Mapping of a major gene for the slow ripening character in peach: co-location with the maturity date gene and development of a candidate gene-based diagnostic marker for its selection

Progeny of certain peach crosses include plants with slow ripening (SR) fruits that do not mature and remain on the tree after leaf fall. This character is determined by a single gene (Sr/sr) that segregated in the F-1 population of the cross between 'Belbinette' and 'Nectalady' (Bb x Nl). Heterozygous (Srsr) in both parents, the recessive srsr homozygote resulted in SR individuals. This gene mapped to linkage group 4 in a map constructed with SSRs in BbxNl, at the same genomic region previously found to contain a gene for maturity date (MD). An allele of a SCAR marker (PSR2) developed from the candidate gene for MD (ppa008301m), and with high sequence similarity to NAC transcription factors, was diagnostic for the sr allele in the Bb x Nl progeny, a collection of 135 normally-ripening cultivars and breeding lines, and 467 offspring of different lines segregating for this character. We developed an SSR marker, CPP15636, at this location (39 kb from PSR2), which had one allele associated with the character although a few recombinant individuals were identified. Both PSR2 and CPP15636 can be used for early identification and selection of normally-ripening genotypes in breeding programs. Data of MD in the population studied indicates that sr could be an allele of the MD gene. Given that the MD locus is partly responsible for the variability of the maturity date, we suggest that the sr allele in heterozygosis could confer desirable properties of postharvest behavior or specific maturity dates and would be preferentially selected in peach breeding.