The role of drought stress on aflatoxin contamination in groundnuts and Aspergillus flavus population in the soil during field production

Drought stress is one of the factors that contribute to aflatoxin contamination in groundnuts during field production. A study was conducted aimed at investigating the effects of drought on aflatoxin contamination and A. fluvus population in Malawi. Four drought stress levels; prolonged (4 weeks), min (3 weeks), mild (2 weeks) and no drought were imposed on five groundnut varieties at pod filling stage. Soil samples were collected from each plot four times; at planting, beginning of drought, end of drought and at harvest. The groundnut grain samples were prepared and analyzed for aflatoxin contamination using Mobile assay tablet reader and neogen strips. A. flavus population densities in soil samples collected from the plots were estimated using serial dilutions plated on A. Aspergilli medium (selective media called dichloronitroaniline Rose Bengal (MDRB). There were significant differences (p=0.011) in aflatoxin contamination among drought stress levels. High contamination was observed in treatments under prolonged drought (22.0 ppb) while low contamination was observed in samples under no drought (1.5 ppb). None of the varieties used in the study were resistant or susceptible to aflatoxin contamination under drought or adequate moisture. The results also showed that there were significant effect of drought period and harvesting time for A. flavus population. There was high population of A.flavus in prolonged drought at end of stress and harvesting, 8511 and 6044 cfu/g of soil, respectively. It was concluded that drought contributed to aflatoxin contamination in groundnuts and also increased A.flavus population in soil during drought period and also at harvesting.