The normal mycoflora of commodities from Thailand. 2. Beans, rice, small grains and other commodities

Abstract

Part of a comprehensive study of fungi occuring in commodities in Thailand, this paper reports results from 276 samples of mung beans, rice, sorghum and soybeans as well as other minor crops. Samples for major commodities were taken from farmers' stocks, middlemen and retail outlets, while those for minor crops were mostly from retail. Each sample was divided into two portions, one being examined in Bangkok and thesecond at North Ryde. Mycological examinations were carried out by direct plating after surface disinfection in chlorine. Media used were dichloran rose bengal chloramphenicol agar, dichloran 18% glycerol agar, Aspergillus flavus and parasiticus agar and dichloran chloramphenicol peptone agar. Fungi were identified to species level and percentage infection of samples calculated. The dominant fungus found in mung beans was Fusarium semitectum, which was present in 40% of samples and at a high level (18% of all seeds) overall. Aspergillus flavus was also found in 40% of samples, but only in 2% of seeds overall. Lasiodiplodia theobromae was the only other fungus exceeding 1% total infection. The major fungi found in soybeans were A. flavus (67% of samples; 6% overall) and Cladosporium cladosporioides (49% of samples; 9% overall). Storage fungi were more common in soybeans than the other commodities, indicating longer or longer or adverse storage. Paddy rice contained high levels of a wide variety of field fungi, notably Fusarium semitectum, Bipolaris oryzae, and Curvularia, Phoma and Colletotrichum species. However, probably due to the heat generated by milling, milled rice contained very few fungi, which were mostly of storage origin. Only 3% of particles examined contained internal fungi. Infection in sorghum was typical of oilseeds, dominated by Aspergillus flavus, which was present in 86% of samples, with an overall infection rate of 12%. Beans other than soybeans were infected by a wide range of field fungi, but at low levels, with less than half of seeds examined being infected internally. With the exception of sorghum, the levels of mycotoxigenic fungi encountered were much lower than observed previously in nuts and oilseeds.