Temporal dynamics of thermal image-based canopy temperature estimates under drought condition in rice

Roots play important roles for maintaining crop productivity under drought. Root phenotyping under drought is difficult especially when dealing with large number of genotypes. Thus, a simple surrogate method such as the use of thermal image camera for estimating canopy temperature and leaf water status as a function of root plasticity under drought is being used for root phenotyping. The study was conducted to correlate thermal image based temperature analysis with root functions and leaf water status under drought; and identify the suitable time of the day to get thermal image that precisely detect canopy temperatures and leaf water status, and dry matter production under different soil moisture conditions. Rice genotypes IR64, YTH 183 and YTH 187 were grown and subjected to well-watered (WW) and drought (DR) conditions at 10% soil moisture content. Prior to the termination, the transpiration and canopy temperature estimates based on thermal image were measured from 8 AM to 4 PM at 2 hour interval. Under DR, the shoot dry matter production of IR64 was significantly reduced while those of YTH 183 and YTH 187 were not affected. The genotypic differences under DR were largely due to the differences in root branching ability as indicated by the maintained local lateral root lengths in both YTH 183 and YTH 187. The genotypic differences in transpiration rates were consistent only from 8 AM to 2 PM while it was substantially reduced at 4 PM. However, the genotypic differences in transpiration and thus shoot dry matter production can be precisely detected by canopy temperatures based from thermal image acquired between 10 AM to 2 PM only. This implied that estimation of canopy temperature using thermal image camera can precisely detect differences in leaf water status and thus dry matter production only when the image acquisition is done from 10 AM to 2 PM only.