Study on the salinity tolerance in Citrus latifolia (Yu. Tanaka) Tanaka

Abstract

Saltwater intrusion in the Mekong Delt, an urgent problem, affected the growth of fruit trees in general and Citrus latifolia (Yu. Tanaka) Tanaka in particular. Sodium chloride in saline soils cause the water stress on plant roots leading to the leaf senescence and death of plant. Therefore, in this study, the salinity tolerance of the studied plant was investigated under conditions of additional sodium chloride in soil at various concentrations (from 0 to 16 g/L) to determine the salinity tolerance threshold of the plants, and then the roots were water irrigated and the leaves were sprayed by KNO3 solution at concentrations from 0 to 10 g /L to improve the salinity tolerance. The results showed that after 2 weeks of treatment of sodium chloride 4‒16 g/L, the increased saline caused the osmotic stress, increased the defoliation but reduced the leaf renewal, the fresh weight, the chlorophyll index, the Citrus latifolia growth, and decreased the aperture size and the photosynthetic intensity over time. The salinity stress promoted the ligninization in the rhizosphere parenchyma cells, reduced the root renewal and elongation. In addition, treatments for the plant recovery were also carried out by irrigating at the roots and spraying KNO3 10 g/L solution on the leaves. After 3 and 6 weeks, irrigation treatments could only recover plants from sodium chloride at 4‒8 g/L, indicating by the new leaf formation, the maintenance of the chlorophyll content in leaves and the decrease of the proline content. Sodium chloride solutions of 12 and 16 g/L caused a complete death of plants which could not be recovered after 6 weeks of watering. The treatment of sodium chloride combining with KNO3 10 g/L spray helped the aperture opening and increasing the proline accumulation in leaves and roots. In addition, role of endogenous plant growth regulators was also discussed to clarify physiological changes in saline stress conditions.