Genotypic Evaluation for Iron Deficiency Chlorosis in Soybeans by Visual Scores and Chlorophyll Concentration1

A comparison was made of the effectiveness of visual scores (Vs) and concentrations of chlorophyll a (Ca), chlorophyll b (Cb), and total chlorophyll (Cab) for evaluating the response of soybean [Glycine max (L.) Merr.] genotypes to Fe deficiency chlorosis. A total of 400 entries, including breeding lines, parents, and check cultivars, were evaluated in replicated tests on calcareous soils at two locations in Iowa. Visual scores and chlorophyll concentration were determined on the first trifoliolate leaf when it was fully developed. Visual scores ranged from I, no yellowing, to 5, severe yellowing, and chlorophyll concentration in mg dm‐2 leaf area was determined by acetone extraction. There were significant differences among entries for the four characters. Highly significant correlations from 0.97 to 0.99 were observed among Ca, Cb, and Cab. Vs had highly significant negative correlations from −0.89 to ∓0.90 with the chlorophyll concentrations on an entry mean basis. The four characters were equally effective in selecting lines with superior chlorosis resistance on the basis of simulated selection experiments. Vs would be the most efficient procedure for direct comparison of genotypes because it requires considerably less labor than chlorophyll determination. Chlorophyll determination may be preferred, however, for research studies in which an objective measure of chlorosis is needed, particularly if different environments and persons are involved.