The alkali spreading phenotype in Sorghum bicolor and its relationship to starch gelatinization

Sorghum, a staple food crop for millions of people in Africa and South Asia, is mainly consumed for the calorific value of its starch content, while the protein, mineral, lipid and fiber contents are important for flavour and nutritional quality. The starch structure largely controls cooking properties, processing quality, and digestibility. In this study, the Alkali Spreading Value (ASV) assay was modified to identify variants in sorghum starch quality. The modified ASV test was then used to identify sorghum genotypes with contrasting phenotypes for the trait. Sorghum EMS mutants with strong ASV phenotypes (ASV +) exhibited a range of starch gelatinization temperatures (GT) that were lower or higher than the wild-type Tx623 or Sepon82. Significant point biserial correlations were found between ASV and two starch-related traits: enthalpy (r = -0.53) and range of starch GT (T-c -T-o) (r = 0.60). ASV scores (ASV + in mutants vs ASV- in controls) correlated with lower enthalpies and greater starch GT ranges (T-c -T-o). These results suggest that the ASV mutants have mutations in genes involved in starch biosynthesis or processing that cause changes in starch GT.