Interstocked Verna Lemon Trees Improves the Salt Tolerance by Reducing Leaf Cl-Concentration

摘要

Salinity is a worldwide problem in citrus due mainly to the leaf chloride accumulation and toxicity. The aim of this work is to increase citrus salt tolerance by using interstocked trees. Three combinations of two year old Verna lemon trees (Citrus Union L.)were used in these experiments: Vema lemon grafted on Sour orange (C. aurantium L. ; Verna/SO) , Vema lemon grafted on SO interstocked with Valencia orange (Citrus sinensis Osb; Verna/V/SO) and Verna lemon on SO interstocked with Castellano orange (Citrus sinensis Osb; Verna/C/SO ). Trees were grown under greenhouse condition and supplied with nutrient solution containing either 0 (control) , 30mmol/L NaCl or 60mmol/L NaCl. After twelve weeks of salt treatment, growth parameters, leaf mineral concentration, leaf water relation and leaf gas exchange were determined. Based on the smallest salinity-induced leaf growth reductions, interstocked trees had higher salinity tolerance than Verna/SO. In addition, comparing both interstocked combination trees, Verna/V/SO and Verna/C/SO, it was observed that leaf growth reduction by salt treatment was less in ' Valenciano' than in 'Castellano' orange. Leaf Cl" and Na+ concentration was higher in Verna/SO than Verna/C/SO and Verna/V/SO, suggesting that interstock in citrus trees could limit the root Cl - uptake and/or transport to the shoot. Salinity reduced leaf water potential and osmotic potential such that leaf turgor was increased in all three Verna combination trees. The gas exchange parameters, net assimilation of CO2 and stomatal conductance, were reduced in salinized Verna trees relative to trees from control treatment, but there were significant differences among trees on SO, V/SO and C/SO, but there were significant differences among trees on SO, V/SO and C/SO.