D. Neocleous - Agricultural Research Institute, Ministry of Agriculture, Natural Resources and Environment, P. O. Box: ۲۲۰۱۶, ۱۵۱۶ Nicosia, Cyprus.
A. Koukounaras - Department of Horticulture, Faculty of Agriculture, Aristotle University, Thessaloniki, Greece.
A. S. Siomos - Faculty of Agriculture, Aristotle University of Thessaloniki
M. Vasilakakis - Department of Horticulture, Faculty of Agriculture, Aristotle University, Thessaloniki, Greece.

The objective of this work was to study the responses of two baby lettuce (Lactuca sativa L.) cultivars, namely, green Paris Island and red Sanguine, to different NaCl concentrations (۰, ۵, ۱۰, and ۲۰ mM). The study was conducted in a floating system and plants were harvested at the stage of ۵-۶ leaves, outside leaf ۶-۱۰ cm in length (۲۵ and ۳۱ days after sowing for green and red lettuce, respectively). Photosynthetic parameters (photosynthesis rate, stomatal conductance, transpiration rate, and intercellular CO۲ concentration) and yield (leaf fresh weight) as well as color [L* (lightness), C* (saturation), Hº (object’s color)], pigments (Chla, Chlb, total chlorophyll, carotenoids and anthocyanins) and quality indices (appearance, freshness, taste and texture) were determined. The results indicated that, in both cultivars, leaf fresh weight was reduced at ۲۰ mM NaCl; the reduction depended on the limited water accessibility and photosynthetic rate was suppressed in high salt concentration through stomatal limitations aiming at the retention of water but resulting in restricted availability of CO۲. Nevertheless, no limitations were observed in photosynthetic pigments and, thus, stomatal closure was the dominant factor limiting photosynthesis. On the other hand, salinity improved anthocyanin content and coloration in red lettuce and enhanced freshness in green lettuce.

Gas exchange, Leafy vegetables, NaCl, Plant growth, Sensory quality