Aspergillus species groundnut seed invasion as influenced by soil solarization and time of planting

Aflatoxin contamination of groundnut is a serious problem in most groundnut-producing countries where the crop is grown under rainfed conditions. Field experiments were conducted at two locations to determine the effect of soil solarization on Aspergillus spp. inocculum in the soil and to evaluate the effect of soil solarization and time of planting on Aspergillus spp. seed invasion and yield of groundnut varieties. Soil samples were taken in three rounds and analyzed for aflatoxigenic population. Soil solarization reduced fungal inoculum and increased groundnut yields. Individual and total cfu g-1of soil was determined before, after solarization and at harvest. Four Aspergillus species namely, A. flavus, A. parasiticus, A. niger and A. terreus were identified and their densities were significantly (P<0.05) reduced at after solarization. In the solarized plots, A. flavus and A. parasiticus were found reduced by 53.8 and 45% cfu g-1 at Ramma and 36.4 and 44% cfu g-1at 5 and 10 cm soil depths at Mayweyni, respectively, after soil solarization in the solarized plots than the nonsolarized plots. At harvest, Fusarium spp., A. flavus and A. terreus were detected. Three Aspergillus species namely, A. flavus, A. niger, and A. parasiticus were isolated from seed samples plated on Czapek-Dox Agar medium. Early planting of the varieties showed the lowest level of seed infection by A. flavus (22.8%).