OCCURRENCE OF AIRBORNE SPORES OF FUNGI CAUSING GRAIN MOLD OVER A SORGHUM CROP

Airborne spores of Fusarium, Curvularia and Alternaria species which cause sorghum grain mould were monitored over rainy season crops of the grain-mould susceptible sorghum hybrid CSH 1 using a Hirst spore trap. Spore trapping began at the flowering stage (GS 61) and was continued beyond grain maturity (GS 92). Spores of all three fungal genera were present during the post-flowering stages. However, more spores were trapped after the hard dough stage (GS 87) than at earlier growth stages. Spore content in the air increased after grain maturity (GS 92) under moist or humid conditions. Fusarium spores were most prevalent before dawn, whereas most spores of Alternaria and Curvularia were trapped during the day. The frequency of Fusarium and Alternaria spores in the two years differed while that of Curvaularia was similar in both years. The predominant species isolated from surface-sterilized moulded grain on malt-streptomycin agar were A. tenuissima, F. moniliforme, C. lunata and Phoma sorghina. These results prove that spores of mould causal fungi were naturally available in the air and initiated grain mould epidemics under suitable weather conditions.