Physiological selection of wheat synthetic back derived lines for drought and heat tolerance

Abstract

Drought and heat stress are major constraints to wheat production, necessitating the identification of genotypes with superior physiological mechanisms for stress adaptation. The present study evaluated 200 synthetic backcross-derived lines (SBLs) for drought and heat tolerance using germination, physiological, and yield-related traits. For drought screening at the germination stage, seeds were exposed to 20% polyethylene glycol (PEG-6000), and germination percentage, shoot length, and root length were recorded. Significant variation was observed among SBLs, with germination ranging from 0 to 100%. Forty-seven SBLs exhibiting high germination also showed greater seedling biomass. Greenhouse evaluation of 193 SBLs and the check variety NARC-2009 under drought stress identified 31 SBLs as drought tolerant based on grain weight per spike, thousand-kernel weight, and relative water content (RWC). These lines exhibited only 10–20% relative yield reduction compared with 25–50% in the remaining lines. Heatmap and correlation analyses demonstrated positive associations of RWC and membrane stability index (MSI) with thousand-kernel weight, indicating their potential as reliable physiological indicators of drought tolerance. For heat tolerance assessment, plants were exposed to 40 °C for 5 h daily at the post-anthesis (milky) stage. Based on yield and physiological responses, 45 SBLs showed minimum reductions in grain weight under heat stress. These lines maintained higher grain weight per spike and thousand-kernel weight and exhibited greater proline accumulation. Correlation analysis further revealed a positive association between proline content and thousand-kernel weight under heat stress. Conclusively, the study identified promising SBLs with superior drought and heat tolerance and demonstrated that RWC, MSI, and proline accumulation are useful physiological traits for screening wheat germplasm. The selected lines may serve as valuable genetic resources for wheat breeding programs aimed at developing climate-resilient cultivars with improved productivity under drought and heat stress. © 2026 The Author(s)