Water deficit and heat stress induced alterations in grain physico-chemical characteristics and micronutrient composition in field grown grain sorghum

The surge in sorghum-based foods as a gluten-free alternative for cereals like wheat, has directed sorghum research towards understanding and improving grain quality parameters. Since sorghum is usually grown in arid and semi-arid environments, is often prone to terminal water deficit and heat stress, inducing significant yield and quality losses. In environment 1, 24 genotypes assembled from diverse geographic locations, representing major sorghum growing regions of the world were grown in irrigated and dryland conditions. In environment 2, heat stress was imposed on the same 24 genotypes by placing custom-built field-based heat tents on already established plants, starting from booting until maturity. Water-deficit stress increased kernel hardness and total protein in grain, decreased protein digestibility, and micronutrient composition. Heat stress recorded lower total protein, protein digestibility, micronutrient composition and higher kernel hardness than control. irrespective of the stress, larger kernels recorded higher total protein, protein digestibility and micronutrient composition, but lower total starch and kernel hardness. Almost all the measured grain micronutrients (Zn, Fe, Mn and Cu) were reduced under both stresses compared to control. Genotypes such as SC372 and RTx7000 which maintained desired grain quality parameters under stress conditions can help in incorporating quality traits into sorghum improvement programs.