Identification of whitefly pathogenic fungal strain IfB01 and optimizaton of sporulation conditions

Objective To identify the taxonomic of IfB01 strain, which was isolated from tobacco white-fly, and to optimize its sporulation conditions.

Method Identification of IfB01 strain was based on morphological analysis and genetic homology analysis of ITS1-5.8S-ITS2 rDNA sequence and β-tubulin DNA genes. The effects of culture medium, moisture content, pH, amount of inoculation and metallic element on conidial yield were studied. The sporulation conditions were optimized according to the above-mentioned effects.

Result and conclusion The morphological structure of IfB01 strain was similar to that of Isaria fumosorosea, including colony morphology, conidia and sporulation structure. Analysis of ITS1- 5.8S-ITS2 rDNA sequence and β-tubulin DNA sequences indicated that IfB01 strain shared similarity over 97% with Isaria fumosorosea and Paecilomyces javanica. The strain was identified as I. fumosorosea. Basic media and their ratios, moisture content, pH, inoculum dosages and metallic elements could generate significant influences on the conidiospore production. The sporulation quantity of each gram of corn flour and wheat bran mixed medium was 6.07 × 10⁹, which was the most suitable medium for sporulation. When the ratio of corn flour and wheat bran was 5:5, the moisture content of the medium was 42%, the inoculation amount was 6 mL bacteria liquid of each 20 g medium, the highest spore quantity was achieved. A wide range of pH from 5 to 8 could be adapted. However, metallic elements did not seem to promote sporulation, on the contrary, magnesium, iron, sodium and calcium could inhibit conidia production.