Identification of Canopy Cooling Traits for Heat Tolerance in Peas.

Pea (Pisum sativum L.) is a cool season legume crop mainly grows in semi-arid temperate conditions. Western Canada is a leading producer and exporter of dry peas. However, most of the existing cultivars are sensitive to heat stress, with warm summers causing short life cycles, abortion of flowers and pods, which result in significant yield reduction. Yield loss can be minimized if we identify traits to maintain cooler canopy conditions under high air temperature. This experiment was carried out under field condition at two locations in Saskatchewan. Twenty-four genotypes represented various plant characteristics including canopy color, leaf type, canopy habit and flower color and were tested for canopy cooling traits. Results showed significant differences among genotypes in canopy temperature, canopy temperature depression, pigment and wax contents, spectral reflectance and vegetation indices including normalized vegetation index (NDVI), photochemical reflectance index (PRI) and water balance index (WBI).  Most traits were affected by plant characteristics. For example, peas with blueish canopy color gave higher chlorophyll content than red canopy pea. Pigment and wax concentration were negatively correlated with canopy temperature.  Genotypes with cooler canopy during high air temperature had lower percentage abortion. Pigments and wax enhanced canopy cooling through their protective role of high heat reflectance reducing radiation load.