Genetic diversity of the Spanish Pear Germplasm Collection assessed by SSRs

The Spanish Pear Germplasm Collection located at the CITA (Centro de Investigación y Tecnología Agroalimentaria de Aragón, Zaragoza, Spain), holds 340 accessions of Pyrus communis and 9 accessions of Pyrus pyrifolia. It includes commercial and traditional cultivars, and also Spanish sources. This collection has already been morphologically characterized, and 170 accessions have now been genotyped with 17 SSRs. This study aims to determine the genetic identity of the pear collection, to assess the genetic diversity and relationships among those accessions and to elucidate its genetics in the studied germplasm. With the exception of GD96, all primer pairs produced a successful amplification, varying the number of alleles from six (locus CH05a02) to 21 (locus CH04c07) averaging 13.76 alleles per locus, giving a total of 234 fragments and 743 different genotypes. Allele size ranged from 85 bp at locus CH05C06 to 300 bp at locus CH01D08. The expected mean and observed heterozygosity over the 17 SSRs averaged 0.77 and 0.69, respectively. Three Spanish cultivars, ‘Duquesa Barreda’, ‘Limón de Verano’ and ‘Limón Antiguo’, showed heterozygosity in all analysed loci. On the other hand, genotypes showing heterozygosity lower than 0.45, were the P. pyrifolia cultivars ‘Nijisseiki’, ‘Seigyoku’, ‘Shinseiki’, and the Spanish ‘F de los Bosques’. UPGMA (unweighted pair group method analysis) was performed in order to determine the genetic uniqueness of each accession and to know the genetic relationships among the studied accessions. It classifies genotypes according to their geographical origin, confirming the particular evolution of different pear ecotypes. Structure analysis showed a strong subpopulation structure, where the accession origin and Pyrus species were important factors of grouping. Therefore, SSRs appear to be excellent markers to provide genetic information and a viable approach for carrying out genetic diversity studies as well as to identify the majority of the cultivars.