The frequency and distribution of the fungi associated with western hard red spring wheat seed degraded due to mildew

Abstract

Hard red spring wheat (Triticum aestivum) seed samples with various levels of a degrading factor known in the trade as mildew were collected for 3 years from primary elevators in the prairie provinces. Samples were examined for viability and the presence of seed-borne fungi. Members of 32 fungal genera were isolated, with Alternaria spp. and Cladosporium spp. the most frequently isolated taxa. When the mycoflora of seeds displaying the mildew discoloration was compared with the mycoflora of the heterogenous mixture of seeds in the original sample from which they had been selected, only Cladosporium spp. showed a significant increase in frequency. The geographic origin of the samples influenced the frequency of a number of fungi. It appears prolonged wet weather at crop maturity bleaches the kernels and stimulates further growth of fungi, primarily Alternaria spp. and cladosporium spp., at the exposed brush end of the seed. This growth discolors the kernels producing what is termed mildew. However, it is primarily the wet harvest weather which affects the actual end-use of the grain. The fungus induced discoloration and the bleaching of the kernels serve the grain inspectors as visual indicators of damp harvest conditions. Although the principle of degrading grain due to the presence of mildewed kernels is soundly based on actual quality reduction, it is suggested that a less ambiguous and more descriptive term such as grey-brush be used.