Effect of NaCl in the irrigation water on growth, anti-oxidant enzyme activities, and nutrient uptake in five citrus rootstocks

Abstract

SummarySeven–month-old, uniform-sized seedlings of five citrus rootstocks [sour orange (Citrus aurantiam), Attani-2 (C. rugulosa), Troyer citrange (C. sinensis × Poncirus trifoliata), billikhichlli (C. reshni), and RLC-6 (C. jambhiri)] were irrigated to 70% of field capacity with water containing 0, 50, 100, or 200 mM NaCl for 180 d. Growth, in terms of plant heights and the numbers of leaves, decreased with increasing levels of salinity in all five rootstocks. The decrease in plant height was greatest in the salt-susceptible Troyer citrange and billikhichlli at higher levels of salinity. However, in the salt-tolerant sour orange and Attani-2, NaCl caused only a slight decrease in plant height. Defoliation was maximum in the salt-susceptible Troyer citrange and billikhichlli. The maximum increases in superoxide dismutase (SOD) and peroxidase (POD) activities were found in the salt-susceptible Troyer citrange at higher levels of salinity. Leaf proline contents increased most in Attani-2, sour orange, and RLC-6 at higher levels of salinity.The concentration of Na+ ions in leaf tissues increased to a maximum in Attani-2; while, in root tissues, RLC-6 and Troyer had the highest Na+ ion contents. The maximum increase in leaf Cl– ion levels occurred in Troyer citrange, and the minimum was in RLC-6, at 200 mM NaCl. These data suggest that higher levels of proline accumulation and leaf abscission could be used as indicators for screening citrus rootstocks for resistance to NaCl stress. Sour orange and Attani-2 were able to exclude Cl– ions, whereas Troyer citrange appeared to exclude Na+ ions at lower levels of NaCl. Further studies are required to observe the translocation of harmful and beneficial mineral elements to scion cultivars grafted onto sour orange and Attani-2 and grown under NaCl stress. Overall, salt-tolerance increased in the following order: Troyer ì billikhichlli ì RLC-6 ì Attani-2 ì sour orange.