Conclusion
Plants respond to drought stress through alteration in physiological and biochemical processes. Our results showed
that the activities of antioxidant enzymes increased under the WD in comparison to full-irrigated condition. However, the
activities of antioxidant enzymes were less in the extreme water deficit than the moderate water deficit. Moreover, the
water deficit reduced seed yield and some yield components. The advantage of high seed yield in Euroflor hybrid under
adequate water irrigation condition gave up when sunflower plants grown in water deficit condition. The sunflower
hybrids with less LAI were produced more seed yield when the sunflower plants endured water stress. The findings of
this research also showed that the GPX and CAT content can be used as a drought tolerance index to selection tolerant
genotypes under moderate and extreme water deficit conditions.
Acknowledgements
The authors are grateful to Dr. S. F. Saberali for some scientific assistance and statistical advisory.