The effectiveness of grafting to improve NaCl and CaCl2 tolerance in cucumber

Abstract

The aim of the current work was to determine whether grafting could improve salinity tolerance ofcucumber using three different salt stressors such as CaCl2, NaCl and their combination CaCl2+ NaClwith equimolar concentrations, and to study the changes induced by the rootstocks in the shoot growthat agronomical and physiological levels. A greenhouse experiment was carried out to determine yield,growth, fruit quality, SPAD values, electrolyte leakage, chlorophyll fluorescence, CAT, APX, GPX activitiesand mineral composition and assimilate partitioning of cucumber plants (Cucumis sativus L. cv. ‘Ekron’),either ungrafted or grafted onto two commercial rootstocks: ‘Affyne’ (C. sativus L.) and ‘P360 (Cucur-bita maxima Duch. × Cucurbita moschata Duch.) and cultured in quartziferous sand. Plants were suppliedwith four nutrient solutions: non-salt control, 20 mM CaCl2, 30 mM NaCl or 10 mM CaCl2+ 15 mM NaCl.Significant depression of yield, and shoot biomass production in response to an increase of salinity con-centration in the nutrient solution was observed with more detrimental effects with CaCl2. The three salttypes improved fruit quality in both grafting combinations by increasing fruit dry matter and total solublesolids content by 8% and 6%, respectively. The lowest SPAD index and the lowest efficiency of the PSII indark-adapted leaves, measured as the Fv/Fmratio were recorded in ungrafted plants treated with CaCl2.Moreover, at the three salt treatments the percentage of yield and biomass reduction in comparison tocontrol was significantly lower in the plants grafted onto ‘P360 and especially ‘Affyne’ than ungraftedplants, with the highest yield, and shoot reduction recorded with CaCl2in comparison to those recordedwith NaCl and CaCl2+ NaCl treatments. Grafted cucumber plants exposed to NaCl and CaCl2+ NaCl werecapable of maintaining higher chlorophyll content (SPAD index), higher photochemical activity of PSII,increased the capacity of antioxidant system by enhancing the GPX activity, a better nutritional status(higher N, K, and Ca, and lower Na) in the shoot tissues and a higher membrane selectivity in compar-ison with ungrafted ones. The higher crop performance of grafted (Ekron/Affyne) cucumber recordedwith NaCl than with CaCl2, was attributed to the limited capability of the rootstocks to restrict Cl−shootuptake, thus Cl−, which continues passing to the leaves, becomes the more significant toxic componentof the saline solution.