RFLP markers were used to investigate genetic diversity among California walnut (Juglans regia) cultivars and germplasm collected worldwide. Sixteen of 21 RFLP markers were polymorphic in the 48 walnut accessions tested. RFLP markers were useful for identifying walnut cultivars. All genotypes were heterozygous at ≈20% of the loci for both California and worldwide germplasm. California walnut germplasm contained 60% of the worldwide allelic diversity. Cluster analysis of genetic distance between accessions and principal component analysis of allelic genotypes showed two major groups of walnut domestication. California germplasm was associated with germplasm from France, central Europe, and Iran and had less genotypic similarity with germplasm from Nepal, China, Korea, and Japan.
R.G. Fjellstrom, D.E. Parfitt and G.H. McGranahan
Dan E. Parfitt, M.L. Badenes and R.G. Fjellstrom
Chloroplast DNA polymorphisms were obtained using a combination of RFLP analysis of total cpDNA and a combination of PCR amplification restriction of a 3.2-kb region of cpDNA described previously. Nuclear genome analysis was conducted using 21 RFLP probes that revealed 192 alleles. Parsimony analysis of nuclear DNA places J. cinerea between J. regia and other Asian species, while Wagner-Distance analysis places all North American species between them. cpDNA parsimony also placed the North American species between J. regia and remaining Asian species, but did not resolve the placement of J. cinerea, because all North American species were monomorphic. Both analyses support an ancient origin for J. regia and multiple migration events between North America and Asia.