Investigation on the toxicity of fungi from rootstock snacks

Chicken embryo bioassay was used to monitor the toxicity of extracts from rootstock snack samples during a 210-day storage period. Results show that the relative toxicity values which were initially very low increased significantly as from 120th day (when 32% mortality was recorded) up till the last day when 73% was obtained. Toxicity of extracts from axenic cultures of 12 fungal species isolated from the snack samples was also determined. The strains of Aspergillus chevalieri, Rhizopus nigricans and Rhizopus sp investigated were nontoxic. A. niger, A. flavus, A. fumigatus, Penicillium chrysogenum, A. parasiticus, P. citrinum, A. ochraceus, Fusarium monifilorme and A. candidus were found to be toxic in decreasing order of potency as recorded after 30 days of growth at room temperature on substrate of 0.90 water activity level. Trends in the moisture content levels, pH and the incidence of fungal growth on the snack samples were also studied. Results suggest that storage for a period not exceeding 90 days and maintenance of safe moisture level would control mould growth and the associated mycotoxins in the snack.