Thet Thet Mar, Nakarin Suwannarach and Saisamorn Lumyong
Microbiology Division, Department of Biology Faculty of Science, Chiang Mai University, Chiang Mai, 50200 Thailand.
Spore productivity in six entomopathogenic fungal strains isolated from insect cadavers at four locations in Chiang Mai province was evaluated in five cereal grains: white-rice, wheat, rye, corn and sorghum. According to sequence analysis of the internal transcribed spacer regions of these isolates, they were closely related to Beauveria bassiana (2 isolates), Metarhizium flavoviride (1 isolate), Metarhizium anisopliae (1 isolate), Paecilomyces lilacinus (1 isolate) and Isaria tenuipes (1 isolate). Among all fungal isolates, the maximum amount of spores (530.0 × 109 conidia/g) was yielded P. lilacinus CMUCDMT02 on sorghum grain followed by white-rice (399.3 × 109 conidia/g). Moreover, the highest number of spore in M. flavoviride was 102.8 × 109 conidia/g sorghum whereas white-rice yielded the greatest amount of spore for B. bassiana CMUCDMF03 (141.0 × 109 conidia/g) after 60 days incubation. The fungal growth rate was found highest in corn for all strains and rye showed the lowest with the exception of P. lilacinus CMUCDMT02 among the tested grains. Spore viability was over 80 % for all isolates that had been inoculated for 60 days. Fungal conidia suspension of P. lilacinus obtained highest virulence against Bactrocera spp. at a concentration of 1 × 106 spore/ml. The strains isolated, exhibited good production of conidia suggesting a promising strategy for the mass production of inoculum as biocontrol agents with low production cost.