Use of bicarbonate in screening soybeans for resistance to iron chlorosis

Abstract

Abstract Six bicarbonate and 2 Fe levels were used in nutrient solution to determine the optimum treatment combination for detecting small differences in Fe chlorosis resistance among soybean cultivars. The cultivars tested represented chlorosis resistant (Lakota, Hawkeye, Chippewa‐64, and Hodgson) and chlorosis susceptible (Williams, Hark, Anoka, and Wayne) classes, based on reported field scores. Treatments consisted of a factorial arrangement of 0, 5, 10, 15, 20, or 25 mM NaHCO3 and 4 or 6 μM FeEDDHA, with a 1:2 Fe:chelator ratio. All plants were grown in a modified 1/5 Johnson solution containing excess CaCO3 and 400 μM P, with NO3 ‐N. Five mM increments of HCO3 ‐ increased the chlorosis severity in all cultivars at both Fe concentrations. Orthogonal polynomial analysis indicated that the rate of chlorosis increase was greatest at HCO3 ‐ levels less than 10 mM. Chlorosis was more severe at 4 than 6 μM Fe. At low Fe and high HCO3 ‐ , even resistant cultivars became chlorotic. For germplasm screening, the 6 μM Fe, 15 mM HCO3 ‐ treatment provided the best chlorosis class separation and closest relationship to average field observations.