Evaluation of the Effects of Zinc and Manganese Sulfate on the Improvement of Physiological Characteristics and Yield of Rapeseed Genotypes under Late-Season Drought Stress

In order to study the effects of late-season drought stress and foliar application of zinc sulfate (ZnSO4) and manganese sulfate (MnSO4) on physiological characteristics and yield of rapeseed cultivars, a factorial split-plot test has been conducted in a randomized complete blocks design for two cultivation years (2017-2019) in Karaj, Iran. The experimental treatments include two levels of irrigation (full irrigation (control) and withholding irrigation from flowering stage) and four levels of foliar application (control, ZnSO4, and MnSO4, separately, as well as their combined application) as factorial in the main plots, with rapeseed genotypes (Nima, Niloofar, and KS7) considered as subplots. Combined foliar application of zinc and manganese sulfate under full irrigation conditions increase the content of seed oil and soluble carbohydrates by 3% and 11%, respectively, compared to the control. On the other hand, withholding irrigation from flowering stage increases the percentage of seed oil and leaf proline content, compared to the control by 9% and 5.2%, respectively. Niloofar genotype has had the highest seed yield (5261 kg/ha) under full irrigation conditions, i.e. 9% and 11.8% higher than KS7 and Nima genotypes, respectively. Nima genotype with 3371 kg/ha has had the highest yield in the conditions of withholding irrigation. In general, in both irrigation treatments, simultaneous foliar application of zinc sulfate and manganese has had the greatest impact on the physiological traits of the studied genotypes, thus Niloofar genotype is recommended for full irrigation and Nima genotype for interrupted irrigation.