Effects of Irrigation Deficit and Application of Some Growth Regulators on Defense Mechanisms of Canola

Abstract

A split-plot experiment arranged in a randomized complete blocks design with three replications was carried out in Safiabad Agricultural Research Center of Dezful in order to investigate the effects of foliar applications of ascorbic acid (AsA), salicylic acid (SA) and methanol (Me), under deficit irrigation conditions, in canola; there were 3 levels of irrigation as the main factor (irrigation after 70 mm evaporation from the pan as control, cessation of irrigation at the flowering stage and cessation of irrigation at the appearance of siliques) and 10 levels of foliar applications as sub-factor (100, 200 and 300 mg.l-1AsA; 100, 200 and 300 µM SA; 10, 20 and 30% (w/v) methanol; and foliar application of distilled water as control). Foliar applications were made during both budding and initiation of flowering stages. Results indicated that antioxidant enzymes showed different responses to deficit irrigation and foliar application treatments. Maximum catalase (CAT) and polyphenol oxidase (PPO) activities were observed under cessation of irrigation at flowering stage and foliar application of 300 µM SA, while ascorbate peroxidase (APX) reached its maximum activity under the same irrigation conditions and foliar application of 300 mg.l-1AsA. SA had more influence to increase in CAT and PPO activity under cessation of irrigation at flowering stage. The relative water content (RWC) was also decreased due to the drought stress caused by the cessation of irrigation. Foliar application of SA (100 μM) and Me (10% w/v) had more influence to maintain RWC compared to ascorbic acid under irrigation cessation at flowering stage.