Diurnal Variations in Water Potential and Gas Exchanges in Two-Hybrid Oil Palms Under Water Deficit

Oil palm (Elaeis guineensis Jacq.) presents considerable sensitivity to water deficit and the identification of stress-tolerant hybrids is a strategy to improve the adaptation and growth of plants throughout the annual dry seasons. For this reason, we examined possible differences in water deficit tolerance in two oil palm hybrids (BRS Manicoré and BRS C 2501) subjected to moderate drought conditions. The comparison of hybrids was performed using diurnal curves of leaf water potential (Ψw), gas exchanges, and biochemical variables, such as chloroplast pigments and enzymes analysis. The experiment was carried out in a completely randomized design, in a 2 × 2 × 13 factorial scheme resulting from the combination of two hybrids versus two water regimes, and thirteen evaluation schedules. Regardless of the water regime, the maximum average value of net assimilation rates of CO2 (A), stomatal conductance to water vapor (gs), and water use efficiency (A/E) in both hybrids was registered at 8 h. Peaks of A, gs, and A/E coincided with milder climatic conditions during the morning. While decreases in these variables were observed with increases in air temperature and vapor pressure deficit between leaf and atmosphere throughout the day. The water deficit induced significant increases in the total carotenoids levels of BRS C 2501 (62%) and BRS Manicoré (220%), while chlorophyll a content was significantly reduced only in BRS C 2501 (36%) and chlorophyll b only in Manicoré (34%). It also mediated significant increases in the activities of glycolate and catalase oxidase in both hybrids; however, such increases were more expressive in BRS C 2501 than in BRS Manicoré. In conclusion, it can be inferred that BRS Manicoré presents more favorable physiological and biochemical responses to the water deficit imposed compared to BRS C 2501.