Tolerance to Drought and Water Stress Resistance Mechanism of Castor Bean

Castor bean (Ricinus communis L.) is a multipurpose crop; its oil has numerous applications worldwide and the last decade demonstrated a growing international demand. The aim of this work was to investigate the level of castor bean tolerance to drought and its possession of a water stress resistance mechanism by applying three different water regimes in a glasshouse pot experiment conducted for two years. The treatments applied were 70% (T₇₀-control), 55% (T₅₅) and 40% (T₄₀) of the available soil moisture. The results showed that the growth parameters height, trunk diameter, and fresh and dry weights of leaves and stems were not affected by the moderate water scarcity (T₅₅), while they were significantly decreased by T₄₀. Significant decrease in leaf number was observed in both T₅₅ (17%) and T₄₀ (27%) plants, with a delay of 4 weeks in the lower treated plants. Leaf area was decreased by 54% and 20% in T₅₅ and T₄₀ respectively, indicating that its reduction was mainly due to a reduction of leaf size than of leaf number. The leaf water potential was increased negatively with increasing stress, showing a water loss and decrease of turgidity in cells. Stomatal resistance was significantly higher at the higher water scarcity and this response indicates a water stress resistance mechanism. This result was also confirmed by the regression analysis performed between stomatal resistance and leaf water potential. In conclusion, castor bean showed a tolerance ability under water stress conditions and its early physiological reaction allows its acclimatization to drought conditions.