Evaluation of Morphological and Physiological Traits in Sesame (Sesamum indicum L.) Associated with Resistance to the Mirid Bug (Nesidiocoris tenuis)

Abstract

Sesame (Sesamum indicum L.) production is increasingly affected by the mirid bug (Nesidiocoris tenuis), emphasizing the need to identify traits associated with host plant resistance. An initial screening of 58 sesame genotypes under natural field infestation identified 15 representative genotypes for more detailed analysis. These 15 genotypes included 4 resistant, 5 moderately resistant, 4 susceptible, and 2 highly susceptible, selected proportionally based on the mean Nesidiocoris tenuis population per plant across all 58 genotypes tested, grouped into four resistance categories. Mirid bug populations were tracked at different crop growth stages by counting insects on randomly chosen plants within each replication. Morphological traits, including plant height, number of capsules per plant, and leaf thickness, were recorded at maturity. Physiological traits, including relative water content (RWC) and water saturation deficit (WSD), were measured at crop maturity, and chlorophyll content was measured at 30, 45, and 60 DAS to examine their association with mirid bug infestation. All traits showed significant genetic variation. The mirid bug population had strong negative correlations with plant height (r = −0.868), capsule number per plant (r = −0.922), and leaf thickness (r = −0.847), and a significant positive correlation with RWC (r = 0.848). WSD had a strong negative association (r = −0.861). Chlorophyll content was moderately related to mirid bug presence at 45 DAS but showed weak correlations at other stages. These results indicate that differences in morphological and water-related physiological traits, particularly RWC and WSD, affect the level of host resistance to mirid bug infestation. These traits could be valuable criteria for selecting and breeding pest-resistant sesame varieties.