Pre–flowering Low Temperature Predisposition of Sorghum to Sugary Disease (Claviceps africana)

The relationship between pre–flowering climatic conditions and sugary disease incidence m sorghum was quantified over two seasons. In field trials with three male normal genotypes, low night temperatures 3—4 weeks prior to flowering increased susceptibility to the disease. Average night temperatures of <12 °C during the critical period resulted in male–normal genotypes being as susceptible as male–sterile genotypes. Seed set in uninoculated heads under pollination bags was also reduced, suggesting that increased susceptibility was the result of low temperature induced sterility. Genotypes differed in their ability to tolerate pre–flowering cold stress. Greenhouse and growth chamber trials confirmed that cold stress applied 7—8 weeks after planting reduced pollen viability and that this was the primary reason for increased susceptibility to sugary disease.