Characterisation of in vitro cultured strains of Beauveria bassiana and Metarhizium anisopliae through poison food technique to evaluate their pesticide tolerance and genetic variability

Abstract

Entomopathogenic fungi have high potential for efficient suppression of a variety of arthropod pests. However, their field application is easily affected by the potential inhibitory effects of various pesticides. The compatibility of two fungicides and 6 insecticides with Beauveria bassiana (Balsamo) Vuillemin and Metarhizium anisopliae (Metschnikoff) Sorokin was determined under laboratory conditions, adopting the poison food technique. The growth, sporulation and bioefficacy of the fungi grown on the poison food media were assessed. In order to develop pesticide-tolerant strains, both fungi were grown separately in poisoned media continuously for 10 passages with an increase in concentrations of pesticides. The DNA isolated from the fungal cultures was subjected to DNA fingerprinting and PCR amplification reactions using 10 primers. A genetic similarity matrix was constructed using Jaccard’s similarity coefficient values and this matrix was subjected to an unweighted pair-group method for arithmetic average analysis (UPGMA) to generate a dendrogram using the average linkage procedure to assess variability induced by pesticide exposure. The results showed that although growth was inhibited, both fungi survived in all pesticide-amended media. Beauveria bassiana recorded the maximum radial growth (9 cm) in 13 days, followed by the cultures grown in imidacloprid, carbosulfan, carbofuran and chlorpyriphos and showed statistical significance from the other treatments. Polymorphism was higher for B. bassiana cultured in carbendazim. The polymorphism exhibited in B. bassiana was higher (83.19 %) compared to M. anisopliae (38.46 %).  Among the 10 universal fungal primers evaluated, RFu-10 was found to give maximum polymorphism.