Effect of Paclobutrazol on Canopy Temperature and Some Quantitative and Qualitative Characteristics of Two Rapeseed (Brassica napus L.) Cultivars in Different Irrigation Regimes

Plant growth regulators (PGRs) are used to prevent reduction in rapeseed grain yield under limited moisture conditions. A field experiment was conducted to investigate the effect of paclobutrazol (0, 50, 100, 150 and 200 mg L-1) on canopy surface temperature and some quantitative and qualitative characteristics of two rapeseed cultivars (Okapi and Natalie) under full irrigation and late season drought stress conditions at Research Station of College of Agriculture and Natural Resources of Payam Noor University of Fereydunshahr, Isfahan, Iran, in 2016-2017 growing season. The experimental design was split split plot based on randomized complete block design with three replicates. Results showed that all the treatments including late season drought stress, paclobutrazol and cultivar had significant effects on number of seeds per pod, pod length, seed weight, canopy temperature and seed yield. Both cultivars were highly sensitive to late season drought stress at flowering, so that drought stress led to a nearly 40% decrease in grain yield of both cultivars. In both cultivars the application of 100 mg L-1 paclobutrazol under full irrigation and 200 mg L-1 under late season drought stress produced the highest grain yield. Both cultivars had similar responses to drought stress and paclobutrazol, while Natalie (5346 kg ha-1) produced higher yield than Okapi cultivar (4910 kg ha-1). Also, in both cultivars the application of paclobutrazol reduced canopy temperature under drought stress conditions. According to our results, although drought stress suppresses rapeseed grain yield and yield components, the examined plant growth regulator could be harnessed to compensate, at least in part, for the yield suppression imposed by the late season drought stress. Therefore, use of paclobutrazol could be recommended to alleviate the drought stress effect on rapeseed.