Natural occurrence of Beauveria caledonica, pathogenicity to Cosmopolites sordidus and antifungal activity against Fusarium oxysporum f. sp. cubense

BACKGROUND Entomopathogenic fungi can provide a set of ecological services, such as suppressing arthropod pests and plant pathogens. In this study, novel indigenous Beauveria caledonica (Bc) strains were isolated from naturally infected banana weevils (Cosmopolites sordidus) occurring in commercial banana plantations in Brazil. RESULTS The prevalence of infection by Bc strains on field-caught C. sordidus ranged from 1.3% to 12.9%. Similar to the Beauveria bassiana strains tested, none of the Bc strains caused more than 50% weevil mortality at a concentration of 1 × 108 conidia ml−1. Bc strain CMAA1810 caused the highest mortality in C. sordidus and had enhanced insecticidal activity when formulated with an emulsifiable oil. In paired co-culture assays, this same strain showed a significant growth-inhibitory effect on the causal agent of Fusarium banana wilt (Fusarium oxysporum f. sp. cubense, Foc) of twofold magnitude compared with the control. Cell-free crude filtrates derived from the red-pigmented culture broth of Bc (CMAA1810) strongly reduced Foc conidial viability, and this inhibitory activity was inversely related to the age of the Bc culture. Crude concentrated filtrates from 4-day-old cultures exhibited the strongest antifungal activity (13-fold) compared with untreated Foc conidia. The abundant compound identified in the crude filtrate of Bc was oosporein (1,4-dibenzoquinone) present at a concentration of 0.829 ± 0.018 mg g−1 dry matter, and the antifungal activity of the filtrate was demonstrated. CONCLUSION These results indicated that Bc strains might have the potential to manage both C. sordidus and Foc, two of the major phytosanitary problems in banana crops worldwide. Further research under field conditions using suitable formulations of virulent Bc strains in combination with the metabolite oosporein is needed to evaluate their efficacy in the management of C. sordidus and Foc in banana plantations.