Use of bicarbonate in screening soybeans for resistance to iron chlorosis

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.

Key words:

• Glycine max L.
• nutrient solution
• FeEDDHA

Notes

Scientific article no. 3567 contribution no. 6642 of the Maryland Agric. Exp. Stn., Dep. of Agronomy, College Park, MD 20742 and U.S.D.A. Beltsville, MD 20705. This article is from a thesis to be submitted to the Graduate School, University of Maryland, by B. A. Coulombe in partial fulfillment of the requirements for the Master's Degree in Agronomy.