Assessment of germplasm diversity and genetic relationships among walnut (Juglans regia L.) genotypes through microsatellite markers

Jammu and Kashmir region of India has a rich walnut germplasm that has arisen from populations of naturally grown seedlings and some introductions from other countries over many years. In this study, the genetic relatedness of 96 walnut genotypes adapted to the North Western Himalayan region of Jammu and Kashmir, India, was analyzed by 19 SSR markers. Genetic relationships among 96 walnut genotypes revealed very high polymorphism rate of 89.6%. Primer parameter values viz PIC, MI and Rp range from 0 to 0.43, 0 to 0.87 and 1.04 to 2.37 with an average of 0.168, 0.244 and 1.91 respectively. UPMGA dendrogram showed that all the accessions formed twelve main clusters with various degree of sub-clustering within the clusters. Model-based cluster analysis grouped 96 walnut genotypes into 5 genetically distinct sub-populations with varied level of admixture. Allele Frequency Divergence and expected heterozygosity vary from 0.00 to 0.057 and 0.043 to 0.067 with an average of 0.024 and 0.057 respectively between all the five populations. These studies will be helpful in association mapping studies for important traits in walnut. The high variability existing in the walnut germplasm suggested that it would be beneficial to utilize this germplasm pool in walnut breeding programs and germplasm management activities and also identified microsatellite markers for cultivar identification, characterization, registration and assessment in genebanks. Keywords: Juglans regia, SSR markers, Molecular characterization, Structure analysis, Genetic diversit