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

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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 was detrimental when occurred during anthesis stage. Late sowing shifted the timing of heat stress, resulting in floral abortion and significantly reduced number of grains/spike. More importantly, some cultivars showed significant reduction following delaying sowing date, together with the strong correlation with yield especially at late sowing (r=0.74), imposing up to 42% yield penalty in the heat stressed late sowing conditions.

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 showed the strongest positive correlation in the 30 days late sowing with plant height (r=0.86), in the 15 days late sowing with number of total tillers/m ² (r=0.63) and in optimum sowing date with 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.