Grafting cucumber plants enhance tolerance to sodium chloride and sulfate salinization

Abstract

The aim of the current work was to determine whether grafting could improve salinity tolerance of cucumber using two different salt stressors such as NaCl and Na2SO4 with equimolar concentrations, and to study the changes induced by the rootstock in the shoot growth at agronomical and physiological levels. A greenhouse experiment was carried out to determine yield, growth, fruit quality, leaf gas exchange, electrolyte leakage, SPAD, and mineral composition and assimilate partitioning of cucumber plants (Cucumis sativus L. cv. ‘Akito’), either ungrafted or grafted onto the commercial rootstock ‘PS1313’ (Cucurbita maxima Duch.×Cucurbita moschata Duch.) and cultured in quartziferous sand. Plants were supplied with three nutrient solutions: non-salt control, 27mM Na2SO4, or 40mM NaCl. Significant depression of yield, shoot and root biomass production in response to an increase of salinity concentration in the nutrient solution was observed with more detrimental effects with NaCl treatment. The two salt treatments, especially NaCl, inhibited photosynthesis, pigment synthesis, and membrane integrity. Salinity with NaCl and Na2SO4 improved fruit quality in both grafting combinations by increasing fruit dry matter and total soluble solids content. Moreover, at the two salt treatments the percentage of yield and biomass reduction in comparison to control was significantly lower in the plants grafted onto ‘PS1313’ than ungrafted plants, with the highest yield, shoot and root reduction recorded with NaCl in comparison to those recorded with Na2SO4 treatment. Grafted cucumber plants exposed to Na2SO4 were capable of maintaining higher net assimilation rates, higher chlorophyll content (SPAD index), a better nutritional status (higher K, Ca and Mg and lower Na) in the shoot tissues and higher membrane selectivity in comparison with ungrafted ones. The higher crop performance of grafted cucumber recorded with Na2SO4 than with NaCl, was attributed to the inability of the rootstock to restrict Cl− shoot uptake, thus Cl−, which continues passing to the leaves, becomes the more significant toxic component of the saline solution.