Dhurrin Content Relates to Sorghum Seedling Growth in Marginal Soils.

Dhurrin content in leaves of mature sorghum plant is a quantitative measure of the level of pre-and postflowering drought tolerance. Postflowering drought tolerance in sorghum is linked to the staygreen trait which has been associated with decreased lodging, less susceptibility to charcoal rot, increased stem carbohydrates and improved grain yield under stress. Early enhanced screening of grain sorghum lines for high dhurrin levels will be an important component in breeding for improved post-flowering drought tolerance.

Sorghum genotypes of known dhurrin levels, determined from mature leaves were grown in four soil-irrigation combinations: potting soil Mix 1 plus nutrient irrigation (GM1), play sand plus nutrient irrigation (GM2), potting soil Mix 1 plus water irrigation (GM3), and play sand plus water irrigation (GM4). Fresh seedling weight (Fsw), seedling length (Fsl), dhurrin and sugars contents were determined at 5 and 10 days after emergence (DAE). Genotypes with high dhurrin (HD) levels show higher fresh seedling weights and lengths than low dhurrin (LD) levels genotypes only at 10 DAE, grown under play sand and water irrigation. Low dhurrin genotypes show significant negative correlations for seedling dhurrin content to Fsw and Fsl, and significant positive correlations of monosaccharide sugars to Fsw and Fsl, at 10 days after emergence under no nitrogen supply (sand and water). Genotypic variations in seedling Fsw and Fsl at 10DAE, grown under sand and water, showed similar trends (high to low) as known dhurrin levels of genotypes. No such variations were observed for dhurrin levels using either seedling dhurrin or sugar contents irrespective of soil-irrigation combinations and days after emergence. This study concludes that, at 10 days after emergence and under N-deficient soils, seedlings of sorghum genotypes with staygreen and thus postflowering drought tolerance potentials (high dhurrin levels) will outperform genotypes with senescence or pre-flowering drought tolerance potential (low dhurrin levels).