EFFECTS OF NACL ON GROWTH AND PHYSIOLOGY OF SOUR ORANGE AND CLEOPATRA MANDARINE SEEDLINGS

The responses of sour orange (SO) and Cleopatra mandarin (CM) to salt stress were studied because of the difference in their ability to accumulate Cl in the leaves. Seedlings of these two citrus rootstocks were grown in fine sand under greenhouse conditions. Salinity treatments were initiated by adding NaCl to half-strength Hoagland's solution to achieve final osmotic potentials of -0.10, -0.20, and -0.35 MPa. The no-salt control treatment had an osmotic potential of -0.05 MPa. Seedlings were harvested 6 months after starting NaCl treatments. No significant differences in growth, root hydraulic conductivity (RC), stomatal conductance, and evapotranspiration were detected between SO and CM. However, all these variables were significantly reduced by NaCl. At a relatively low salinity level (-0.10 MPa), shoot and root dry weights, stem cross-sectional area, total leaf area, and fibrous root length were reduced by 44-55%. With all treatments, a positive linear relationship was found between RC and stomatal conductance. Significant differences between SO and CM were found in leaf succulence, specific leaf weight (SLW), Cl accumulation, and leaf chlorophyll content. Sour orange seedlings accumulated higher amounts of Cl and had higher SLW and succulence but lower chlorophyll than CM seedlings. At the first salinity level, chlorophyll was reduced by 56% in SO but only by 11% in CM. The different responses to salt stress between the two rootstocks were mainly attributed to the known failure of SO to exclude Cl even at relatively low salinity levels.