Growth, Yield and Ion Relations of Strawberry in Response to Irrigation with Chloride-Dominated Waters

Strawberry is listed as the most salt sensitive fruit crop in comprehensive salt tolerance data bases.  Recently, concerns have arisen regarding declining quality of irrigation waters available to coastal strawberry growers in southern and central California.  Over time, the waters have become more saline, with increasing proportions of sodium (Na⁺) and chloride (Cl^-).   Due to the extreme Cl^- sensitivity of strawberry, the rising Cl^- levels in the waters are of particular importance.   In order to establish the Cl^- toxicity for strawberry, cultivars ‘Ventana’ and ‘Camarosa’ were grown in twenty-four outdoor sand tanks at the ARS-USDA U. S. Salinity Laboratory in Riverside, CA and irrigated with waters containing a complete nutrient solution plus Cl^- salts of Ca²⁺, Mg²⁺ and Na⁺.  The experiment was a randomized block design with two cultivars, six salinity treatments with osmotic potentials (OP) of  -0.0251, -0.0350, -0.0450, -0.0521, -0.0604, and -0.0800 MPa (electric conductivities  = 0.835, 1.05, 1.28, 1.48, 1.71, and 2.24 dS m^-1)  and four replications.  Fruit, leaf, petiole and root tissues were analyzed for mineral ion content. Marketable fruit yield of Ventana was not significantly reduced from a maximum of 925 g/plant until the osmotic potential of the irrigation waters fell below -0.06 MPa (1.70 dS m^-1) and solution Cl^- exceeded 8.2 mM.  Camarosa fruit yield under nonsaline conditions (770 g/plant) was lower than that of Ventana and yield was not significantly reduced until external OP fell below -0.052 MPa (1.48 dS m^-1) and solution Cl^- exceeded 6.1 mM.  Both cultivars appeared to possess an effective exclusion mechanism whereby Na⁺ was sequestered in the roots and Na⁺ transport to leaf, petiole and fruit tissue was limited.  Chloride content of the plant organs increased as OP decreased and substrate Cl^- increased from 0.1 to 13 mM.  Chloride content was highest in the roots, followed by the leaves, petioles and fruit.  Marginal leaf burn was associated with symptoms of Cl^- toxicity.  The data indicate that strawberry is sensitive to both osmotic and specific ion effects of salinity.