Isolates of Aspergillus and Fusarium isolated from grain samples (barley, rice, wheat, white corn and yellow corn), collected from different localities of Riyadh region, Kingdom of Saudi Arabia, were screened for their toxigenic potential. Potato dextrose agar (PDA), yeast extract sucrose (YES) broth and white corn grains were suitable media for production of aflatoxins and trichothecenes by Aspergillus and Fusarium isolates, respectively. Composition of media, fungal species and isolates had an important role in the production of toxins. PDA was the most suitable medium for production of aflatoxins and trichothecenes. A flavus strain 4 produced the highest amount of aflatoxins in PDA and corn grains media, whereas in YES broth A. flavus strain 2 was the most active producer. On the other hand, F. sporotrichioides strains 2, and 3 and F. equiseti strain 1 produced the highest amount of trichothecenes in PDA, corn grains and YES media, respectively. In addition, more than one toxin was found in growth culture of the toxigenic fungi in most cases, which may be an important factor in pathogenicity. Aspergillus and Fusarium toxins retarded emergence and growth of white corn seedlings, as well as biosynthesis of photosynthetic pigments. Root was more susceptible to fungal metabolites than shoot. Aspergillus toxins were more virulent against white corn seedlings than Fusarium toxins. Generally the degree of severity was directly correlated with toxin concentrations.
Key words: Aspergillus, Fusarium, aflatoxins, trichothecenes, phytotoxicity
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