Spectral reflectance indices reveal wheat variety response to heat and drought stress.

Developing crop varieties with stability to variable climates requires a challenging task of screening a large number of germplasm lines under diverse field conditions. To explore a fast, cost-effective, and non-destructive approach to phenotype bread wheat (Triticum aestivum L.) response to heat and drought stress, we used a spectroradiometer (325–1075 nm) for collecting whole canopy spectral reflectance indices (CSRI). Thirty bread wheat lines were seeded in replicated plots (1.2 x 3 m) at Agriculture and Agri-Food Canada’s research stations in Swift Current (SK) (low rainfall, high temperature), Indian Head (SK) (high rainfall, moderate temperature) and Lethbridge (AB) (early drought, moderate temperature). Spectral data was collected at grain filling stage for photochemical reflectance index (PRI), red normalized difference vegetation index (RNDVI), green normalized difference vegetation index (GNDVI), vegetation index (VI) simple ratio (SR), water index (WI), and two normalized water indices (NWI-1, NWI-2). Grain yield per plot ranged from 578 to 820 g at SC, 909 to 1296 g at IH, and 498 to 914 g at LB. At SC and LB that experienced drought like conditions in 2022, CSRI represented by NDVI, SR, VI and PRI were correlated highly and positively with grain yield whereas WI, NWI, and NWI2 showed negative correlation. Interestingly, the relationship for all these indices with grain yield was weak for Indian Head location that received excessive moisture throughout the growing season. The results demonstrated that CSRI can be used as a tool in germplasm selections for increased grain yield under heat and drought conditions.