Identification and Genetic Relationship of Persian Walnut Genotypes Using Isozyme Markers

Abstract

Horizontal starch gel electrophoresis was used to identify 108 walnut genotypes and to assess their genetic relationship. The DIA, 6-PGD, PGM, SDH, MDH and MPI enzyme systems were encoded for 12 loci, 8 of which were polymorphic. With just three systems (DIA, 6-PGD, PGM), nearly 70% of the studied genotypes were identified. Four systems (DIA, 6-PGD, PGM, SDH) allowed for more than 80% to be identified and all 6 systems studied made it possible to distinguish over 90%. Eight loci were found to be more than sufficient to identify 91 of the 108 genotypes studied.

The Nei and Li index suggests that walnut germplasm is very closely related, with an average value among all genotypes of 0.775. Cultivars from Romania ('Oprean', 'Maria Mamma' and 'Sibisel-39') showed markedly lower similarity indices than the other cultivars.

The UPGMA dendrogram based on the similarity matrix separated the walnut genotypes included in this study into two clear groups. The first group consisted of two sub-clusters, one of which mainly comprised genotypes from Spanish, French, Chilean and other European cultivars. The other sub-cluster consisted primarily of Californian cultivars closely related to the 'Payne' cultivar. The second main group, though much smaller in size, mainly comprised genotypes from Iran and Romania. Isozyme markers have proven to be useful tools for identifying and fingerprinting walnut cultivars.