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Department of Seed Science and Technology, S.V. Agricultural College, ANGRAU, Tirupati-517 502.
Sesame (Sesamum indicum L.) is an important oilseed crop valued for its high oil and protein content, widely cultivated in semi-arid tropical regions. Among the various diseases affecting sesame, Alternaria leaf spot caused by Alternaria spp. is a significant constraint, leading to considerable yield losses. This study evaluated the response of 30 sesame genotypes, including germplasm lines, released varieties, and checks, against Alternaria leaf spot under natural field conditions during the kharif 2024 season at S.V. Agricultural College, Tirupati. Disease severity was assessed using the standardized 0-9 rating scale (Mayee and Datar, 1986) at 15-day intervals, and Percent Disease Index (PDI) along with the apparent rate of infection (r) were calculated. Results revealed variation in disease reaction, with no genotypes showing immune or resistant response. Twenty genotypes exhibited tolerance with PDI values ranging from 12.74% to 25.50%, while 10 genotypes were susceptible, with PDI ranging from 27.45% to 44.10%. The highest apparent rate of infection (r = 0.49) was observed in the susceptible check viz., SI- 2174-1, indicating a potential for epidemic development in susceptible genotypes. Disease symptoms initiated around 45 days after sowing and progressed from leaf spots to stem and pod lesions, significantly impacting seed quality and yield. The study highlights considerable genetic variability for Alternaria leaf spot tolerance in sesame germplasm, underscoring the need for incorporating tolerant genotypes in breeding programs. The findings also emphasize the influence of environmental factors and crop management on disease development.
KEYWORDS: Sesame, Alternaria leaf spot, Alternaria spp, Percent disease index, Apparent rate of infection.