THE USE OF MOLECULAR GENETICS TO IMPROVE PEACH AND NECTARINE POST-STORAGE QUALITY

Abstract

Internal breakdown (IB), also known as chilling injury, is the collective term for various disorders that occur during prolonged cold storage and/or after subsequent ripening of stone fruit. Symptoms include mealiness, flesh browning, loss of flavor, and red pigmentation (bleeding). Some cultivars tend to be more susceptible than others and heritability estimates are moderate, indicating that the symptoms have a significant genetic component. However, the genetic mechanisms by which low susceptibility genotypes avoid IB symptoms are not clear. Using two related and genetically variable populations of peach, we have undertaken a classical and molecular genetics approach to gain a better understanding of the genetic control of IB and lay the foundation for marker-assisted selection (MAS) for these traits. A partial genetic linkage map was constructed, based on SSR (simple sequence repeat) and RAF (randomly amplified polymorphic DNA) markers, candidate gene markers, morphological markers, and gene-targeted SRAP (sequence-related amplified polymorphism) markers. QTL analysis was performed on the linkage groups, using phenotypic data collected for two seasons. QTLs for flesh mealiness, browning, and bleeding were located. Candidate gene analysis identified that a gene encoding the cell wall degrading enzyme, endopolygalacturonase, co-segregates with the freestone and melting flesh traits. A large QTL for mealiness was detected for this locus, reflecting the observation that mealiness occurred only in freestone melting flesh progeny and was entirely absent in clingstone non-melting flesh progeny. The use of MAS in breeding for low susceptibility to internal breakdown symptoms in peach appears to be an achievable goal.