Persistence of Beauveria bassiana (Bals.) Vuill. on the ground over time

Abstract

The viability of B. bassiana evaluated through time (3, 8, 41, 95, 148, 218 days) in artifi­cially contaminated soil with 1 mi (10⁸ con/ ml), previously sterilized (SS) or not steril­ized (NSS) was investigated under labora­tory conditions. The soil was stored in Petri dishes at 25 ± 2°C. In order to evaluate the effect of soil type on the fungus, the Colony Forming Units (CFU) was recovered on SDA and on a selective medium (SM) using the soil dilution píate method. The mean num­ber of viable conidia was calculated and then converted to CFU per g of dried soil. On the SM the fungus was recovered at 148 d (9.5 ± 4.0 x 1W CFU/g) and at 218 d (1.7 ± 1.8 x 10³ CFU/g) in NSS. In SS at 148 d, 9.8 ± 2.1 x 10³ CFU/g and at 218 d, 9.0 ±6.0 x 10² CFU/g of B. bassiana were recovered. The fungus was not recovered on SDA. During the assay, the mean number of viable conidia declined through time. However, an unexpected temporary in-crease in the number of CFU was observed at 41 d (1.67 x 10⁵ CFU/g in SS on SDA and 8.9 x 10⁵ CFU/g in SS on SM) and at 8 d (7.0 x 10⁴ CFU/g in NSS on SDA and 3.0 x 10⁴ CFU/ g in NSS on SM). The reasons for this increase are yet unknown.