Quantifying the agronomic performance of new grain sorghum hybrids for enhanced early-stage chilling tolerance

Enhancing chilling tolerance to attain uniform emergence with better seedling vigor under temperatures <15 degrees C will enable earlier planting of sorghum. Early-stage chilling tolerant sorghum has the potential to better utilize residual soil moisture and enhance yield through extended vegetative and grain-filling periods. This study comprised of 12 genotypes, including four new hybrids developed from different parental combinations (two B-lines and three R-lines), parents and three checks (two inbred lines - RTx430 and SQR; and one commercial hybrid). The major objective of the study was to phenotype the above mentioned genotypes over two years under field conditions and in controlled environment chambers, to quantify the level of early-stage chilling tolerance and the impact of stress on yield related parameters and grain quality. An improvised phenotyping approach termed as "field-like" was devised for controlled environment chambers to replicate temperature conditions prevailing under field conditions. Systematic testing resulted in enhanced early-stage seedling vigor significantly correlating with constant chilling stress conditions compared to the improvised "field-like" treatment, strengthening the reliability of routinely followed constant chilling stress imposition under chamber conditions. Averaged across genotypes, early planting resulted in longer duration to flower and accumulated a higher number of growing degree units (GDU) during grain filling. Our most promising tannin-free hybrid (ARCH11192A/ARCH12012R) with enhanced chilling tolerance took 23 days (100 GDU) longer to reach flowering compared to regular planting, with the grain-filling period extended by three days (14 GDU). Reduction in grain protein and an increase in starch content with early planting indicated extended vegetative stage possibly providing additional carbon for the developing grains. In summary, developing tannin-free early-stage chilling tolerant hybrids can create opportunities to extend vegetative and grain-filling duration, paving the way to enhance grain sorghum productivity.