Thanks to its multiple uses; its nutritional characteristics; and pleasing attributes related to touch, taste, smell or feel, tomatoes are the second most important vegetable crop after potatoes in the United States for area planted and total production (USDA, 2020). Being a warm-season crop, tomatoes are grown by Nevada farmers during the summer in open fields, gardens and in protected environments (e.g., hoop houses).
Growing vegetables in Nevada’s climate can be challenging because of high evapotranspiration levels resulting from high summer daytime temperatures and low air relative humidity. In addition, salts tend to accumulate in soils from low-quality irrigation water sources and over-fertilization, resulting in impaired vegetable production and yields.
Groundwater irrigation sources, in particular, can be high in salts in areas where geothermal waters and earthquake faults are common, such as in Nevada (Ayers & Westcot, 1985).
Soil electrical conductivity (EC) is a measure of the salts accumulated in soil (USDA, 1999) and affects the productivity of salt-sensitive crops when it is higher than 2.0 decisiemens per meter (dS m-1) (Shannon and Grieve, 1999). Most of Nevada’s soils are characterized by an EC that is above this threshold (i.e., between 2.3 and 9.3 dS m-1). High soil EC tends to increase concentrations of sodium and chloride in the soil even over other salinizing ions such as calcium, and sodium is especially toxic to many plants (Grattan and Grieve, 1999). Moreover, soil salinity lowers the soil water potential, making it more difficult for the plant to take up water and impairing the availability of other nutrients.
Tomatoes are considered to be moderately sensitive to salt stress, and in soils with EC greater than 2.5 dS m-1, tomato yields are estimated to decrease about 10% per each additional EC unit (Saranga et al., 1991). The effects of salt stress on tomato crops depend on the concentration of salts, duration of stress exposure, and developmental stage of the tomato plant. Because salt stress impairs many different metabolic processes of the plant, breeding new tomato cultivars for salt tolerance is challenging (Cuartero et al., 2006), and a salt tolerant tomato variety has not been developed yet.
Grafting is an agronomic technique where the root system of one plant is physically joined or grafted to the shoot of another plant, through a graft union or grafting point. The resulting grafted plant begins to grow and maintain the characteristics of the root system of the first plant and of the shoot of the second plant. Grafting tomato elite cultivars with tomato rootstocks could be an effective tool to facilitate tomato production under conditions of high salt concentrations (Singh et al., 2020). Root traits from rootstocks can enhance the productivity of an elite or desired cultivar by facilitating water and nutrient uptake under salt stress (Venema et al., 2008). Moreover, it has been shown that grafted tomatoes improve salt tolerance through the capacity of the rootstock to limit the transport to the shoot of toxic salts such as sodium and chloride (Estañ et al., 2005).
This Extension publication reports the results of University of Nevada, Reno Experiment Station research that tested six different commercial tomato rootstocks and one commercial tomato cultivar for salt tolerance under low, moderate and severe salinity levels. We analyzed biomass production and partitioning for each genotype and each salinity level.