Severity of Alternaria leaf spot and seed infection by Alternaria sesami (Kawamura) mohanty and behera, as affected by plant age of sesame (Sesamum indicum L.)

Alternaria leaf spot incited by Alternaria sesami, was monitored to determine the effect of plant age on disease severity and seed infection by A. sesami in plots containing sesame accession SPS SIK 110 plants of five different ages. The increase in percentage leaf area blighted and percentage defoliation fit the Gompertz model more closely than the logistic model. Rates of increase in blighted leaf area and defoliation, and areas under disease curves (AUDPC) varied among the five different plant ages. Plant ages with larger AUDPCs generally had faster rates of disease progress. Plants inoculated at 8 and 12 weeks of age were most susceptible to the disease and those inoculated at 4 weeks exhibited the least susceptibility. Seed infection was determined by the oat-meal agar plate method and the infection was highest in plants infected at 8 and 10 weeks of age and least in plants infected at 4, 6 and 12 weeks of age.