Genotype x environment effects on the response of sorghum to ergot and repercussions for disease screening

Ergot, caused by Claviceps africana, is a disease of unfertilized sorghum ovaries. Weather during two critical phases of flowering usually determines ergot incidence and severity. Low night temperatures during the 3-4 weeks preflowering reduce pollen viability and predispose florets to infection. Sorghum genotypes differ in terms of critical threshold temperatures. Similarly, weather during early anthesis affects ergot severity. The optimum temperature for infection and disease development is 19degreesC, with a limited risk of infection above 28degreesC. Humidity also has a significant effect on the disease x temperature relationship. The relationship between weather and ergot severity can be used to model the ergot potential of a specific flowering date. Significant differences in the ergot potential required to induce infection, termed the Ergot Breakdown Point (EBP) and determined by nonlinear regression analysis, are known and can be used as a measure of escape resistance.