Variable salinity responses and comparative gene expression in woodland strawberry genotypes

Commercial strawberry cultivars are sensitive to salinity. These plants are octoploid (2n = 8x = 56) making analysis of complex traits such as salt tolerance difficult. Hence, the objective of this study was to evaluate eight woodland diploid strawberry genotypes for their physiological and genetic responses under high salinity conditions. Shoot salt tolerance (ST) index of eight genotypes irrigated with water of electrical conductivity (ECiw) of 8 dS m(-1) ranged from 0.41 to 0.86. Average Cl concentration in leaves was more than 11-fold higher than Na concentration, indicating that Cl- toxicity is more critical than Na+ for diploid strawberries. Improved water use efficiency (WUE) due to reduced stomatal conductance (gs), intercellular CO2 concentration (Ci), and transpiration rate (Tr) was associated with improved ST index. Expression analyses of eleven genes involved in Na+ and Cl- transport revealed differences in component traits responsible for salt tolerance. Increased expressions of SOS2, NHX1 and NHX2 in salt-tolerant genotypes suggest that Na+ sequestration in vacuoles may play an important role in salt tolerance in strawberry. Additionally, a chloride channel gene (CLC_C) was shown to be critical for salt tolerance. Understanding the genetic mechanisms regulating salt tolerance will be critical in developing strawberry germplasm more tolerant to salinity.