Variable salinity responses and comparative gene expression in woodland strawberry genotypes

Authors: Sandhu, Devinder; Pudussery, Manju; Ferreira, Jorge; Liu, Xuan; PALLETE, ANDREW - University Of California; GROVER, KULBHUSHAN - New Mexico State University; Hummer, Kim

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2019
Publication Date: 5/7/2019
Citation: Sandhu, D., Pudussery, M.V., Ferreira, J.F., Liu, X., Pallete, A., Grover, K.K., Hummer, K.E. 2019. Variable salinity responses and comparative gene expression in woodland strawberry genotypes. Scientia Horticulturae. 254:61-69. https://doi.org/10.1016/j.scienta.2019.04.071.
DOI: https://doi.org/10.1016/j.scienta.2019.04.071

Interpretive Summary: The US is the second largest producer of strawberries in the world, after China, and California is the main producing state. As strawberries are sensitive to salinity, fruit yield decreases significantly even with small increases in salinity of the soil or the irrigation water. Commercial strawberry cultivars have 8 sets of chromosomes and 4 subgenomes, so analyzing complex traits, such as salt tolerance, is more challenging than starting with diploid strawberries. Hence, our objective was to evaluate eight woodland diploid strawberry genotypes for their physiological and genetic responses under salinity. 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 content in leaves was more than 11-fold higher than Na content, indicating that Cl-, more so than Na+, is likely to be a toxic ion for diploid strawberries. Improved water use efficiency (WUE) was associated to reduced stomatal conductance (gi), intercellular CO2 concentration (Ci), transpiration rate (Tr), and also with improved ST index. Expression analyses of eleven genes involved in Na+ and Cl- transport revealed important differences in component traits responsible for salt tolerance and helped identify the most salt-tolerant genotypes. Increased expressions of the genes SOS2, NHX1, and NHX2 in salt-tolerant genotypes suggest that Na+ sequestration into vacuoles may play an important role in salt tolerance in strawberry. Additionally, a gene (CLC_C) that transports Cl in or out of cells was shown to be critical for salt tolerance. Our data increases the understanding of the genetic mechanisms regulating salt tolerance in strawberry plants and could be applied to the cultivated polyploid strawberry. Our results will help strawberry breeders and geneticists to develop new salt-tolerant commercial cultivars, which in turn will allow farmers to increase crop yield in marginal lands, and to use cheaper recycled waters.

Technical Abstract: 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 dSm-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.