Screening Soybeans for Iron Efficiency in the Growth Chamber1

Abstract

Evaluation of soybean genotypes for iron efficiency usually has been done in the field. A quick and repeatable method of evaluating soybean genotypes in the greenhouse or growth chamber is desirable due to variable results in the field and the opportunity for evaluation in the winter. Ten soybean [Glycine max (L.) Merr.] genotypes were evaluated for Fe efficiency in a Canisteo clay loam (Typic Haplaquoll, fine‐loamy mixed, calcareous) in the field and in the growth chamber. They were also evaluated in six Fe‐stress nutrient solutions in the growth chamber. The concentrations of Fe (1.8 or 3.6 µM), CaCO3 (0 or 2.5 mM), and P (130 or 200 µM) were varied in the nutrient solutions with the intent of identifying which combination of these nutrients would give chlorosis symptoms comparable to those found in the field. Visual scores ranging from 1, completely green, to 5, bleached yellow, were determined on the first four trifoliolate leaf stages in the growth chamber studies and on the fourth trifoliolate leaf stage in the field study. Plants at the second trifoliolate leaf stage in the growth chamber showed the greatest degree of chlorosis, and evaluation of genotypes was most effective at this stage. Chlorosis symptoms were much less severe in the growth chamber than in the field, when calcareous soil was the growth medium. The use of calcareous soil in the growth chamber appears to be inadequate for determining Fe‐efficiency of soybeans. The 1.8 µM concentration of Fe and the 2.5 mM concentration of CaCO3 provided an adequate medium for depicting differences among genotypes in the nutrient solutions. The low concentration of Fe and the pH control of CaCO3 resulted in an Fe‐stress similar to that in the field. The 200 µM concentration of P resulted in greater Fe‐stress but was not necessary for differentiating among genotypes for Fe‐efficiency. Of the 10 genotypes, ‘Hawkeye’ and ‘Swift’ were most Fe‐efficient; ‘Hodgson’ and ‘Chippewa 64’ were moderately Fe‐efficient; ‘Harcor’, ‘Corsoy’, ‘Hark’, ‘Anoka’, and ‘Altona’ were Fe‐inefficient; and PI 54619 as highly Fe‐inefficient.