Fungal endophytes are known to confer enhanced tolerance towards both biotic and abiotic stresses to their host plants. Recently, bioactive secondary metabolites produced by these fungi have come into focus for potential application in agriculture. In particular, fungal volatile organic compounds (VOC) have shown application as fumigants to control fungal pathogens and insect pests of stored grain. These fungal VOCs open up new avenues to overcome resistance of stored grain pests to the widely used fumigant phosphine.
Using Solid-Phase Microextraction Gas Chromatography – Mass Spectrometry, a number of potential biocidal VOCs were identified in the volatolome of native endophytic fungi – Muscodor sp. and Nodulisporium sp. We evaluated these compounds in isolation and combination for their biocidal activity against major insect pests of stored grains such as Tribolium castaneum, Cryptolestes ferrugineus and Rhyzopertha dominica, and fungal pathogens such as Fusarium verticillioides. From the compounds tested, isoprene, produced by Nodulisporium sp, emerged as the most promising candidate as a stored grain fumigant. Small scale, mock grain silo experiments demonstrated good efficacy and low residue levels. Combining isoprene with other fungal VOCs further increased insecticidal activity, including at reduced rates.
Isoprene is highly volatile and produced commercially in large quantities as a building block for organic synthesis of rubber. It is naturally produced by many plant species, and is commonly found in low levels in many foodstuffs. It is the most abundant hydrocarbon detectable in human breath and has no acute toxicity, demonstrating its relative safety compared to other fumigants, including phosphine.