Evaluating the Effect of Gamma Irradiation and Steam Sterilization on the Survival and Growth of Composted Sawdust Fungi in Ghana

The growth and survival of some fungi associated with composted and pretreated sawdust particularly for mushroom cultivation were investigated on two growth media; Cooke’s and Oxytetracycline Glucose Yeast Extract (OGYE). Some fungi were isolated during the composting of sawdust over a period of 28 days as well as after pretreatment with gamma irradiation doses of 5, 10, 15, 20, 25 and 32 kGy and moist heat of 100±2ºC for 2.5 hours. Fungal counts ranged 4.72- 5.77 log10 CFU/g and 3.4- 4.1 log10 CFU/g respectively for both media. Both pretreatment methods effectively reduced (p<0.05) fungal counts by an average of 1.48 (irradiation) and 2.22 (steam) log-cycle reductions on OGYE while there was an average of 3.13 (irradiation) and 1.10 (steam) log-cycle reduction on Cooke’s. Corresponding radiation sensitivities (D10 values) of 5.94±2.06 kGy and 5.64±1.12 kGy were recorded for fungi on both media respectively. Five species belonging to three genera were isolated on OGYE and among the fungi were Aspergillus niger, Aspergillus fumigatus, Aspergillus ustus, Mucor racemosus and Rhizopus stolonifer. Ten species belonging to four genera were also isolated on Cooke’s medium included Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Aspergillus ustus, Aspergillus terreus, Aspergillus parasiticus, Aspergillus alutaceus, Rhizopus stolonifer, Fusarium oxysporum and Mucor racemosus. There was an observed reduction (p<0.05) in species diversity after pretreatment. The presence of these microorganisms on sawdust also has serious repercussions on animal and human health.