Resistance to Cercospora Leaf spot disease and combining ability of selected Sesame (Sesamum indicum L.) lines in Uganda

Abstract

Cercospora leaf spot disease is one of the major diseases affecting sesame production in Uganda causing yield losses of between 22-53%. This study was conducted to evaluate response of selected sesame genotypes to Cercospora leaf spot disease (CLS) and determine the combining ability to the disease among them. To identify sources of resistance to Cercospora, 30 genotypes were screened for resistance to CLS at Abi Zonal Agriculture Research and Development Institute (Abi ZARDI) in Arua and National Semi Arid Resources Research Institute (NaSARRI) in Serere, Uganda under natural conditions of infection. An alpha lattice design of 6 blocks by 5 genotypes was used in each of the environments with three replications. The disease severity was scored visually using a scale of 1-7 of four middle rows per plot at 56 DAP, 70 DAP and 84 DAP. Analysis of variance for CLS across sites showed significant difference (p<0.01) among genotypes. None of the thirty genotypes was immune or highly resistant. Their response was, one genotype was resistant, thirteen genotypes were moderately resistant, fifteen genotypes were moderately susceptible and one genotype was susceptible. These sources of resistance can be used to impart resistance to CLS in sesame. To study combining ability to CLS, nine sesame genotypes with varying levels of resistance previously identified were crossed in a half diallel mating design. The study revealed that general combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant (P≤0.001) for severity of Cercospora leaf spot disease, days to 50% flowering and yield. The ratio of variance component of GCA to SCA was less than one for all the traits studied indicating non additive gene action. Three parents Sesim1 (-2.3***), Ajimo A1-5 (-0.11***) and Renner 1-3-17-1 (-2.4***) were the best combiners for disease resistance and their hybrids P1xP6 (-0.72*), P2xP3 (-0.58*), P5 xP8 (-0.62*) had negative SCA effects implying high level of disease resistance. For yield, parents Sesim2 (4.61***), Renner 1-3-1-17-1(4.38***), Sesim1 (2.77***) had positive GCA effects as well as their hybrids P1xP7 (31.46**), P1xP8 (27.12**), P2xP5 (29.00**) and P2xP6 (19.54*) suggesting their ability to yield highly. Parents Sesim1 and Renner 1-3-1-17-1 were the best combiners for both disease resistance and yield hence these parents can be used to improve both traits in sesame simultaneously. Non additive gene action implies that selection for these traits needs to be delayed at later stages of segregation.