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increase the selection efficiency. Genetic linkage maps that are essential to the detection of QTL and other applications have been constructed for nearly all economically important plants. Although there are a number of genetic maps reported in B. rapa

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Genetic linkage mapping has historically been the basis for genomic investigation and the analysis of quantitative trait loci (QTL) ( Doerge, 2002 ). The construction of a detailed linkage map is, in fact, the initial step for the use of genetic

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have made it possible to create genetic maps and exploit genetic linkage between markers and traits with unprecedented resolution. For example, SNPs identified by high-throughput sequencing serve as markers of the associations between genotypes and

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). Given that such inheritance can be traced in a genetic map that has been constructed based on linkage with the recombination rate, the genetic map is a solid foundation for genetic improvements in crop plants. More importantly, a consensus genetic map

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Garlic has been propagated exclusively by asexual means since time immemorial. The recent discovery of male fertile garlic accessions allowed studies on genetics and garlic improvement. Single nucleotide polymorphism (SNP) and random amplified polymorphic DNA (RAPD) based genetic linkage map was developed for garlic using a segregating population derived from one plant of PI 540316. Progenies segregated for male fertility and other morphological characters. Distortion of segregation was observed for most of the markers. This was expected due to the segregation of recessive deleterious alleles present in the garlic genome. The map contained 23 loci distributed on five linkage groups. It covered 319 cM with the average of 18 cM between loci. Linkage with the male fertility (Mf) locus was established with SNP marker AOB155 (26.7 cM).

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Random amplified polymorphic DNA (RAPD) markers were analyzed in parents and progeny of four sweetpotato crosses. An average of 69 primers were tested and 23.5% produced well resolved polymorphic banding patterns. Each polymorphic primer had an average of 1.9 polymorphic bands resulting in 0.45 polymorphic fragments per primer tested. Phenotypic segregation ratios of 88% of polymorphic fragments fit those expected for hexaploid Mendelian inheritance. Numbers of linked polymorphic fragments and numbers of linkage groups were 13 and 5 for Cross A, 0 and 0 for Cross B, 23 and 3 for Cross C and 16 and 6 for Cross D. Those results indicated that RAPD markers have potential for a genetic linkage map in sweetpotato; however, many primers must be screened.

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alleles and genes may be responsible for broad genetic resistance to P. capsici in the gene cluster found under the major QTL on chromosome 5 in different genetic backgrounds. Linkages of QTL between PC resistance and horticultural traits. There have

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Genetic linkage maps have been proposed as tools for crop improvement. We constructed a genetic linkage map of cucumber including RFLP, RAPD, isozyme, and disease resistance markers. The map was used to determine the number, magnitude of effects, and action of genes conditioning quantitatively inherited fruit-quality traits, including length, diameter, seed cavity size, and color. Traits were evaluated in a replicated field trial over 2 years. A mating design was employed to confirm putative trait loci across generations and estimate overall genetic variances for the quality traits. For some traits, gene number estimates were similar to previously published reports employing biometrical methods.

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We have constructed a genetic linkage map of peach consisting of RFLP, RAPD, and morphological markers, based on 78 F2 individuals derived from the self-fertilization of four F1 individuals originating from a cross between `New Jersey Pillar' and KV 77119. This progeny set was chosen because parental genotypes exhibit variation in canopy shape, fruit flesh color, and flower petal color, size, and number. The segregation of 81 markers comprised of RFLP, RAPD and morphological loci was analyzed. Low copy genomic and cDNA probes were used in the RFLP analysis. The current genetic map for the WV family contains 57 markers assigned to 9 linkage groups, which cover 520 cM of the peach nuclear genome. The average distance between two adjacent markers was 9 cM. Linkage was detected between Pillar (Pi) and double flowers (Dl). RFLP markers loosely linked to Pi, flesh color (Y), and white flower (W) loci were found. Twenty-four markers remain unassigned.

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Genetic linkage map is being constructed for watermelon based on a testcross population and an F2 population. The testcross map comprises 262 markers (RAPD, ISSR, AFLP, SSR and ASRP markers) and covers 1,350 cM. The map comprises 11 large linkage groups (50.7–155.2 cM), 5 medium-size linkage groups (37.5–46.2 cM), and 16 small linkage groups (4.2–31.4 cM). Most AFLP markers are clustered on two linkage regions, while all other marker types are randomly dispersed on the genome. Many of the markers in this study are skewed from the classical (Mendelian) segregation ratio of1:1 in the testcross or the 3:1 ratio in the F2 population. Although the skewed segregation, marker order appeared to be consistent in linkage groups of the testcross and F2 population. A cDNA library was constructed using RNA isolated from watermelon flesh 1 week (rapid cell division stage), 2 weeks (cell growth and storage deposition stage, 4 weeks (maturation stage), and 5 weeks (postmaturation stage) post pollination. Over 1,020 cDNA clones were sequenced, and were analyzed using the Basic Local Alignment Search Tool (BLAST). The sequenced cDNA clones were designated as expressed sequenced tag (EST) markers and will be used in mapping analysis of watermelon genome.

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