Fungal colonization and decomposition of cereal straw

Abstract

The mycofloras of freshly harvested wheat and barley straw were assessed using direct and dilution plating methods and media of high and low water availability. Straw from the standing crop was predominantly contaminated with field fungi, including yeasts, mycelial yeasts and filamentous fungi such as Alternaria, Cladosporium, Epicoccum, Fusarium and Verticillium spp. However, chopped and baled straw had much greater populations of storage fungi, particularly Aspergillus and Penicillium spp., and Wallemia sebi. The dominant colonizers and rate of deterioration of straw held at different levels of water availability were determined over a period of 12 weeks at 15 and 25°C. At 15°C, and −7·0 MPa water potential (=0·95 water activity) Penicillium spp., were predominantly isolated; at −2·8 MPa (=0·98 water activity) Penicillium, Mucor, Rhizopus, Trichothecium and occasionally Fusarium spp. were present. Saturated straw was colonized rapidly by Mucor, Rhizopus, Penicillium, Stachybotrys, Fusarium and sometimes Trichoderma spp. At 25°C the patterns of colonization were different, particularly at 7·0 MPa water potential where Aspergillus spp. were dominant. The percentage dry matter lost over the 12 weeks varied with both temperature and water availability.