Metarhizium anisopliae reduces conidial germination and mycelium growth of the apple gray mold Botrytis cinerea

Fresh apple market is affected every year by losses caused by fungi invasion and spoilage, with Botrytis cinerea one of the main responsible pathogens. The objective of this study was the characterization of the in vitro antagonistic activity of Metarhizium anisopliae Ma70 against Botrytis cinerea and its trial on apple fruit. The antagonism was tested by dual cultures, cellophane membrane assay and the effect of M. anisopliae crude extract over conidia germination and mycelium growth of B. cinerea. The trials on apple fruit evaluated crude and semi purified extracts activity against apple gray mold. Antifungal volatile organic compounds produced during the process were determined using GC-MS. We observed that M. anisopliae (Ma70), reduced the B. cinerea growth by 60-63% (P < 0.01). Pathogen's mycelium is degraded, even without physical contact. Cellophane tests showed that growth inhibition by antibiosis reach a 88%. The Ma70 extracts affects conidia germination (92%) and mycelial growth (50-80%) of B. cinerea. The phytopathogen suffers membrane lipoperoxidation by the effect of antagonist extracts, the malondialdehyde production was increased by a factor of two, in mycelium and in the culture medium. We observed that crude (CE) and semi-purified (SPE) MA70 extracts reduced the damage caused by B. cinerea in apple. The B. cinerea growth inhibition by the VOCs produced by Ma70 was different depending on the culture media, with the highest inhibition effect (75%) seen in sabouraud dextrose agar plus yeast extract. Twenty-eight volatile organic compounds (VOCs) were identified in CE (mainly oxalic acid) and 13 in SPE (mainly octane,1-methoxy). Only 1-Octanol appears in both CE and SPE. M. anisopliae Ma70 can be an effective treatment for biocontrol of the apple gray mold disease, producing compounds that inhibited conidia germination and mycelium growth of B. cinerea.