| The population diversity of chestnut blight fungus, Cryphonectria parasitica and its double strand RNA were studied in this thesis.dsRNA virus of Cryphonectria parasitica was studied by use of biological assay and gel electrophoresis. dsRNA viruses of C. parasitica from east of China were divided into 4 types on the basis of electrophoresis patterns. Type 1 has only one segment of 12.7kb, accounting for majority of the total isolates. Type 2 has another large segment about 10kb besides the segment of 12.7kb, containing 4 isolates. Type 3 has 2 or 3 small segments shorter than 2kb other than the segment of 12.7kb, containing 3 isolates. Only 1 isolate belonged to type 4, it has 2 small dsRNA segments about l~2kb. The cultural character of all these tested isolates were various and divided into 5 cultural types. Cultural type of C. parasitica is not consistent with the type of dsRNA. Virulence test results showed there was certain difference betweenthe isolates containing dsRNA.A total of 113 isolates of C. parasitica from 7 populations, viz. Jiangsu, Beijing, Liaoning, Fujian, Italy, Japan and America, were amplified with 9 RAPD primers which were selected from 120 ramdom primers. 124 RAPD fragments were obtained and 89.52% of them were polymorphic. Genetic diversity and UPGMA dendrogramwere analysed by use of Popgen3.2. The results showed that 4 populations in China were more similar to each other, than to populations in Italy and America; America and Italian populations were similar to each other, and more similar to Japanese than to Chinese. Gene diversity was decomposed hierarchically. At region level, the gene diversity of the total population was 0.2351, 82.34% of gene diversity was attributedto diversity within populations, compared to 17.66% among populations, the gene flow estimate among populations was 2.3311. While at host level, the gene flow value was 1.9297, with 79.42% of gene diversty attributable to diversity within populations and 20.58% among populations.
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