Assessment of salt tolerance in rice cultivars in response to salinity problems in California

Stringent requirements for water holding for California rice producers who use pesticides have resulted in the loss of stand and visible symptoms of leaf damage for some growers. A field survey and subsequent series or experiments were conducted to determine the range or salt tolerance among 11 cultivars of rice (Oryza sativa L.) that are common to northern California rice-growing areas. A field assessment made on several farms led to the conclusion that growth reduction and stand loss were correlated with high salinity in soil mud and water. Plants from saline basins had significantly higher concentrations of leaf Na+ and Cl- than those from less saline basins. Greenhouse studies were conducted in sand cultures and flooded with saline waters having average electrical conductivities of approximately 1 (control), 3, 7, 11, 13, and 16 dS m-1. Salinity decreased emergence rates and final stand and led to reductions in shoot and root fresh and dry weights. At the highest salinity, shoot weights were 20% of the control after 17 d. Leaf tissues of plants grown at 16 dS m-1 had five times as much Na+ and three times as much Cl- as controls. Leaf concentration of K+ was decreased by about 40% by salinity, but tissue levels of Ca2+ and Mg2+ were unaffected. In a second experiment, salinity treatments were lowered to 0.8, 1.6, 3.2, 6, 8, and 10 dS m-1. There were significant differences in growth rates related to cultivar, but relative salt tolerance differences were negligible, leading to the conclusion that genetic differences among the rice cultivars are limited