Effect of post-flowering water stress on yield and physiological characters of grain sorghum genotypes. Mohammad Mostafa1, Maryam Shahbazi2*, Azim Khazaei3, Jahanfar Daneshian3, Soheil Naddafi2 and Hashem Pourirandoust2

Droughtis oneof the most importantfactors limitingcrop productioninarid and semiaridregions, such as Iran.In order to study drought stress in four grain sorghum varieties (Kimia, Sepideh, KGS15 and KGS23), an experiment was laid in randomized complete block design with three replications in a split plot arrangement. Water treatments were considered the main plot at three levels: irrigation after 60 mm evaporation as well-watered, normal irrigation till flowering and then irrigation after 120 mm evaporation (mild water stress), and water withholding after flowering (severe water stress). There were significant (P£0.05) decrease in grain yield, seed index, SPAD number and stomatal conductivity in post-flowering water stress, particularly in severe stress.Sepideh cultivar had the highest yield reduction of 73%, and KGS23 genotype had the least yield reduction of 29%, but still it was a good genotype if well-watered and the best in moisture stress conditions. Sepideh and KGS15 had a greatly significant reduction in stomatal conductivity of flag leaves in severe water stress and displayed premature leaf and stalk senescence. KGS23 as tolerant genotype with more elevated stomatal conductance under water stress probably had a more efficient water uptake by roots in comparison with the other genotypes.