SALINITY TOLERANCE OF CITRUS ROOTSTOCKS - EFFECTS OF SALT ON ROOT AND LEAF MINERAL CONCENTRATIONS

The effects of three concentrations of sodium chloride (NaCl) on seven citrus rootstocks were studied under greenhouse conditions. Leaf and root mineral concentrations and seedling growth were measured. Sodium chloride was added to the nutrient solution to achieve final osmotic potentials of -0.10, -0.20, and -0.35 MPa. Increasing the concentration of NaCl in the nutrition solution reduced growth proportionally and altered leaf and root mineral concentrations of all rootstocks. Significant differences in leaf and root mineral concentration among rootstocks were also found under stressed and non-stressed conditions. Salinity caused the greatest growth reduction in Milam lemon and trifoliate orange and the least reduction in sour orange and Cleopatra mandarin. No specific nutrient deficiency was the sole factor reducing growth and causing injury to citrus rootstocks. Sodium chloride sensitivity of citrus rootstocks in terms of leaf burn symptoms and growth reduction could be attributed more to Cl than to Na. Sodium and Cl concentrations were greater in the leaves than in the roots, particularly at the medium and high salinity levels. Root Cl was not useful for assessing injury because no differences were found in root Cl concentrations among rootstocks. Increasing salinity level did not affect the level of N and Ca in the roots but did reduce N and Ca levels in the leaves. No relationship in mineral concentration or accumulation seemed to exist between citrus leaves and roots. At the -0.10 MPa salinity level, sour orange, rough lemon, and Milam were not able to exclude either Na or Cl from their leaves. Trifoliate orange and its two hybrids (Swingle citrumelo and Carrizo citrange) excluded Na at the lowest salt level used, but were unable to exclude Na at the higher salinity levels. Similarly, Cleopatra mandarin excluded Cl at the lowest salt level, but was not able to exclude Cl at higher salt concentrations. Hence, the ability of citrus rootstocks to exclude Na or Cl breaks down at higher salt concentrations.