Mapping genetic loci for iron deficiency chlorosis in soybean

The objective of this study was to map genes controlling iron deficiency chlorosis in two intraspecific soybean [Glycine max (L.) Merrill] populations. Chlorosis symptoms were evaluated by visual scores and spectrometric chlorophyll determinations at the V4 stage (third trifoliolate leaf fully developed) in the field in 1993, and at V2 (first trifoliolate leaf fully developed) and V4 stages in 1994. A total of 89 RFLP and 10 SSR markers in the Pride B216 x A15 population, and 82 RFLP, 14 SSR and 1 morphological I (hilum color) markers in the Anoka x A7 population were used to map quantitative trait loci (QTL) affecting iron deficiency chlorosis. QTL with minor effects were detected on six linkage groups of the Pride B216 x A15 population, suggesting a typical polygene mechanism. In contrast, in the Anoka x A7 population, one QTL contributed an average of 72.7% of the visual score variation and 68.8% of the chlorophyll concentration variation and was mapped on linkage group N. Another QTL for visual score variation, and one for chlorophyll concentration variation were detected on linkage groups A1 and I, respectively. Due to the large LOD score and major genetic effect of the QTL on linkage group N, the quantitative data was reclassified into qualitative data fitting a one major gene model according to the means of the QTL genotypic classes. The major gene was mapped in the same interval of linkage group N using both visual scores and chlorophyll concentrations, thus verifying that one major gene is involved in segregation for iron chlorosis deficiency in the Anoka x A7 population. This study supported a previous hypothesis that two separate genetic mechanisms control iron deficiency in soybean.