Evaluation of changes in the water relations, osmotic adjustment and stay- green of different genotypes of sorghum under post-flowering drought stress

To investigate the effects of drought stress on the water stress, osmotic adjustment and stay green of sorghum genotypes and their relationship with grain yield, a split-plot on randomized complete block design with three replications was conducted at the experimental field of Seed and Plant Improvement Institute, Karaj, Iran in 2015. The main factor was three treatments: control (irrigation after 60 mm evaporation from the surface evaporation pan), mild stress (routine irrigation until 50% flowering stage followed by irrigation after 120 mm evaporation from surface evaporation pan). Extreme stress (routine irrigation until 50% flowering stage and water holding after it) and five sorghum genotypes (Kimia, Sepideh, KGS15, KGS23 and KGS32) were considered as sub-plots. Samples were taken at 14, 21 and 28 days after 50% flowering stage. The results showed that drought stress significantly reduced leaf relative water content and increased canopy temperature in all genotypes and significantly increased osmotic adjustment in most genotypes under severe drought stress. Kimia and KGS23 genotypes were identified as the most tolerant genotypes based on the of grain yield, drought tolerance index, leaf relative water content and osmotic adjustment. Additionally, KGS23 genotype with the highest chlorophyll content as a stay green phenotype is suggested to cope with drought stress. There was a positive significant correlation between grain yield and leaf relative water content, weight of the thousand grains, chlorophyll content and negative and significant correlation with canopy temperature. The results of this study showed that in addition to the importance of water relations and osmotic adjustment, stay green is one of the most important process related to yield in terminal drought stress in drought tolerant genotypes of sorghum.