Time course of solute accumulation and water relations in muskmelon plants exposed to salt during different growth stages

A greenhouse experiment was carried out to determine the effect of salinity on the water relations, osmotic adjustment and growth of melon plants (Cucumis melo, L.). Three saline treatments (20, 40 and 60 mM NaCl corresponding to 4, 6 and 8 dS m(-1), respectively) were applied at four different phenological stages (seedling, flowering, fruit set and fruit growth) to compare the effect of the time of application on the parameters studied. A reduction in stomatal conductance, water potential and osmotic potential was observed with all treatments. The degree of osmotic adjustment observed indicated that no changes in leaf turgor occurred after any of the saline treatments applied at the different stages. Total sugar concentration increased in the leaves immediately after all treatment applications but later reverted to control values. No changes were observed in the total amino acid concentration. Similar and significant increases were observed in leaf Cl- and Na+ concentrations, which were greater at higher NaCl concentrations. Analysis of the contribution by the different solutes showed that inorganic compounds were increased to a greater extent than organic compounds after treatment application. Measurements of shoot height and leaf elongation rate showed that only salt applications during fruit set produce slight reductions in these two parameters while greater alterations were observed with the rest of the treatments. (C) 1998 Published by Elsevier Science Ireland Ltd. All rights reserved.