. Linkage analysis in cucumber would benefit from more markers. Restriction fragment length polymorphisms (RFLPs) can occur in relatively large numbers within a single segregating family. Research is presently underway to construct an RFLP map of cucumber. Pst I partial genomic and cDNA libraries of cucumber have been constructed as sources of probes for RFLP analysis. Cucumber DNA from 16 accessions of cucumber and one accession of C. sativus var. hardwickii were digested with either of two restriction enzymes (EcoR I and Hind III). This germplasm allows for the assessment of the variability for RFLPs in cucumber and will provide the parents for map construction.