To understand the effects of salinity stress on four different growth stages of sorghum, a greenhouse experiment with 10 treatments, considering all possible combinations of salinity stress and salt- free periods was carried out. The four growth stages for stress application included: emergence until growing point differentiation, growing point differentiation until half bloom, half bloom until soft dough, and soft dough until physiological maturity. Treatments were arranged based on randomized complete block design with 3 replications at the Research Greenhouse of theFerdowsiUniversityofMashhadin 2010-2011. Salinity stress during early growth and panicle differentiation declined the plant height and tiller number. The highest biological yield was obtained from the control treatment, but it was the lowest when plants were salinized throughout the growing season. When plants were stress-free at 2-3 early stages and then subjected to salt stress, reductions in total dry matter were remarkably less than those experienced when salinity was imposed in later growth stages, especially if salinity occurred at a late individual stage. Continuation of salt stress from emergence to both blooming and soft dough stages led to remarkably adverse effects on grain yield. The effect of salinity appears to be most effective on yield components that are growing or developing at the time the salt stress is imposed. The critical period of salinity stress for biological yield was more distinct than that of the grain yield. This indicates that sorghum is not sensitive to salinity at seed setting and seed filling periods.

Keywords: Critical period of salinity stress control, Growth stage, Salt stress, Sorghum

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