环链棒束孢菌株培养特征、致病性及遗传变异研究

为筛选一种对小菜蛾有高致病力的杀虫真菌，对来自不同地域的环链棒束孢菌株的培养特征尤其是孢梗束形成、对小菜蛾的致病性和基于5.8S-ITS nrDNA构建的系统发育等进行分析。结果表明，供试菌株的培养性状可分为3个类型：孢梗束浓密型、孢梗束稀疏型和不产孢梗束型。孢梗束浓密型对小菜蛾的致病性最高，平均达到88.9%，其中XS.1菌株，对小菜蛾幼虫的致死率达到98%；孢梗束稀疏型次之，为68.4%；不产孢梗束型最差，仅35%。系统发育聚类树分析表明，在环链棒束孢菌株中，致病性较高的菌株，如XS.1，XS.2和SL.7等聚在一亚分支内，致病性低的菌株8.02和468.10聚在一起；不产孢梗束的两个菌株8.02和468.10聚在一个亚支。这些结果表明环链棒束孢菌株间具有明显的种内遗传变异性。孢梗束形成与小菜蛾的致病死亡率有相关性。孢梗束的形成可作为高致病性菌株选择的一个重要指标。

Culture characteristics, pathogenicity, and genetic variation of Isaria cateniannulata isolates

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.