Mapping QTLs for Nut and Kernel Traits in Almond

Almond breeding is increasingly taking into account kernel quality as a breeding objective. Information on the parameters to be considered in evaluating almond quality has been recently compiled, including nut and kernel physical parameters, such as width, thickness, size, geometric diameter, spherical index, etc., as well as chemical components, such as protein, oil content, fatty acid and tocopherol concentration. The genetic control of these traits has not yet been determined in almond, although this information would improve the efficiency of almond breeding programs. With this aim a map with 56 SSR markers was constructed for an almond population showing a wide range of variability for the chemical components and for the nut and kernel physical parameters in almond. A total of 26 putative quantitative trait loci (QTL) controlling these chemical and physical traits have been detected in this analysis, corresponding to seven genomic regions of the eight almond linkage groups (LG). Some QTLs were clustered in the same region or shared the same molecular markers, as supported by the correlations between the traits. The logarithm of the odds (LOD) values for any given trait ranged from 2.12 to 5.17, explaining from 11 to 44% of the phenotypic variance of the trait. These results offer the opportunity to take into account new genetic information in almond breeding programs. Increases in the positive traits of kernel quality and nut/kernel physical traits may be pursued simultaneously whenever they are genetically independent, even if they are negatively correlated. The chemical components of the almond kernel have been placed in a preliminary genetic framework with twelve QTLs, in agreement with the large number of genes controlling their metabolism.