Preharvest seed infection by Aspergillus flavus group fungi and subsequent aflatoxin contamination in groundnuts in relation to soil types

Preharvest seed infection by Aspergillus flavus and aflatoxin contamination in selected groundnut genotypes (four A. flavus-resistant and four A. flavus-susceptible) were examined in different soil types at several locations in India in 1985-1990. Undamaged mature pods were sampled at harvest and seed examined for A. flavus infection and aflatoxin content in two or more trials at ICRISAT Center on light sandy soils and red sandy loam soils (Alfisols), and on Vertisols, at Anantapur on light sandy soils, and at Dharwad and Parbhani on Vertisols. Rainy season trials (1985-1989) were all rainfed. Post-rainy season trials were irrigated; late-season drought stress (90 days after sowing (DAS) until harvest at 125 DAS) was imposed in the 1987/88 and 1989/90 seasons. A. flavus infection and aflatoxin contamination levels were much lower in seed of all genotypes from Vertisols than in seed from Alfisols across locations and seasons. Vertisols also had significantly lower populations of A. flavus than Alfisols. There were no marked differences between light sandy soils and red sandy loam soils (Alfisols) in respect of seed infection by A. flavus and aflatoxin contamination. Significant interactions between genotypes and soil types were evident, especially in the A. flavus-susceptible genotypes. Irrespective of soil types, A. flavus-resistant genotypes showed lower levels of seed infection by A. flavus and other fungi than did A. flavus-susceptible genotypes. The significance of the low preharvest aflatoxin risk in groundnuts grown on Vertisols is highlighted.