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 sal inity on the water relations, osmotic adjustment and growth of melon p lants (Cucumis melo, L.). Three saline treatments (20, 40 and 60 mM Na Cl corresponding to 4, 6 and 8 dS m(-1), respectively) were applied at four different phenological stages (seedling, flowering, fruit set an d fruit growth) to compare the effect of the time of application on th e parameters studied. A reduction in stomatal conductance, water poten tial and osmotic potential was observed with all treatments. The degre e of osmotic adjustment observed indicated that no changes in leaf tur gor occurred after any of the saline treatments applied at the differe nt stages. Total sugar concentration increased in the leaves immediate ly after all treatment applications but later reverted to control valu es. No changes were observed in the total amino acid concentration. Si milar and significant increases were observed in leaf Cl- and Na+ conc entrations, which were greater at higher NaCl concentrations. Analysis of the contribution by the different solutes showed that inorganic co mpounds were increased to a greater extent than organic compounds afte r treatment application. Measurements of shoot height and leaf elongat ion rate showed that only salt applications during fruit set produce s light reductions in these two parameters while greater alterations wer e observed with the rest of the treatments. (C) 1998 Published by Else vier Science Ireland Ltd. All rights reserved.