Sensitivity of soft red winter wheat cultivars to chlorate-induced toxicity

The use of chlorate as a nitrate analogue to screen soft red winter wheat (Triticum aestivum L.) cultivars for differences in nitrate reductase activity (NRA) was studied by adding potassium chlorate to a hydroponic nutrient solution in which wheat seedlings were growing. After 14 days, leaf symptoms indicating chlorate-induced toxicity were rated. It was hypothesized that wheat plants which were susceptible to chlorate-induced toxicity reduced chlorate and nitrate more rapidly than did resistant plants. In experiments testing the potential of this assay, wheat and barley (Hordeum vulgare L.) cultivars previously reported to have low NRA were less susceptible to chlorate-induced toxicity than were cultivars reported to have high NRA. The assay was used to screen 15 soft red winter wheat cultivars for differences in sensitivity to chlorate-induced toxicity. Variable toxic reactions were observed both among and within the cultivars. To determine whether the within-cultivar variation was environmental or genetic, single plant selections for contrasting chlorate response were made, and bulked progeny were rescreened. In eight of 15 cultivars, the contrasting selections were different for chlorate-induced toxic response, indicating heterogeneity for this trait within these eight cultivars. These chlorate-selected lines may also be near-isogenic lines for NRA. Seedling screening of wheat for chlorate response may be useful for identification of high NRA breeding lines.