Exploring almond genetic variability useful for peach improvement: mapping major genes and QTLs in two interspecific almond × peach populations

Genetic analysis of a diverse set of 42 traits for flower (5), phenology (9), fruit quality (19), leaf (8) and disease resistance (1) was carried out in two interspecific almond × peach populations, an F₂ (T × E) and a BC₁ (T1E), from the cross between ‘Texas’ almond and ‘Earlygold’ peach. Traits related to flower, phenology, fruit quality, leaf morphology and resistance to powdery mildew were phenotyped over 3 years in two locations and studied for co-segregation with a large set of SNP and SSR markers. Three maps were used, one for the T × E and two for the T1E (T1E and E) population. Nine major genes were identified and mapped: anther color (Ag/ag and Ag2/ag2), flower color (Fc2/fc2), maturity date (MD/md), almond fruit type (almond vs. peach; Alf/alf), juiciness (Jui/jui), blood flesh (DBF2/dbf2), powdery mildew resistance (Vr3) and flower type (showy/non-showy; Sh/sh). These genes were often located in genome positions different from those for major genes for similar traits mapped before. Two of them explain fundamental aspects that define the fruit of peach with respect to that of almond: Alf and Jui, for its thick and juicy mesocarp, respectively. The genetics of quantitative traits was studied, and 32 QTLs were detected, with consistent behavior over the years. New alleles identified from almond for important traits such as red skin color, blood flesh, fruit weight and powdery mildew resistance may prove useful for the introduction of new variability into the peach gene pool used in commercial breeding programs.