Construction of a linkage map and QTL analysis of agronomic traits in almond using SSR markers

Developing new cultivars is a long and tedious process in temperate fruit crops such as almond [Prunus dulcis (Miller) D.A. Webb], involving the generation of a huge seedling population from which the best genotypes will be selected. While the ability of breeders to generate large populations is almost unlimited, the management, study and selection of these seedlings are the main limiting factors in the generation of new cultivars. The identification of molecular markers associated with agronomic traits is of great interest for the Prunus breeding programs, and could accelerate enormously the selection process. In this study five tree traits (blooming time, leafing time, self-compatibility, productivity and ripening time) and three pomological traits (shell hardness, double kernel, and kernel bitterness) were studied in an almond progeny of 167 seedlings from the French cultivar "R1000" and the Spanish cultivar "Desmayo Largueta". On the other hand, a set of 56 codominant SSR (simple-sequence repeat) markers developed from peach, cherry and almond were used for the molecular characterization of the progeny. A genetic linkage map was constructed with these 56 SSR markers and QTL (quantitative trait loci) analysis was performed in order to establish linkage between SSR markers and the agronomic traits. The development of efficient marker-assisted selection (MAS) strategies applied to almond and other Prunus breeding programs are discussed.