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  • Author or Editor: R. Monet x
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Flow cytometric analysis, of leaf nuclei from three cultivars, was used to estimate the DNA content of peach (∼0.61 pg or ∼0.59 × 109 bp/diploid nucleus; 2x=16), and ndicated that the peach genome is only slightly larger than that of Arabidopsis. This value was indirectly confirmed by measurements of nuclei from haploid, triploid and “tetraploid” (cytochimera) peach accessions. cDNA and genomic clones have been used to determine the level of polymorphism among various peach cultivars and related species. Overall, ∼33% of the clones detected polymorphic loci. As expected, the highest level of polymorphism was found in interspecific hybrids (∼50%); whereas in intraspecific populations, only 1 in 5 genomic clones, and 1 in 3 cDNA clones were able to detect polymorphisms (RFLPs). These clones, as well as RAPD primers, are being used to construct a genetic linkage map by analyzing their segregation in 3 intraspecific peach populations (an Fl from France and two F2s from the U.S.). Taken together, these populations are segregating for 12 Mendelian traits and a number of quantitative traits. Our results have enabled us to identify a number of linkage groups, some composed of both molecular and phenotypic markers. The current structure of the peach map is reported.

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Peach [Prunus persica (L.) Batsch.] is considered the best genetically characterized species of the genus Prunus. We therefore used it as a model in our study of the genome organization in Prunus by means of restriction fragment length polymorphisms (RPLPs). Initial results indicated that 60% of cloned DNA sequences examined occur at low copy number within the peach genome. After selecting and examining these sequences, polymorphisms sufficient for RPLP mapping were found. We determined that ≫33% of our cDNA clones and 20% of our genomic clones detected RPLPs among peach cultivars. Analysis of RPLP segregation in two families, both of which segregate for known morphological characters, revealed segregation in 12 RFLP markers for one family and 16 for the other. Although we have not detected linkage between RFLP and morphological markers, preliminary analyses indicate possible linkage between two RPLP markers.

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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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