Enhanced Leaf Cooling Is a Pathway to Heat Tolerance in Common Bean

Area of Science:

• Plant Physiology
• Crop Science
• Climate Change Adaptation

Background:

• Common bean (Phaseolus vulgaris) is a globally important legume, crucial for protein in many regions.
• It is sensitive to high temperatures, posing a challenge due to ongoing global heating.
• Transpirational cooling is a known heat avoidance mechanism in crops, but its role in common bean is understudied.

Purpose of the Study:

• To investigate the extent and genotypic variation of transpirational leaf cooling in common bean.
• To determine if leaf cooling is functionally linked to heat tolerance in this crop.
• To provide tools for breeders to select for heat-tolerant common bean genotypes.

Main Methods:

• Explored the magnitude and genotypic variation of transpirational cooling in common bean.
• Compared leaf temperatures to air temperatures across different genotypes.
• Developed a model to simulate leaf temperature using air temperature and relative humidity.

Main Results:

• Common bean leaves are, on average, 5°C cooler than ambient air, with significant genotypic variation.
• Greater leaf cooling is associated with heat-tolerant genotypes, especially at elevated temperatures.
• Leaf cooling is largest at the top of the canopy, where heat stress is most critical during flowering.

Conclusions:

• Transpirational leaf cooling is a vital heat avoidance mechanism in common bean.
• Heat-tolerant common bean genotypes exhibit enhanced transpirational cooling, linked to higher stomatal conductance.
• The difference between air and leaf temperature can be used by breeders to screen for heat-tolerant common bean varieties.