Infection of sesame seed by Alternaria sesami (Kawamura) Mohanty and Behera and severity of Alternaria leaf spot in Kenya

Abstract

Infection levels of Alternaria sesami in sesame (Sesamum indicum L.) seeds collected from farmers in western districts of Kenya were detected using the oatmeal agar plate method. Infection levels varied from 9% in Kakamega to 24% in Siaya. Samples from Busia had a mean infection level of 11.69%. Alternaria leaf spot was monitored in plots planted with Alternaria sesami infected seed at six different infection levels at Kibwezi to determine the effect of transmission of the fungus by seed on disease severity. Increase in per cent leaf area blighted and per cent defoliation fit more closely the Gompertz model than the logistic model. Rates of disease increase in blighted leaf areas and defoliation, and areas under disease progress curves (AUDPC), varied among the six seed infection levels. Infection levels with larger AUDPC generally had faster rates of disease progress. Disease was most severe on plants established from seeds with 8% infection and least on plants established from seeds with 0% infection. Disease severity increased with increased seed infection level.