A field research was carried out in the years of 2005, 2006 and 2007 in order to determine the effect of irrigation and water stress imposed at different growth stages on quantity and quality traits of Virginia tobacco plants. A randomized complete block design with four treatments and three replications was applied at the Rasht tobacco research station. Treatments were: no irrigation (dryland farming) as the complete water stress (WS<sub>0</sub>), water stress till the end of flower bud forming stage (WS<sub>1</sub>), water stress till the end of flowering stage (WS<sub>2</sub>) and full irrigation (WS<sub>3</sub>) as control in each cropping season. The combined analysis of variance showed that the effect of water stress on all the traits related to yield, quality traits and all the traits related to yield components except number of leaves, was significant (<i>P</i> < 0.01). The interaction between year and water stress showed that the treatment of WS0 in all three experimental years significantly (<i>P</i> < 0.05) affected the fresh and dry leaf yield, plant height and sugar and nicotine percentage. The comparison of means of three years (average of three years) also revealed that the treatment of WS<sub>0</sub> significantly (<i>P</i> < 0.05) affected all of the traits which were related to tobacco quantity and quality except for the number of leaves. Moreover, the level of water productivity in recognition of each water volume unit for three experimental years for the treatments of WS<sub>1</sub>, WS<sub>2</sub> and WS<sub>3</sub> were 1.223, 0.873 and 0.594 kg/m<sup>3</sup>, respectively, in the case of average dry leaf yield. Consequently, the results indicate that with optimizing irrigation application we can reach the higher level of productivity.
Effect of water stress at different growth stages on quantity and quality traits of Virginia (flue-cured) tobacco type