MOLECULAR MARKERS LINKED TO GENES UNDERLYING SEEDLING TOLERANCE FOR FERROUS IRON TOXICITY

A double haploid (DH) population consisting of 123 lines derived from a japonica variety, Azucena, and an indica variety, IR64, and 100 BC1F 1 (Azucena) lines were cultivated hydroponically using two treatments: one with excess Fe2+ at the concentration of 250 mg L-1 and a control with standard nutrient solution. Genotypic tolerance was evaluated us ing an index scale based on degree of leaf bronzing and relative decea se in shoot dry weight (RDSDW) Toxic symptoms were not observed for Az ucena and BC1F1 plants. In contrast, index values for the DH populatio n indicated segregation for tolerance, and IR64 was moderately sensiti ve. Molecular marker loci associated with variations in index values a nd in RDSDW, and gene loci for tolerance were detected using 175 Marke rs mapped on all 12 chromosomes by single marker loci and interval map ping. Two gene loci were identified to be flanked by RG345 and RG381, and linked to RG810, respectively, on chromosome 1 for both index valu es and RDSDW. They explained 32% and 13% of the total variation in the index values, and 15% and 21% in the RDSDW in the population, respect ively. The variation in RDSDW was also explained by a locus linked to RG978 on chromosome 8 by about 10%. Comparison of the two marker genot ypic class means indicated that the tolerant alleles were from Azucena at the first locus on chromosome 1 and the locus on chromosome 8, and that at the second locus on chromosome 1 from IR64.