Booting heat stress alters leaf photosynthesis, growth rate, phenology and yield in rice

Background: The phenomenon of global warming results in a significant rise in temperature which adversely affects the growth, physiology, and yield of rice. In order to gain insight into the impacts of booting heat stress (at 42 degrees C, 3 h for 7 days), we investigated its effect in three rice genotypes, namely, N22, KDML105 and IR64. Results: Booting heat stress caused an extended phenology and a lower photosynthesis and plant growth rate but an increase in chalkiness. Although, the prolonged phenology from dough to physiological maturity resulted in a longer duration of grain filling, the adverse effects of this were a significantly lower yield component, yield and harvest index across all varieties of rice. Among cultivars, N22 demonstrated an adapted ability to maintain leaf gas exchange and compensated for the vegetative part by an increase in tiller numbers resulting in a less affected growth rate. It caused extended grain filling by prolonging the phenology. Consequence, N22 had the lowest reduction in number of seed panicle 1, number of filled seeds hill 1, yield, harvest index, and percentage chalkiness. KDML105 was adapted to booting heat stress by maintaining leaf gas exchange, increasing specific leaf area and prolonging phenology. The longest extended phenology and high photosynthesis during dough grain were associated with moderate yield reduction and chalkiness. Nonetheless, IR64 demonstrated significant reductions in photosynthesis, growth rate, and yield but the highest percentage of grain chalkiness. Conclusion: Therefore, the response of N22, KDML105 and IR64 to booting heat stress could be indicated as being heat tolerant, moderately heat sensitive, and heat sensitive, respectively. This approach can be applied to crop modeling and rice heat tolerance in breeding programs.