Heat Stress Adaptation in Elite Lines Derived from Synthetic Hexaploid Wheat

The contribution of synthetic hexaploids in spring wheat (Triticum aestivum L.) breeding has been documented under drought stress, but not previously under heat stress. A set of six advanced wheat lines derived from synthetic hexaploid wheat (ASD) was compared to their conventional hexaploid (Conv-Hex) and synthetic derivative (Syn-Der) parents under three different temperature scenarios in the field (temperate or non-stress, heat-stress environment, and late-or extreme heat environment). The ASD lines showed a yield advantage under heat and extreme heat stress compared to the best parent (Syn-Der) by on average 15 and 13%, respectively, while the average yield advantage under temperate conditions was just 5%. A similar pattern to yield was observed for grain number, while individual kernel weight of ASD lines was similar to the best parent (Syn-Der) in all three environments. The ASD lines expressed on average 12% more final biomass than the best parent (Syn-Der) under heat environment, but similar biomass to them at temperate and extreme heat environments, respectively. Physiological traits related to heat tolerance included higher crop growth rate, increased water-soluble carbohydrates (WSC) storage in stems, cooler canopy temperature, and spectral indices which are related to pigment composition, photo-protective mechanisms, and radiation use efficiency. These traits enabled a larger number of grains to be set, in addition to growth of taller stems with a greater WSC storage capacity that was significantly related to kernel weight. Results reinforce the positive impact of using synthetic wheat in plant breeding for climate change.