Genetic diversity of Cryphonectria parasitica populations in Asia, Europe and North America
亚欧美栗疫病菌群体的遗传多样性

To study the population structure of the chestnut blight fungus Cryphonectria parasitica, a total of 142 isolates representing seven geological regions including China, Japan, Italy, and the United States were subject to random amplified polymorphic DNAs (RAPDs) analysis. Among the 120 random primers tested, nine were found to generate distinct DNA fragments. Our studies have shown that 89.52% of 124 RAPD fragments were polymorphic and the Jianyang population of China was the most polymorphic (66.94%), whereas the Japanese population was the least polymorphic (37.1%). When analyzed at the host level, gene diversity of total populations (H_T) was estimated at 0.1887. However, the gene diversity occurred mainly within populations (79.42%), not between populations (20.58%). The estimated average gene flow (N_m) between populations was 1.9297 and the ratio of polymorphic RAPD fragments obtained from the populations that have Castanea crenata as the host was the highest (72.58%). Additionally, the gene diversity (H) of the population isolated from C. henryi was highest at 0.2263, whereas the ratio of polymorphic RAPD fragments and gene diversity (H) of the population from C. sativa were among the lowest. Furthermore, the gene diversity of the total populations (H_T) was 0.2351 and that within populations (H_s) was 0.1936 at region level. 82.34% of gene diversity was attributable to the diversity within populations than between populations (17.66%, G_(st)=0.1766). Finally, the gene flow estimate between populations (N_m) was 2.3311, denoting that there was gene flow between populations. Our results conclude that the population gene diversities (H_T) are the greatest in China. The genetic similarities of RAPD frequencies among populations indicate that Chinese populations are similar to each other, but are distinct from populations of Japan, Italy, and the United States. Interestingly, there is less differentiation between Japanese and American populations and between Japanese and Italian populations than that between Japanese and Chinese populations despite the fact that Japan is geographically closer to China.