Genetic diversity and gene flow of some Persian walnut populations in southeast of Iran revealed by SSR markers

Iran is reported to be a center of diversity for Juglans regia and wild walnut trees are found in virtually every corner of the country. Thus Iran is considered a rich natural pool of walnut germplasm for developing improved genotypes. Kerman province is the most important Iranian province for walnut culture and has the largest walnut plantations in Iran. Genetic structure and gene flow were analyzed in six walnut populations of this province using 17 microsatellite loci. The number of alleles per locus ranged from 4 to 11, with a total of 147 alleles and 5.16 effective alleles per locus. The polymorphism information content for the loci ranged from 0.56 to 0.82. The expected heterozygosity (He) for the populations ranged from 0.65 to 0.87. There were differences between populations regarding the number of effective alleles and Shannon’s information index (I). In all populations, observed heterozygosity (Ho) was lower than expected, but diversity within the populations was high (I = 1.5) and many of the private alleles were present at relatively high frequency. The average Fst value was 0.08. The level of gene flow based on Fst was high (Nm = 3.01), which meant that the high level of genetic diversity maintained within each population was less susceptible to genetic drift. The geographical proximity of the populations was not correlated with their level of genetic relatedness. These results imply the high potential of walnut populations of Kerman province for breeding programs.