EFFECTS OF NEEM LEAF VOLATILES ON SUBMERGED CULTURES OF AFLATOXIGENICASPERGILLUS-PARASITICUS

Microbe-free compressed air was passed continuously for a S-day test p eriod through an enclosed system containing fresh neem leaves; the res ultant emitted volatiles were passed over the surface of submerged liq uid cultures of a wild-type aflatoxigenic isolate of Aspergillus paras iticus. Aflatoxin determinations for the fungal culture that received neem-derived volatiles, after a 3-day incubation period, resulted in a 90% overall reduction in aflatoxin production and a 51% reduction in fungal biomass when compared with cultures that did not receive neem v olatiles. In a separate experiment but in a similarly enclosed system, volatiles from fresh neem leaves were collected on a small Tenax colu mn and were thermally desorbed and cryogenically focused on a capillar y gas chromatography column. The neem volatiles-were subsequently sepa rated and identified by gas chromatography-mass spectrometry. Sixty-ei ght compounds were identified by comparison of retention times and mas s spectra with either authentic compounds or spectra from a computer-a ssisted library database of mass spectra. It was found that 10% of the total headspace volatiles were composed of C-3 to C-9 alkenals, which are toxic to aflatoxigenic Aspergillus spp., which could explain the bioactivity that resulted in reduced biomass in the neem-treated cultu res.