Culture characteristics, pathogenicity, and genetic variation of Isaria cateniannulata isolates
环链棒束孢菌株培养特征、致病性及遗传变异研究

To develop a simple and feasible way to screen high virulent fungal pathogen against insect, culture characteristics, especially the phenotypes of synnema formation, pathogenicity against Plutella xylostella larvae, and genetic variation of 5.8S-ITS rDNA sequences were evaluated for the Isaria cateniannulata isolates collected from different geographical regions. Culture characteristics of the isolates tested displayed three different types, dense synnema, loose synnema and no synnema. The type with dense synnema had high pathogenicity with over 88.9% of larva mortality rate. The highest mortality rate of the insect (98%) was caused by the isolate XS.1 in this type. The next best was the type with loose synnema, which resulted in a 68.4% of the mortality. Only 35% of larva mortality was caused by the isolates in the type without synnema suggesting a low pathogenicity. Phylogenetic analysis showed that the strains with high pathogenicity such as XS.1, XS.2 and SL.7 were closely clustered to a subclade and the strains with lower pathogenicity including 8.02 and 468.10 were clustered together. Isolates 468.10 and 8.02 without synnemata were clustered in a separated subclade. These results demonstrated a distinct intraspecific genetic variation, and a relevance of the ability to produce synnemata to the virulence against P. xylostella larvae in I. cateniannulata. Thus, the ability of synnema formation could be an important factor to screen high virulence isolate of I. cateniannulata isolates.