Analyzing the effects of defoliation on physiological and biochemical characteristics of sunflower under cut irrigation.

Sensitivity to water deficit a few days before the heads emergence up to complete color change of grains is too much in sunflower. But the most sensitive stage to water deficit is at anthesis level. As a result, decrease in leaf area is the first reaction that a plant choose to adapt the storage of received water; this way is the most important mechanism of plant adaption to water deficit stress. In order to analyze the effects of defoliation on qualitative and quantitative characteristics of randomized complete blocks. The main plot was designed at four levels including the normal irrigation (S1), no irrigation from floret to flowering (S2), no irrigation from flowering to first stage o grain filling (S3), and no irrigation from first stages of grain filling to physiological maturity (S4). And the sub plot was designed at three level of on defoliation (F1), 25% defoliation (F2), and 50% defoliation. The results indicated that the main effect of no irrigation was significant an all factors under study including grain yield , biological yield , oil content, cytoplasm membrane resistance , Relative water content (RWC) , total chlorophyll, and proline. The main effect of defoliation was significant on all factors except for grain yield and biological yield. But, the interaction effect of no irrigation stress and defoliation was not significant on the factors under study. No irrigation at flowering to grain filling could decrease the grain yield to 44% comparing the normal irrigation. Also, under the same condition, the amount of proline increased significantly and reached 56.8 m mol / g; that is 49% more than normal irrigation condition. Moreover, 50% defoliation could increase the total chlorophyll and RWC significantly.