Effect of mycorhizal symbiosis, application of super absorbant gel, glycine-betain and sugar beet extract on physiological traits and seed yield of castor bean (Ricinus communis L.) in drought stress conditions

To study the effect of mychorizha, glysin betaein and sugar beet extract on some physiological and biochemical parameters of castor bean as a second crop under drought stress conditions, a split plot arrangement in randomized complete block design with three replications was carried out in the Agricultural Research Station of Oshnaviya, West Azarbijan, Iran, in 2012 and 2013. Drought stress applied at four levels (irrigation after soil moisture reached to 80%, 70%, 60% and 50% of field capacity) were as assigned to the main plots and foliar application with glycine betaine (50 mM), sugar beet extract (100%) and water (control) and the use of super absorbent gel A200 (225 kg.ha-1) and inoculation with mycorrhiza (Glomus mossea) were randomized in sub-plots. Foliar application of glycine betaine, sugar beet extract and water were carried out at leaf 10 stage of the plant, and mycorrhiza and super absorbent gel were applied at planting. Mean comparison showed that increasing stress intensity from 80% to 50% of field capacity decreased seed yield by 49%. The highest malondialdehyde content (177.2 nmol.gFW) was achieved in severe water deficit stress with spraying water (control). The highest seed yield (2730 kg.ha-1) and the highest activity of APX (117.9 A290.mg protein), CAT (87.1 A240.mg protein) and SOD (46.9 unit.mg protein) enzymes were achieved from foliar application of sugar beet extract. Therefore, at all levels of irrigation, glycine betain and sugar beet extract treatments through induction of tolerance mechanisims increased the activities of antioxidant enzymes and thus increased seed yield compared to control due to decreasing adverse effect of water deficit stress. Therefore, foliar spraying with sugar beet extract can be suggested to alleviate water deficit stress effect in castor bean.