Cold Stress Resilience at Early Seedling in Sorghum Determined By Integrating Aerial Imagery and Destructive Phenotyping.

Four promising cold stress tolerant sorghum cultivars (ARCH10747-1, ARCH10747-2, ARCH12012 and ARCH12045), a known early stage cold tolerant check (SQR) and a susceptible US elite cultivar (RTx430) were accessed for their resilience to early stage cold stress under field and controlled environments. Plants were exposed to maximum day time/minimum night time temperature of 6/6°C, 8/8°C, 10/10°C, 15/15°C, 20/10°C, 20/15°C and 32/22°C in two separate control environment experiments. A field study was conducted with 2 regular control plantings (May 13 and June 2) and 2 early plantings (April 1 and April 15) to impose cold stress during early vegetative stage.

Seedlings were harvested one month after emergence and leaf area, shoot weight, root weight and other root morphological parameters using WINRHIZO were recorded as a measure of early seedling vigor. Seedling emergence rate and number were recorded. Grain yield and other yield components were also recorded from the field experiment. Aerial phenotyping using UAV (Unmanned Aerial Vehicle) fitted with RGB and multispectral cameras recorded reflectance based PSII activity, plant biomass and other growth parameters.

No difference was found among the genotypes in both field and controlled environment under normal temperature conditions and regular plantings. However, with cold stress exposure during early plantings in field and 15/15°C in controlled environment, ARCH cultivars recorded superior emergence, seedling growth and grain yield compared to popular cold-tolerant check (SQR). The results indicate presence of novel cold tolerant allele/s in these cultivars for minimizing early stage cold damage and exhibited potential to be integrated into ongoing breeding programs. Analysis of the aerial images collected at higher temporal frequency is currently ongoing and findings will also be discussed in the context of other field and growth chamber investigations.