YIELD AND BLOSSOM-END ROT OF TOMATO AS AFFECTED BY SALINITY AND CATION ACTIVITY RATIOS IN THE ROOT-ZONE

Tomato plants were grown in rockwool slabs under glasshouse conditions at different salinities (3-9 mS cm(-1)) and times of the year to asse ss the possibilities for improving the taste of tomato fruit without r educing fruit quality in other respects. Various salts and combination s of salts (comprising Na, K, Ca, Mg, Cl, NO3-N, P and SO4-S) were app lied to increase the salinity in the root zone. Yield was reduced by i ncreased salinity due to reduced fruit size whereas the percentage fru it dry matter increased. Blossom-end rot was affected by the various n utrient elements applied to increase the salinity. The ion activity ra tios a(k)/root a(Ca)+a(Mg) and a(Mg)/a(Ca) in the root zone seem to be crucial and more important than the salinity for the development of b oth internal and external blossom-end rot. The higher the ion activity ratios, the higher is the risk of blossom-end rot. The incidence of i nternal blossom-end rot exceeded that of external blossom-end rot in s pring and autumn.