EFFECT OF SYNTHETIC PESTICIDES ON CONIDIAL GERMINATION AND ENDOPHYTIC ACTIVITY OF Beauveria bassiana AND Metarhizium anisopliae IN COMMON BEAN PLANTS

Abstract

Common bean (Phaseolus vulgaris L.) is an important legume crop worldwide. Endophytic fungi have proven effective as biocontrol agents in several crops, but they can be affected by pesticides. The aim of this study was to evaluate the effect of synthetic pesticides on the conidial germination and endophytic activity of Beauveria bassiana and Metarhizium anisopliae in P. vulgaris. Three fungicides (Mancozeb, Tebuconazole and Zinc Ethylene-bis), three insecticides (Abamectin, Diazinon and Spirotetramat) and one herbicide (Glufosinate) were evaluated. Each pesticide was applied at the application rate recommended by the manufacturer and also using one-half of the application rate on the commercial strains B. bassiana Bb-18 and M. anisopliae Ma-30. Tebuconazole, Mancozeb and Glufosinate totally inhibited conidial germination. Spirotetramat and Diazinon resulted in a less pronounced negative effect on B. bassiana and M. anisopliae germination. However, Spirotetramat has the lowest impact on the entomopathogenic fungi, allowing for 86 and 74% germination of B. bassiana and M. anisopliae, respectively. Tebuconazole and Mancozeb affected the endophytic activity of the entomopathogenic fungi studied. At one-half of the recommended concentration, Spirotetramat and Zinc Ethylene-bis allowed for the total colonization of B. bassiana in roots of common bean, whereas M. anisopliae reached a colonization of 75%. These results indicate that Spirotetramat, Zinc Ethylene-bis and Diazinon can be used in combination with B. bassiana Ba-18 and M. anisopliae Ma-30. However, Tebuconazole, Mancozeb and Glufosinate should not be combined with these entomopathogenic fungi in Integrated Pest Management programs.