Spores production of Beauveria bassiana y Metarhizium anisopliae isolates in different sustrates

Abstract

This study quantified the spore production of 12 "isolates M. anisopliae and 10 of B. bassiana, obtained from the orders Coleoptera, Homoptera, Lepidoptera and Orthoptera, these isolates are known to cau­se pathogenicity levels greater or equal to 80 % in the coffee berry borer. They were cultivated on a rice substrate and coffee berry borers. For the rice substrate cultivation, two bottles per isolate were used, each of them containing 50 grams of rice. The bottles were incubated for 30 days, after which five sporulated rice samples per bottle were taken. The spore count was made from these by using successive dilutions of the original sample. With regard to the coffee berry borer substrate, 30 individuals per isolate were inoculated and these were incubated in a humid chamber for a 10 day period and afterward, each fungus colonized in the borer was transferred to a test tube containing 4,5 mkof distilled water, for counting purposes. In the rice substrate, isolates Bb9207, Bb 9301, Ma 9236 presented the greatest number of spores: respectively, 3.57 x 10¹°, 1. 53 x 10¹⁰, 1.31 x 10¹⁰ spores/gram. These were statistically different from the rest of isolates; the isolate with the least number of spores was Ma 9303 with 1.65 x 10⁸ spores/gram. In the coffee berry borer substrate, isolate Bb 9218 presented the greatest sporulation with a total of 1.36 x 10' spores/borer, those with the lowest sporulation were eight of M. anisopliae and one of B. bassiana with an average of 5.86 x 10⁵ spores/borer. At the same time, pathogenicity and sporulation were observed as independent characteristics. These results demonstrate that spores production depends on the isolation and interaction with the culture media in which develops.