Response of four greenhouse pepper hybrids to NaCl salinity

The decline in availability of fresh water in the region of Ierapetra, Crete, Greece has resulted in the increased use of saline water for irrigation of greenhouse crops. The aim of this work is to study the responses of four greenhouse pepper hybrids, that are widely used in this region ( Capsicum annuum L., Drago, Sammy, Kappy and Gracia ), to NaCl salinity during in hydroponic culture ( perlite ) and culture in soil of young plants and during in vitro germination and seedling growth. Salinity treatments were imposed by adding NaCl either to the irrigation solution, or the substrate of the in vitro culture, at concentrations of 0, 12.5, 25, 50, 100, 150, 200 mM. High concentrations of NaCl affected the growth of the plants in hydroponic culture and in soil culture and the growth of seedlings in vitro in all four hybrids. Growth parameters such as height, number of leaves, fruits and flowers per plant and plant weight were significantly reduced in all hybrids. The percentage germination in the in vitro culture of the seeds was 100% for all hybrids on all NaCl concentrations. The photosynthetic rate (Po), the stomatal conductance, the intercellular CO2 concentration and the transpiration were significantly affected at high concentrations of NaCl in Drago and in Sammy. The Fv/Fm values of the leaves, which are related to the chlorophyll fluorescence, were significantly reduced at 100-200 mM NaCl, more in Kappy and Gracia and less in Drago and Kappy. The chlorophyll content in the leaves was negatively affected in all hybrids. NaCl caused a decrease in the soluble proteins in all hybrids. The decrease was significant in Drago, Kappy and Gracia in the greenhouse experiment while in vitro the protein content was less affected by the increasing concentrations of NaCl. Soil salinity positively affected the activity of GDH at 100 mM to 200 mM NaCl more in Kappy and Gracia and less in Sammy and Drago. In the vitro experiments there was a small increase in the higher concentrations of salt in all hybrids. The presence of NaCl affected the antioxidant enzyme GPX in Sammy Kappy and Gracia, SOD in Drago and POD in Kappy while APX was not affected. In general Sammy was the least affected by NaCl followed by Kappy , Drago, and Gracia.