Canopy temperature depression (CTD) and canopy greenness associated with variation in seed yield of soybean genotypes grown in semi-arid environment

Method to measure canopy temperature depression (CTD) by employing thermal imaging system for crops like soybean, which is sensitive to low soil moisture has not been standardised/optimised. Hence, the present study was conducted to optimise the thermal imaging method and evaluated the CTD along with canopy greenness-based physiological traits in screening/selecting soybean genotypes suitable for semi-arid environment. The CTD and canopy greenness were measured six to eight times during different growth phases/stages using infrared (IR) and visible cameras mounted on a semi-automatic trolley that allowed rapid acquisition of high quality thermal and visible images, respectively. The CTD measured at the reproductive stage explained a major proportion of the variation in grain yield under both well-watered and water-stressed conditions. This could be attributed to close association between plant's capacity to keep its canopy cooler (low canopy temperature) and canopy greenness (higher chlorophyll content) as indicated by efficient photosynthesis which leads to grain yield. These results indicated that in addition to assess stay green features, CTD along with canopy greenness can also be used as a key trait of leaves in the selection of soybean genotypes for higher adaptability to low soil moisture stress conditions, a common feature exists under semi-arid regions.