Associated fungi within maize kernels and their control

This research was conducted to study the fungal deterioration and aflatoxins production of stored maize grains under different storage conditions of temperature ((refrigerator and room) and relative humidity (45, 65 and 85% RH) as well as storage periods up to three months. The commercial maize hybrids were screened for their susceptibility to Aspergillus .flavus infection and aflatoxins production under field conditions. Also, gamma irradiation and medicinal plant extracts were tested for their capability to decrease the deterioration and aflatoxins accumulation in stored maize grains .Several fungal species were isolated from maize grains collected from 6 Egyptian governorates. Fusarium verticillioides followed by A. flavus and Penicillium spp. were the most dominant fungi. The most contaminated samples were collected from Kafr El-Shiekh followed by Beheira and Beni-Suef governorates. Only, 6 out of 15 isolates of A. flavus and 3out of 9 isolates of A. parasiticus were able to produce various amounts and/or types of aflatoxins when chemically analysed by TLC technique. AFB I was produced in all 9 isolates. The frequency of A. flavus and other associated fungi with maize grains stored up to 3 months was increased with the increasing of relative humidity and extension of storage period either in artificially inoculated grains by A flavus or in the check treatment .Generally, it was more at room temperature than in the refrigerator. Moisture content was increased with increasing RH and prolonging of storage period either in inoculated or uninoculated grains, and it was more in room temperature. Grains viability was decreased by increasing storage period at any storage condition. Biochemical analysis of stored grain contents showed gradual reduction in total soluble sugars, non-reducing sugars and total lipid contents, meanwhile reducing sugars and acid value were increased in quantity by the prolongation of storage period. At room temperature, aflatoxins levels were increased under all storage conditions meanwhile, no aflatoxins were produced in refrigerator stored samples. Amongst the tested maize genotypes, the single cross SC10 showed the highest degree of resistance to A. flavus infection and aflatoxins production. Grains irradiated with or 10 kGy effectively reduced the infection with A. flavus and other contaminated fungi for up to 3 months of storage. Also, these treatments greatly reduced aflatoxins (B1 and B2)production in comparison to un-irradiated grains. Application of different concentrations of chloroform-methanol and/or aqueous extracts of thyme, tooth pick, spider flower and tooth-brush caused significant reduction in the in vitro growth of A.flavus. Chloroform-methanol extracts of tooth pick caused the highest reduction followed by thyme extract. Moreover application of maize grains with chlorofornl-methanol extracts of thyme and tooth pick, before storing for up to 20 to 60 days, have greatly reduced the frequency of A. flavu and other associated fungi as well as the aflatoxins production.