Assessment of Spring wheat responses to late season heat stress under Mediterranean conditions

In Mediterranean climatic regions, wheat yield is significantly influenced by sowing date and cultivar selection, particularly where production could be limited by heat waves during critical growth stages. This investigation was undertaken to determine the effect of shifting sowing date on a cohort of six high yielding spring wheat cultivars (Triticum aestivum L.), by delaying sowing date 15 and 30 days in a two-year field trial, aiming to highlight agronomic traits contributing to sustained yield potential under heat stress induced by late sowing, with a focus on identifying tolerant cultivars. Our findings showed that heat stress during grain filling was less detrimental compared to its occurrence during anthesis. Late sowing shifted the timing of heat stress, resulting in floral abortion and significantly reduced number of grains/spike, consequently imposing 42% yield penalty, underscoring number of grains/spike stability as key factor to sustain yield under heat stress during anthesis. On the contrary, harvest index of sowing delayed by 30 days was significantly higher compared to both 15 days late sowing and the optimum sowing date, suggesting that decline in biological yield exceeded that of grain yield. Upon shifting sowing date, the strength of traits association is altered, grain yield associations strongest positive correlation in the 30 day late sowing was plant height (r=0.86), in the 15 days late sowing was number of total tillers/m2 (r=0.63) and in optimum sowing date was biological yield (r= 0.62), suggesting that grain yield enhancement through selected traits with direct or indirect contributions should be evaluated independently across different growing conditions.