Abstract：Genetic diversity and genetic differentiation of Cryphonectria parasitica，which were from China, Japan, Italy and the USA, were analyzed using inter simple sequence repeat (ISSR) molecular technique. Using 11 primers filtrated from total 53 primers, ISSR amplification was conducted in 220 individuals from eleven Cryphonectria parasitica subpopulations which were from four countries, and 174 polymorphic loci were detected from total 177 loci. The percentage of polymorphic loci (P) of the total populations was 98.31%, while that at a subpopulation level averaged 20.43 %. Shannon’s Information index (I) and Nei’s gene diversity (h) of the fungus at the total populations level was 0.1769 and 0.7386, respectively. The mean of I and h at a subpopulation level was 0.0943 and 0.0614, respectively. It indicated that the genetic diversity of C. parasitica between the populations was relatively high. The genetic differentiation coefficient (Gst) among populations was 0.7386. The gene flow (Nm) among populations was low down to 0.1769. The mean of pair-wise genetic distance between eleven C. parasitica subpopulations was 0.2289. These eleven subpopulations could be clustered into three groups using unweighted pair group method with arithmetic mean (UPGMA).
