Effect of drought stress and defoliation on some of agronomical traits, yield and yield components of oil sunflower

In order to evaluation of effects of drought stress and defoliation stages and strata on yield and its components of Alstar hybrid of sunflower, an experiment was conducted during 006 - 007 at agricultural and natural resources research station of Khoy. Irrigation after 80, 0 and 60 mm evaporation from class A pan, as main factor, defoliation stage in two levels (R and R6 stages) as sub factor and defoliation location in three levels (control, middle up leaves defoliation and middle down leaves defoliation) as a sub sub factor were evaluated in strip split plot design in the basis of randomized complete block design in four replications. The results showed that drought stress decreased plant height, head diameter, harvest index, 000 seeds weight, full seeds number, seed yield and oil yield (except seed kernel percent), but increased huld seed percent. Seed yield was kg in irrigation after 80 mm evaporation treatment, but decreased in two other levels of irrigation up to 7 and 97 kg, respectively. Defoliation stage had significant effect on the studied traits and thousand seeds weight, seed yield and oil yield (except seed kernel percent) were higher in R6 stage. Comparison of the effect of defoliation in R6 and R stages on seed yield showed that leaves are important especially in primary reproductive growth stage. Defoliation in different parts of stem caused significant differences in plant height, head diameter, huld seed percent, harvest index, seed kernel percent, 000 seeds weight, full seed number, seed yield and oil yield and middle up leaves defoliation decreased most characters, significantly. Between interactions, middle down leaves defoliation in R6 stage didn’t have significant difference with control treatment. The results showed high value of sunflower upper leaves protection until beginning of seed filling stage.