Journal of Plant Process and Function

 In order to study the effects of bio fertilizers application on quantitative and qualitative yield, proline content and activity of some antioxidant enzymes in sunflower (Helianthus annus L.  var.  Urofelor) in different irrigation withholding levels, a factorial experiment was conducted based on randomized complete block design with three replications in research farm of faculty of Agriculture and Natural Resources, University of Mohaghegh Ardabili in 2015. Treatments were included bio fertilizer application in four levels [no bio fertilizer as control, Azotobacter chrocoocum strain 5, application of mycorrhiza (Glomus mosseae), Azotobacter chrocoocum+ Glomus mosseae] and three irrigation levels (full irrigation as control, irrigation withholding at 50% grain filling period; irrigation withholding at 50% flowering stage). Results showed that maximum efficiency of PSII photochemistry (F_v/F_m) (0.64) was obtained in full irrigation and both application of Azotobacter+Glomus. Comparison of means showed that maximum of proline content and antioxidant enzymes activity such as catalase, peroxidase, and polyphenol oxidase were obtained in irrigation withholding at 50% flowering stage and both application of Azotobacter+Glomus. Maximum of oil percentage (43.33 %) and chlorophyll content was obtained in full irrigation. Whereas, the highest soluble sugars was obtained under irrigation withholding at 50% flowering stage. Both application of bio fertilizer increased chlorophyll content, soluble sugars and oil percentage about 30.16%, 33.23% and 9.25% in comparison with control. Full irrigation increased chlorophyll content and oil percentage about 42% and 16.85% in comparison with irrigation withholding at 50% flowering stage. The highest of grain yield (2743.5 kg.ha^‑1) was obtained at application of Azotobacter+Glomus and full irrigation and the lowest of it (1696.5 5 kg.ha^‑1) was belonged to irrigation withholding at 50% flowering stage and no bio fertilizers. Under irrigation withholding condition at 50% flowering and grain filling period stages and without application of Azotobacter+Glomus decreased grain yield about 24.54 and 60% in comparison with full irrigation. Under irrigation withholding condition at 50% flowering and grain filling period stages, both application of Azotobacter+Glomus increased grain yield about 13.3 and 23.52%  respectively in comparison with control at the same irrigation withholding level. Based on the results, it seems that both application of Azotobacter+Glomus can be as a proper method for improving of grain yield of sunflower under water irrigation withholding condition.