Screening Indian mustard genotypes for terminal heat stress tolerance using morphological traits and yield-based indices

Abstract

Abiotic stresses, especially high temperatures, strongly limit the yield of Indian mustard (Brassica juncea L.). Heat during flowering and grain filling damages cell membranes, disrupts movement of photosynthates and leads to shrivelled seeds. This study assessed 44 genotypes of Indian mustard under timely and late sowing. A wide set of traits were recorded viz. plant height, branching, siliqua traits, seed yield, oil content, canopy temperature depression (CTD), membrane stability index (MSI), and stress indices (HSI, YSI). Late sowing caused large reductions in secondary branches (26.95%), siliqua per plant (23.88%), seed yield per plant (24.79%), seed yield per plot (23.79%), and MSI (21.17) while days to 50% flowering and CTD increased, indicating stress escape and adaptive cooling. Genotypes BRBJ 25, BRBJ 41, and BRBJ 44 showed minimal yield loss (<3%), highest YSI (0.98) and very low HSI (~0.10), confirming strong heat tolerance, whereas BRBJ 47 suffered the greatest yield penalty (40.55%). Secondary branches, siliqua per plant, CTD and MSI emerged as key selection traits and BRBJ 44, BRBJ 41, BRBJ 29, BRBJ 45 and BRBJ 25 were identified as promising donors for breeding terminal heat stress tolerant Indian mustard.