Canopy architecture and leaf type as traits of heat resistance in pea

Pea (Pisum sativum L.) is sensitive to heat stress, and thus traits of heat resistance are desirable to minimize crop damage and maintain yield stability in improved cultivars. Crop research has focused on flowering and pollination success for heat resistant traits and vegetative structure is usually overlooked. The plant canopy, through leaf shape, plant habit and resistance to lodging, may offer additional sources of heat resistance in many crops. In pea, commercial cultivars have upright or vining plant habits, and either normal leaves comprised of stipules, leaflets and tendrils or semileafless leaves lacking leaflets. To determine the best canopy architecture and leaf traits associated with heat resistance, 24 diverse pea cultivars were tested in field trials across six environments in western Canada during 2014 to 2016. Compared to control conditions, heat stress increased canopy temperature from 24.9 °C to 27.8 °C and reduced reproductive stem length by 37% (17 cm), flowering duration by 21% (4.7 days), pod number by 30% (3 pods plant−1), and seed yield by 16% (54 g m-2). Pea cultivars had differential responses for measured traits; under heat stress conditions, semileafless cultivars with the upright habit had cooler canopies and greater seed yield, pod number and pod to node ratio than normal leafed vining cultivars. Lodging was associated with increased canopy temperature, a novel finding, implying greater heat stress. In contrast, growth and yield-related traits were greater in control environments for normal leaf, indeterminate and vining cultivars. Overall, the semileafless leaf and upright plant habit were superior traits that not only reduced lodging but maintained lower canopy temperatures in heat and drought stress environments. Therefore, vegetative heat stress can be avoided by management options that resist lodging and by selecting traits in plant breeding that can keep a cultivar upright.