Physiological responses of castor ecotypes (Ricinus communis L.) to drought stress

Castor is normally cultivated in marginal lands, in arid and semiarid climates in which its oil is commonly used in industry and medicine. For investigation of physiological responses in different castor ecotypes under different water deficit conditions, the field experiment was conducted in two locations of Isfahan and Shahrekord in year 2013. The experiment was carried out in split plot arrangement in randomized complete block design (RCBD) with three replications, that included four drought stress levels of 30, 45, 60 and 75 percent moisture depletion in soil as main plot and six castor ecotypes of Esfahan, Ardesrtan, Arak, Naeen, Yazd and Ahvaz as subplot in two locations separately. The results from both experiments were analyzed by combined analysis. The measured traits included total biomass, total chlorophyll, stomata conductance, PAR absorbed by crop canopy (PAR1), absorbed radiation to total radiation and light extinction coefficient. The results showed that the highest chlorophyll is 128.6 SPAD in Yazd ecotype in Isfahan region under control and the lowest one is 25.8 SPAD in Yazd ecotype in Shahrekord under severe stress. The highest stomata conductance and light extinction coefficient are 647.5 Mmol/m2s in Ardestan and Yazd (1.03) in Shahrekord under control and the lowest ones are 53.5 Mmol/m2s in Ahvaz and 0.07 in Naein in Shahrekord region under severe stress. Under severe drought condition, absorption of photosynthetically active radiation decreased by plant canopy, stomata closed and total chlorophyll also reduced, therefore, photosynthesis rate reduced and biomass production significantly reduced compared to non-stress condition. Castor in Isfahan region produced higher biomass. While ecotypes, despite the differences in physiological responses, showed no difference in biomass.