MODIFIED PROCEDURES FOR COMMERCIAL ADAPTATION OF ROOT IRON-REDUCING CAPACITY AS A SCREENING TECHNIQUE

Genotypic evaluation is critical to development of soybean [Glycine ma x (L.) Merr.] cultivars with genetic resistance to Fe-deficiency chlor osis. Root Fe3+ reducing activity is correlated with genotypic resista nce to Fe chlorosis measured in field nurseries, and thus may be a rel iable method for identifying chlorosis-resistat genotypes. However, to develop methods useful for large-scale screening, several modificatio ns of the previously published procedure for measuring root Fe3+ reduc ing activity were investigated. Several hydroponic experiments were co nducted to test proposed modifications. It was determined that: (a) di fferent genotypes may be grown together in the same nutrient solution without affecting Fe3+ reduction, (b) genotype separation is maximized by growth in CaCO3 buffered solution (37.5 mg L(-1)), (c) a labor-int ensive elongation step can be eliminated, and (d) denotype evaluation can be accomplished without introducing Fe into the hydroponic solutio ns. These refinements to the procedure should allow its adaptation and use in soybean breeding programs.