Physiological and biochemical responses and fruit production of noni (Morinda citrifolia L.) plants irrigated with brackish water

Searching for plants that are more tolerant to salinity for commercial purposes is necessary for cultivation in soils that are saline and/or irrigated with brackish water. Thus, this study aimed to evaluate the effects of irrigation water salinity on soil salinization, and some physiological and biochemical parameters in noni plants, aiming at a better understanding of the mechanisms of salt tolerance in this species. The experiment was conducted in a completely randomized design with 5 replicates. Noni plants (Morinda citrifolia L.) were grown in pots containing 20 kg of soil and irrigated using different levels of electrical conductivity of the water (ECw): 0.3; 2; 4; 6 or 8 dS m(-1), adopting a leaching fraction of 0.10. Electrical conductivities of soil saturation extract and drainage water, plant growth, production, gas exchange, relative water content, absolute integrity percentage of cell membrane, chlorophyll a fluorescence, pigments, and accumulation of solutes were evaluated in two different periods (60 and 210 days after treatment (DAT)). The leaching fraction used (0.10) was not enough to prevent soil salinization with increase of ECw. The increase of ECw reduces CO2 assimilation due to stomatal (60 and 210 DAT) and non-stomatal (210 DAT) limitations compromising the growth of noni plants. The increase of Na+ and Cl- contents induced by the increase of ECw causes disturbances in the ion homeostasis and reduces the membrane integrity. However, together with the accumulation of solutes contribute to the maintenance of the water status of noni plants under saline conditions.