Changes in Growth, Physiology, and Fatty Acid Profile of Rapeseed Cultivars Treated with Vermicompost Under Drought Stress

In recent years, the management of organic fertilizers and irrigation regimes has been the main topic in agricultural practices. The growth, physiological properties, and fatty acid composition of six rapeseed cultivars were assessed in a 2-year (2017–2018) field experiment using vermicompost (VC) under irrigation regimes in Karaj, Iran. Drought stress was imposed by stopping the irrigation at silique formation and flowering growth stages. The VC increased the plant height, silique number per plant, biomass, and grain yield. Drought stress at both silique formation and flowering stages decreased plant growth and yield, but increased proline concentration. Under well water condition, Zafar and Hyola4815 cultivars obtained the highest plant growth and grain yield, while RGS003 with the minimum changes in its morphological and physiological properties was identified as the most tolerant cultivar to drought stress. Zafar and Hyola4815 demonstrated the highest oil content and yield at well-watered conditions. GC/MC analysis showed that the main fatty acid composition of rapeseed cultivars was oleic acid (60.1–63.78%) followed by linoleic acid (13.94–17.73%), linolenic acid (3.85–6.67%), palmitic acid (3.71–5.18%), and ureic acid (0.15–0.23%). VC application increased palmitic acid and linoleic acid concentrations, but decreased linolenic acid content. The response of fatty acid profile to drought stress varied between the cultivars, in which the highest unsaturated fatty acid (UFA) was observed in Zafar under well-watered conditions. VC as an effective fertilizer and due to its high potential in improving soil properties and nutrient availability for plants would be advised to compensate for the decline in plant yield imposed by drought stress.