Methods to Assess Potential Chloride Stress in Citrus: Analysis of Leaves, Fruit, Stem-xylem Sap, and Roots

Chloride stress in commercial citrus is predominantly a result of increased osmotic pressure in the plant as a result of excess chloride. The source of the chloride is usually from the soil solution, where it is absorbed by the roots. After being absorbed, chloride flows through the xylem in the transpiration stream to the shoot, where it is accumulated by transpiring tissues such as leaves and fruit. Monitoring chloride concentration along any of these steps can be used to assess potential stress in the tree. Since some of these tissues tend to accumulate chloride (fruit and leaves) while others do not (root and xylem), analyses should be interpreted within the context of these differences. Having high chloride concentration in roots or xylem-water at a specific sampling time does not necessarily mean that leaves have already accumulated chloride to a toxic level, while having high chloride concentration in fruit or leaf analysis does not necessarily mean that the trees are still being exposed to high salinity in the soil solution. The advantages of the various analyses, as well as their difficulties, are discussed. It was concluded that a combination of xylem sap chloride analysis and leaf chloride analysis are the most useful tools for assessing potential chloride stress in citrus trees.