Genetic Diversity of New Almond Accessions from Central Asian and Cold-adapted North American Germplasm

We evaluated the genetic diversity of a newly available collection of 94 almond [ Prunus dulcis (Mill.) D.A. Webb] accessions from the former Improving Perennial Plants for Food and Bioenergy (IPPFBE) Foundation. Most of the collection (87 accessions) were collected as seeds from trees growing in the central Asian nations of Kyrgyzstan, Tajikistan, and Uzbekistan, and included several examples of Prunus bucharica (Korsh.) Hand.-Mazz, and related wild species. Of the remaining accessions, six were sourced from a nursery in northern Utah in the United States, and one was a seedling of ‘Nonpareil’, a major commercial cultivar. DNA fingerprints were generated from 10 simple sequence repeat markers. To evaluate the comparative diversity of these new accessions, 66 accessions from the US Department of Agriculture, National Plant Germplasm System (NPGS) almond germplasm collection near Davis, CA, USA, were also included. These NPGS accessions were chosen to represent those collected in similar regions of Central Asia and the Caucasus. The fingerprints were analyzed via hierarchical clustering, principal components analysis (PCA), and discriminant analysis of principal components (DAPC). Hierarchical clustering suggested that half of the Utah-sourced accessions are closely related to each other and to the ‘Nonpareil’ seedling. Additional close relationships were detected (including at least one duplication or mislabeling), and two P. bucharica accessions from the IPPFBE collection were separated from the rest of the collection. A plot of the first two principal components clearly separated wild almond relatives ( P. bucharica and Prunus fenzliana Fritsch) from the remaining accessions. PCA after removal of the wild species separated the ‘Nonpareil’ seedling, the Utah-sourced accessions, and many of the IPPFBE accessions (mostly from Uzbekistan) from nearly all other individuals. The third principal component identified an additional population structure that separated groups of predominantly IPPFBE or NPGS accessions. DAPC showed a considerable admixture of accessions from Azerbaijan, and a little to no admixture of accessions from Georgia and Tajikistan. These results suggest that central Asian/Caucasian almond germplasm is generally distinct from ‘Nonpareil’ and its relatives, and that although there is overlap between the NPGS and IPPFBE collections from this region, the IPPFBE collection does enhance the diversity of available almond germplasm.