Impact of sowing date and irrigation regime on wheat performance under heat and drought stress in the Indo-Gangetic plains of Bihar

Wheat (Triticum aestivum L.) is a staple crop in the Indo-Gangetic Plains, where rising temperatures and limited water availability threaten productivity. A field experiment was conducted during the 2022–23 rabi season at Dr Rajendra Prasad Central Agricultural University, Pusa, Bihar, to evaluate six wheat genotypes under three contrasting conditions: normal sowing with full irrigation, late sowing to induce terminal heat stress and normal sowing with restricted irrigation (single irrigation at 45 days after sowing ). Morphological, phenological and yield traits were assessed, including plant height, spike and peduncle length, days to heading, flowering and maturity and grains per spike. Late sowing markedly accelerated phenology and reduced grains per spike by up to 38 %, whereas restricted irrigation delayed maturity and reduced grains per spike by up to 31 %. Genotypic differences were evident: DH5-167 exhibited strong vegetative resilience but low reproductive performance, while IC-252874 maintained higher grains per spike despite moderate vegetative susceptibility. Multivariate analyses revealed that the first two principal components explained 86.38 % of the total variation. Genotypes were separated primarily according to treatment along these components, indicating a stronger influence of environmental stress on phenotypic expression than genotype. Overall, the results highlight a trade-off between vegetative growth and reproductive stability under abiotic stress and suggest that combining traits conferring reproductive resilience to heat with those prolonging grain filling under drought can enhance yield stability in wheat grown in the Indo-Gangetic Plains.