Vol. 9, Special Issue 11, Part P (2025)

Drought stress induces considerable variation in core physiological traits that regulate photosynthetic efficiency, water-use dynamics and adaptive responses in groundnut. Understanding the inheritance of these traits across generations is essential for developing drought-resilient cultivars. The present study evaluated five key physiological determinants viz., SPAD chlorophyll meter reading, water-use efficiency (WUE), specific leaf area (SLA), number of stomata and stomatal conductance, across six generations (P₁, P₂, F₁, F₂, BC₁ and BC₂) under irrigated and drought-stress conditions. Generation mean analysis was employed to assess the magnitude of genetic effects governing the inheritance of these traits.

Analysis of variance revealed significant differences among all six generations under both environments, highlighting the availability of substantial physiological variability. F₁ means were mostly intermediate or superior to both parents, indicating partial to complete dominance for several traits related to chlorophyll retention, stomatal behaviour and leaf structural characteristics. Under irrigated conditions, the high-yielding parent performed better for SLA and stomatal conductance, while the drought-tolerant parent exhibited superior SPAD values and WUE under stress. BC₂ (F₁ × ICG 4670) recorded the highest SPAD, WUE and optimal stomatal adjustment under drought, whereas BC₁ (F₁ × TAG-24) demonstrated better performance under irrigation.

The simple additive dominance model was insufficient; therefore, a six-parameter model was used. Significant A, B, C and D scaling tests and joint scaling test results indicated the presence of epistatic interactions. Under irrigated conditions, dominance (h) and dominance × dominance (l) interactions were prominent for SLA, stomatal conductance and number of stomata, suggesting the prevalence of non-additive gene action. Under drought stress, dominance and dominance × dominance effects again dominated for SPAD and WUE, traits central to maintaining photosynthetic stability and water-use efficiency under limited moisture. These outcomes suggest that hybridization followed by delayed selection would be more effective for improving non-additive traits.

Additive (d) and additive × additive (i) gene effects were significant for WUE, SPAD and number of stomata, indicating that early-generation selection could be feasible for traits with more fixable inheritance. Duplicate epistasis was more frequent than complementary epistasis under both environments, implying that mild selection in early generations and stronger selection pressure in advanced generations would enhance breeding progress.

Overall, this study emphasizes the importance of integrating key physiological traits, particularly SPAD, WUE and stomatal behaviour into breeding programmes to accelerate the development of drought tolerant groundnut genotypes.