Effects of physical preservation methods on sclerotial germination in Aspergillus flavus and Aspergillus ochraceus in stored grain

Abstract

Germination of sclerotia of Aspergillus flavus and Aspergillus ochraceus was assessed following gamma irradiation during exposure to different levels of relative humidities or to various modified atmospheres. The effect of combined treatments on germination was also studied. No sclerotia of either fungi germinated following irradiation with 2.5 kGy. At 80% relative humidity, germination was almost completely inhibited during 50 days of exposure. Sclerotia of A. flavus were found to tolerate higher levels of CO2 than those of A. ochraceus, and 100% germination of the former, but not the latter, occurred at 80% CO2 (given with either 20 or 5% O2). Germination of A. flavus sclerotia was markedly reduced only at modified atmospheres of 40% CO2 and 1% O2. Working with two sublethal dosages of gamma irradiation, 1.0 and 1.5 kGy, it was demonstrated that less CO2 was needed in the atmosphere (with 20% O2) to reduce germination as the irradiation dosage increased. The advantages of the combined treatment compared with each treatment applied alone are discussed. Key words: sclerotia, germination, Aspergillus, inhibition, physical methods.