Population Structure And Character Of Mutant Isolate In Cryphonectria Parasitica

Chestnut blight epidemic is associated with devastation ofCastanea, Chestnut blight also one of an important disease in the forests. The population diversity of Cryphonectria parasitica was studied in this thesis.One hundred and fourteen isolates of C. parasitica collected from 11 provinces in the east of China were tested for their mating type with four standard tested isolates. Results showed that both mating types, MAT-1 and MAT-2, exist in C. parasitica population of China. MAT-1 partial mating-type idiomorph of C. parasitica isolates 133 and 293 were cloned and sequenced. Analysis of partial sequences of MAT-1 idiomorph of C. parasitica isolates 133 and 293, found the sequence of partial idiomorphs are 94% and 97% identical to the partial sequence from GeneBank. A PCR assay was carried out to determine the mating-type of C. parasitica isolates obtained from eastern China, it was found that MAT-1 and MAT-2 was 50% in the 266 isolates from eastern China. In most of isolates from the same location the tested locations, two mating types existed together. Ascospore progeny strains from the fungal perithecia segregated for mating type at ratio of 1:1. The test results of mating type to 87 of 114 isolates by PCR and crossing in pair to standand isolates were consistant, but the other 26 of 114 isolates were different suggestting that the sexual stage occurred in natural condition, the sexual recombination might be a potential resource for the genetic diversity of C. parasitica.The population structure of C. parasitica was analyzed using random amplified polymorphic DNA (RAPD). 23 isolates of each of eight perithecia and the fungal asexual populations as the samples collected from natural garden, and assayed for genetic diversity by using 4 RAPD primers with abundant polymorphisms. 73 RAPD mark bands were obtained and 100% of them were polymorphic. Ascospore strains from peritheria showed much more variability among themself, in contrast with field asexual isolates showing lower genetic diversity. Genetic diversity and UPGMA dendrogram were analyzed by use of Popgen Version 1.31,and the results showed that the genetic variation between perithecia were rich: 64.27% was attributed to diversity within populations, as compared with 35.73% among populations. Gene flow value (Nm) was 0.8994 between different peritheria while the genetic distance among sexual and asexual populations was 0.1389, but the gene flow estimate was 3.4212...