Phenotypic and molecular variability and genetic structure of Iranian almond cultivars

In this study, we used 20 morphological traits (during two consecutive growing seasons) and 11 microsatellite markers to assess the morphological and molecular variability and structure of the almond (Prunus dulcis (Mill.) D.A. Webb). Seventy one promising Iranian genotypes and three foreign reference cultivars (Ferragnes, Supernova, and Touno) were evaluated in this study. Kernel/shell ratio, kernel width/thickness ratio, softness of shell, nut weight, and kernel thickness were highly variable. Strong positive and, occasionally, negative correlations were detected among nut and kernel traits. Morphological traits were categorized by principle-components analysis (PCA) into 6 components which explained 88.1 % of the total variation. On the basis of the first two PCA axes, the 2-dimensional PCA plot grouped the samples according to their phenotypic characteristics. The results from molecular analyses (including a Bayesian clustering approach and a molecular phylogenetic network) did not correspond to morphological groupings. In this paper we report, for the first time, morphological and molecular variability and genetic structure of Iranian almond germplasm. Our results showed that model-based cluster analysis (using Structure software) was very appropriate for study of genetic relationships among almond accessions and can be used for study of the genetic structure of Prunus germplasm as well.