MAPPING GENETIC-LOCI FOR IRON-DEFICIENCY CHLOROSIS IN SOYBEAN

The objective of this study was to map genes controlling iron deficien cy chlorosis in two intraspecific soybean [Glycine max (L.) Merrill] p opulations. Chlorosis symptoms were evaluated by visual scores and spe ctrometric chlorophyll determinations at the V4 stage (third trifoliol ate leaf fully developed) in the field in 1993, and at V2 (first trifo liolate leaf fully developed) and V4 stages in 1994. A total of 89 RFL P 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 p opulation were used to map quantitative trait loci (QTL) affecting ira n deficiency chlorosis. QTL with minor effects were detected on six li nkage 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 linkag e group N. Another QTL for visual score variation, and one for chlorop hyll 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 int o qualitative data fitting a one major gene model according to the mea ns 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 segr egation for iron chlorosis deficiency in the Anoka x A7 population. Th is study supported a previous hypothesis that two separate genetic mec hanisms control iron deficiency in soybean.