Distribution and occurrence of indigenous strains of atoxigenic and toxigenic Aspergillus section Flavi in groundnut producing areas of Southern Tanzania

Abstract

The objective of this study was to isolate and identify atoxigenic and toxigenic strains of Aspergillus section Flavi in southern Tanzania, and investigate possible application of atoxigenic strains in control of aflatoxin levels in groundnuts. Fungal communities in soils from groundnut fields were examined to see the distributions of aflatoxin-producing Aspergillus species and to spot endemic atoxigenic strains. Forty-five isolates belonging to Aspergillus section Flavi were collected randomly from soils of groundnut fields in three districts and characterized using morphological and physiological examination. Aspergillus section Flavi was detected in 40/45 (88.89%) of the soil samples collected in Mtwara, Tanzania. Members of Aspergillus section Flavi L-strain was the most common (79.5%), followed by S-strains (18.4%) and finally Aspergillus tamarii (1.8%). The mean colony forming unit (CFU) of the Aspergillus colonies per gram of soil was highly variable (p < 0.05) among the districts, ranging from 8.5×102 to 8.2×103 . The mean pH across the gathering sites additionally varied (pH 5.5- 6.8) which is within the optimal pH requirement for the members of Aspergillus section Flavi. Non-significant (p > 0.05) variation in temperature across the sampling sites was observed. The results also showed that Aspergillus flavus was detected in all the three districts. Atoxigenic strains have a potential value to be employed as biological control agents to mitigate aflatoxin in groundnuts.