Field transmission efficiency of Alternaria sesami in sesame from infected seed
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Four sesame accessions with varying levels of susceptibility to Alternaria sesami were selected from an advanced germplasm collection of the Sesame Improvement Project to determine transmission efficiency of A. sesami from seed under field conditions. Accessions were sown in field plots in Siaya, Kenya, in March and October 1995 during the first and second rainy seasons, respectively. Incidence of Alternaria leaf spot (ALS) following artificial inoculation averaged 85–95% for all accessions in the two seasons. Infection of A. sesami in harvested seed averaged 11.8% for accessions SPS SIK 013, 9.4% for SPS SIK 110, 9.7% for SPS SIK 121 and 6.8% for SPS SIK 130. Three hundred seeds from the harvested seed lots for each accession were sown in disease-free field plots at Kibwezi, Kenya, in March and October 1996 for two seasons. Typical disease symptoms appeared about 5–6 weeks after sowing. Disease progress curves were better described using the Gompertz rather than the logistic model for all the accessions evaluated. Disease onset (Yo) was nearly the same in both seasons but the rate of disease increase (r) was faster in the first season than in the second season. Rate of disease progress was consistently higher for SPS SIK 013 than SPS SIK 130, in both seasons. Area under the disease progress curves for accessions was significantly higher (P<0.01) in the first season compared to the second season. Disease incidence averaged 0.0% for SPS SIK 110, 1.5% for SPS SIK 130, 3.3% for SPS SIK 121, and 3.6% for SPS SIK 013. Transmission efficiency of ALS by seed ranged from 0.0% to 40.7% and was significantly higher for SPS SIK 013 and SPS SIK 121 than for SPS SIK 110 in the two rainy seasons.