Chloride and water stress effects on soybean in pot culture

Abstract

Abstract Chloride (Cl) toxicity in susceptible soybean (Glycine max (L.) Merr.) cultivars is caused by excessive uptake of Cl but the minimum concentration of soil Cl required to produce phytotoxicity is unknown. Also there is no evidence to indicate whether Cl toxicity can be induced in soybean cultivars designated as Cl tolerant under field conditions. Since the severity of the Cl problem appears to be accentuated by limited rainfall, there was a need to evaluate water stress effects with Cl rates on a susceptible cultivar. Potassium chloride solution was the source of Cl in each of three pot experiments using a Leefield sand (arenic Plinthaquic Paleudult). Experiment 1 evaluated treatments of 0, 91, 182, 364, and 728 mg Cl/kg of soil using a Cl susceptible cultivar. Experiment 2 compared treatment effects of 0, 300, and 600 mg Cl/kg of soil with four Cl susceptible and four Cl tolerant cultivars. In experiment 3, the effects of water stress treatments (none, medium, and high) and Cl treatments of 0, 100, 200, 300 and 400 mg/kg of soil were evaluated with a Cl susceptible cultivar. Increased amounts of applied Cl increased leaf scorch symptoms (Cl toxicity), shoot and seed Cl, and decreased shoot and seed weight of ‘Bragg’ soybean (experiment 1). The lowest rate of Cl (91 mg/kg) induced phytotoxicity. Concentrations of Cl in leaves, stems, and pods increased with increased Cl rate for both tolerant and susceptible cultivars, but levels were higher in susceptible cultivars (experiment 2). However, root Cl of tolerant cultivars was higher than that of susceptible cultivars where Cl was applied. Phytotoxicity was induced in susceptible and tolerant cultivars by 300 and 600 mg Cl/kg of soil, respectively. Water stress increased defoliation and decreased pod weight but had no significant effect on phytotoxicity or tissue Cl concentration of ‘Cobb’ soybean (experiment 3). Leaf scorch, defoliation, and concentrations of Cl in leaves, stems, and pods were increased and water usage and pod weight were decreased by increased Cl rate. Cl toxicity was induced by Cl application in cultivars previously designated as Cl tolerant under field conditions and root Cl was higher in tolerant than susceptible cultivars. Therefore, there remains a need to establish the range in soil Cl required to identify Cl tolerant and susceptible cultivars under greenhouse conditions and to study the mechanism for genetic control of Cl sensitivity in soybean cultivars.

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