Integrated aerial and destructive phenotyping differentiates chilling stress tolerance during early seedling growth in sorghum

Sorghum with greater chilling tolerance during early season has the potential to minimize terminal drought and heat stress damage and efficiently utilize early season residual moisture. Four promising chilling stress tolerant sorghum advanced breeding lines, a known early stage chilling tolerant Chinese landrace (Shan Qui Red - SQR) and a susceptible US elite cultivar (RTx430) as checks were assessed for chilling tolerance during emergence and early growth under field and controlled environments. Plants were exposed to a maximum day-time/minimum night-time temperature of 6/6°, 8/8°, 10/10°, 15/15°, 20/10°, 20/15° and 32/22 °C in two independent controlled environment growth chamber experiments. Field studies were conducted with two early (April 01 and 15) and regular (May 13 and June 02) plantings in 2016 and with one early (April 21) and regular (May 25) planting in 2017. Emergence rate and from seedlings harvested one month after emergence, leaf area, shoot weight, root weight, and other root morphological traits were recorded from all experiments. Aerial phenotyping using UAV fitted with multispectral camera was used to capture reflectance-based vegetation indices (NDVI and NDRE). Some advanced breeding lines recorded significantly better emergence, seedling growth and vigor, root biomass compared to SQR under chilling conditions. Aerial phenotyping indices from images taken between 30 and 60 days after emergence were consistently correlated with destructive measurements under early plantings, indicating their effectiveness in differentiating chilling responses. Aerial phenotyping indices have the potential to be utilized effectively for phenotyping genetically diverse populations for improving early season chilling tolerance in sorghum.