Respostas fisiológicas de dois híbridos de palma de óleo ao déficit hídrico.

Abstract

Drought is one of the most important environmental stresse factor limiting conmiercial cultivation of oil palm in tropical areas. Therefore, the identification of drought tolerant hybrids of oil palm is an important strategy to enable the cultivation of the species in areas marked by low annual rainfall rates. This research was conducted in order to quantify the magmtude of changes in physiological variables (water potential and gas exchange), biochemical (antioxidant system and primary carbon metabolism) and morphological (biometrics and biomass) in two hybrid oil palm (BRS Manicoré and BRS C 2501) submitted to prolonged drought (leaf water potential around -4.0 MPa) and after resumption irrigation, inferring about its potential tolerance to drought. The overall effects of drought on gas exchange, concentrations of leaf carbohydrates, total soluble proteins and activities of enzymes associated with C02 fixation and starch and sucrose synthesis were more expressive in stressed plants ofBRS C 2501 than in BRS Manicoré. The BRS Manicoré presented more efficent antioxidant system to protect cells against oxidative stress to membrane lipids dmn BRS C 2501. The effects ofdrought on overall growíh did not differ among hybrids, however, it was noteworthy that BRS Manicoré grew more dense root system than BRS C 2501. Altogether, the BRS Manicoré presented a set of morpho-physiological and biochemical responses that should allow this hybrid tolerates drought more satisfactorily than BRS C 2501.

Drought is a major environmental consíraint limiting growth and yield of oii palm trees. In this study, two oil palm hybrids (BRS Marucoré and BRS C 2501) were grown in large coníainers and subjected ío a water déficit dunng 57 days. Leaf gas exchange analysis was combined with an in-depíh assessment ofthe antioxidant system over íhe drought imposition. Under drought, leaf water potential at predawn OPpd) decreased similarly in boíh hybrids. In parallel, there were decreases in the net CO2 assimilation rate (A), chlorophyil concentrations and Rubisco total acíivity. Overall, these decreases were more pronounced in BRS C 2501 than in BRS Manicoré. BRS C 2501 plants triggered more markedly its enzymatic antioxidant system earlier (^Fpd ~ -2.1 MPa) than did BRS Manicoré, but these responses were accompanied by Mgher concentrations of H2O2 and malondialdehyde in BRS C 2510 than in BRS Manicoré. With the progress of drought síress CFpd ~ -2.9 MPa and below), BRS Manicoré was better able ío cope with oxidative stress through a more robust antioxidant system. In addition, significant decreases in drought-induced NAD+-maiate dehydrogenase activities were only observed in stressed BRS C 2501 plants. Regardless of watering regimes, the total carotenoid, ascorbate and glutaíhione concentrations were higher in BRS Manicoré than in BRS C 2501. In conclusion, BRS Manicoré is better able to tolerate drought than BRS C 2501 by triggering multiple antioxidant strategies involved both in reactive oxygen species scavenging and dissipation of excess energy and/or reducing equivalents particularly under severe drought stress.