Abstract
The effectiveness of neem (Azadiracta indica) oil on the growth, morphology, sporulation, viability of spores, aflatoxin B1 and B2 production by A. flavus on Yeast Extract-Sucrose medium was determined. Neem oil inhibited the fungal growth (i.e. mycelia dry weight, diameter of colony and growth rate) on solid media at concentrations from 0.5 to 5.0% v/v, although it significantly increased sporulation in the same conditions. Spores obtained from cultures grown without neem oil reduced germination when incubated in a neem oil supplemented medium. Colonies grown on solid media and in submerged cultures in the presence of neem oil exhibited morphological alterations, including granular cytoplasm, atypical hyphae branching pattern, abnormal and undifferentiated conidiophores. High Performance Liquid Chromatography was used to measure aflatoxins. In submerged cultures, neem oil at concentrations from 0.5 to 4.0% v/v caused approximately 95% inhibition in Aflatoxin B1 and B2. On other hand, these conditions failed to suppress fungal growth. Current research emphasized that neem oil was not fungistatic or fungicidal, but exhibited anti-aflatoxigenic activity.
Highlights
Aflatoxins are polyketide secondary metabolites produced by toxigenic strains of Aspergillus section Flavi group: Aspergillus flavus, A. parasiticus, A. nomius, A. tamarii and A. bombysis
Bankole [31] showed that the Neem Seed Oil (NO) at 1000 ppm was able to block the Aflatoxin B1 (AFB1) synthesis by Aspergillus flavus inoculated in maize grain
Similar results were found by Zeringue and Bhatnagar [7], where the application of aqueous extract from neem leaves in cotton balls infected with Aspergillus flavus, was able to inhibit up to 98% the AFB1 production, without reducing the mycelial growth
Summary
Aflatoxins are polyketide secondary metabolites produced by toxigenic strains of Aspergillus section Flavi group: Aspergillus flavus, A. parasiticus, A. nomius, A. tamarii and A. bombysis. Bhatnagar and co-workers have demonstrated that blended neem leaf extracts inhibited aflatoxin production by A. parasiticus and A. flavus, but they failed to affect fungal growth [6,7]. Neem leaves contain specific volatile compounds with fungicidal properties This complex mixture of volatiles affected both fungal growth and aflatoxin production in A. parasiticus [8]. The main chemical fractions of neem oil with antifungal activities are a mixture of triterpenoidal and tetranortriterpenoid compounds. There is scanty information available in the literature on the effect of neem oil on growth, sporulation level and aflatoxins production by A. flavus in submerged cultures. Current study determines the effectiveness of neem oil on the growth, morphology, sporulation, viability of spores and AFB1 and AFB2 production by A. flavus on a semi-synthetic medium
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