Effect of drought stress and foliar application of growth regulators on photosynthetic pigments and seed yield of rapeseed (Brassica napus L. cv. Hyola 401)

Changes in environmental conditions have led to various types of stresses that affect plants growth, development, and also its survival. Since the growth regulators improve plant tolerance to unfavorable environmental conditions, therefore, y the effect of drought stress and foliar application of some growth regulatorson rapeseed cv. Hyola 401 was studied. A field experiment was carried out as split plot arrangements using randomized complete block design with three replications at Safiabad Agricultural Research Center, Dezful, Iran during 2012-2014. The main plots were assigned to three irrigation levels; irrigation after 70mm evaporation from evaporation pan as control treatment (Optimum irrigation), withholding irrigation at flowering and silique stages, and sub plots included 10 levels of foliar application (100, 200, 300 mg.l-1 ascorbic acid, 100, 200, 300 μmol; salisylic acid; 10, 20, 30 vol% methanol and distilled water as control treatment). Results showed that withholding irrigation at flowering and silique stages led to reduction in grain yield by 38% and 15%, respectively. The interaction of withholding irrigation × foliar application showed that the highest (4493 kg.ha-1) seed yield under optimum irrigation conditions belonged to foliar application of ascorbic acid (300 mg.l-1) and the lowest (1968 kg.ha-1) to withholding irrigation at flowering stage and foliar application of distilled water (control). Foliar application of ascorbic acid (300 mg.l-1) led to enhancement of seed yield under optimum irrigation conditions and withholding irrigation during the silique stage. By increasing drought stress severity chlorophylla decreased while chlorophyllb was enhanced. Effect of methanol (30%) on proline accumulation was more than ascorbic acid and salicylic acid under mild and severe drought stress conditions. It was concluded that application of growth regulators increased seed yield due to increase in proline and phytosynthetic pigments accumulation and their effect on seed yield components. Application of ascorbic acid (300 mg.l-1) under optimum irrigation and mild stress and methanol (30%) at severe stress conditions improved seed yield of rapeseed cv. Hayola 304.