Positive response of maize husk traits for improving heat tolerance during flowering by alleviating husk inside temperature

Abstract

With the increase in high temperature intensity and occurrence frequency, heat stress has become the main threat to the production of majority of crops, including maize (Zea mays L.). Maize husks play protective and energy-providing roles in ear growth; however, the effects of the husk as well as the response of husk traits to heat stress are not fully understood. To address this gap, a series of experiments were conducted to explore the impacts of heat stress during flowering on husk inside temperature and husk functions and identify the difference in husk response between different tolerant genotypes. Husk inside temperature was lower than the air temperature, and the temperature difference between the outside and inside of the husk (Toutside – Tinside) increased with the increased air temperature and reached a maximum (2.5–3.0 °C) at 40/30 °C. The increased stomatal conductance and transpiration rate of husks could contribute to cooling the inside temperature under heat stress. Additionally, a higher husk inside temperature, larger yield losses, and decreased photosynthesis rate were found after manual removal of partial husks, which contributed to reduced husk protection and energy supply effects, especially exposure to heat stress. Under heat stress, heat-tolerant genotypes (i.e., lower yield losses) correspond to lower husk inside temperature, which could be related to the positive response of husk traits to heat stress, including increased/unchanged husk areas, length, width, weight and numbers. In contrast, heat-sensitive genotypes (i.e., higher yield losses) corresponding to higher husk inside temperature and reduction in the above husk parameters. Thus, husk traits that positively respond to heat stress can alleviate the increase in kernel temperature and further decrease yield damage. Considering appropriate husk traits and understanding the potential heat tolerance mechanism have implications for breeding and screening tolerant genotypes under future warmer climates.