Application of a Standardized Protocol for Fruit Quality Phenotyping in the Arkansas Peach and Nectarine Breeding Program

Molecular techniques are becoming more commonly utilized in peach [Prunus persica (L.) Batsch] breeding programs for several purposes: to screen genotypes as juveniles before they produce fruit; to discard individuals that do not carry certain desired alleles; and to select parents for crossing based on specific alleles. Ultimately, this application will increase breeding efficiency and reduce operational costs, labor, and land. These new techniques are precise and when correctly applied can lead to accurate and useful results, but they only work if accurate and standardized phenotyping procedures are used over multiple years. Within the Arkansas peach breeding program a wide and unique range of flesh types are found, including melting-flesh (MF), non-melting flesh (NMF), non-softening flesh (NSF), and slow-melting flesh (SMF). These flesh types have different textures, firmness, and postharvest performance potential. As a part of the RosBREED project (www.rosbreed.org) the University of Arkansas peach breeding program has applied a standardized phenotyping protocol for fruit quality on seven peach populations and their parents since 2010 to relate genotypic and phenotypic data. This protocol involves qualitative and quantitative trait characterization, such as: fruit and pit mass, fruit diameter, flesh firmness, flesh texture, flesh adherence to the pit, skin and flesh color, soluble solids content, titratable acidity, pH, bloom date, and ripening date. Along with phenotyping, endopolygalacturonase (endoPG) genotyping for flesh type differentiation was conducted on these genotypes in 2011. Phenotyping of fruit quality traits was conducted at the well-mature stage. Within these seven populations, the MF, NMF, and SMF textures were phenotypically distinguishable and matched the expected flesh firmness values. The MF individuals, which were expected to have the lowest firmness, had an average value of 1.9 Kg of force (Kgf), the SMF individuals (which have a reduced rate of melting phase) averaged 2.7 Kgf, and the NMF individuals averaged 3.3 Kgf. Endopolygalacturonase DNA markers were able to differentiate between MF, NMF, and NSF individuals but were unsuccessful in identifying SMF individuals. These findings facilitate further research in developing a more accurate characterization of the peach flesh types.