The effect of specific ion toxicity during salt stress was tested in the pr
esent study. The experiment was repeated twice, in 1996 and 1998, with 'Nem
aguard' peach seedlings and rooted cuttings grown in hydroponics under two
NaCl concentrations (50 and 30 mM). Foliage was Separated in symptomatic an
d symptomless leaves and the amount Of sodium (Na+) and chloride (Cl-) was
determined. Significantly higher Na+ content was found in symptomatic than
in symptomless leaves in both experiments, whereas in only two of the six e
ases was Cl- content higher in symptomatic than in symptomless leaves. The
Na+ threshold for leaf scorch was somewhere between 4 and 6 mg.g(-1) dry we
ight. Results indicated that Na+ accumulation, rather than Cl- accumulation
, was associated with the familiar marginal and interveinal scorch symptoms
seen in salt-stressed, peach leaves.