Excess zinc harms the growth of rice plants and zinc toxicity can easily occur in acid soils. The aim of the study was to map quantitative trait loci (QTLs) in rice for tolerance to zinc toxicity, using a recombinant inbred (RI) population derived from the cross of a japonica variety (Asominori: relatively tolerant to Zn2+ toxicity) with an indica variety (IR24, relatively susceptible), through 289 RFLP markers. The index scores of damage (representing Zn2+ toxicity tolerance), after irrigating rice seedlings with a 1000-ppm Zn2+ solution for 20 successive days, were examined for each RI line and its parental varieties. Continuous distributions and transgressive segregations of the index scores were observed in the RI population, suggesting that Zn2+ toxicity tolerance was a quantitatively inherited trait. Three QTLs for Zn2+ toxicity tolerance were detected on chromosomes 1, 3 and 10 and explained 21.9, 8.9 and 7.6%, respectively, of the total phenotypic variation. The results and the tightly linked molecular markers that flank the QTLs, detected in this study, will be useful in improving Zn2+ tolerance in rice. In addition, the genomic positions between QTLs for Zn2+ toxicity tolerance and the QTLs for other metal (Fe2+, Mn2+, Al3+) toxicity tolerances, from previous studies, are discussed.

Phenolic acids are secondary metabolic organic compounds produced by plants and often are mentioned as allelochemicals. This study was conducted to determine the genetic basis controlling the ferulic acid content of rice straw in a recombinant inbred (RI) population derived from a cross between a japonica variety, Asominori, with a higher content of ferulic acid, and an indica variety, IR24, with a lower content, using 289 RFLP markers. Continuous distributions and transgressive segregations of ferulic acid content were observed in the RI population, which showed that ferulic acid content in rice straw was quantitatively inherited. Single marker analysis and composite interval mapping identified three quantitative trait loci (QTLs) for ferulic acid content with LOD values of 2.03 (chromosome 3), 3.16 (chromosome 6), and 3.06 (chromosome 7); all three had increased additive effects (13.5, 18.3, and 18.1 μg g−1) from the Asominori parent and accounted for 5.5, 16.9, and 12.8% of total phenotypic variation, respectively. This is the first report on the identification of QTLs associated with ferulic acid and their chromosomal localization on the molecular map of rice. The tightly linked molecular markers that flank the QTLs might be useful in breeding and selection of varieties with higher phenolic acid content.

The development of molecular genetic maps has accelerated the identification and mapping of genomic regions controlling quantitative trait loci(QTL) in rice (Oryza sativa L.). Minimizing embryo size in rice would increase proportion of edible endosperm.This study was conducted to determine the genetic basis controlling embryo size of rice grains in a recombinant inbred (RI) population derived from cross of a japonica cultivar,Asominori,with an indica cultivar,IR24,by means of 289 restriction fragment length polymorphism (PFLP)markers.Two parameters,embryo length and embryo width,which represent embryo size in rice,were estimated for each RI line and their parental varieties.Continuous distributions and transgressive segregations of embryo length and embryo width in rice were observed in the RI population,suggesting that embryo size was quantitative in grains of conventional varieties.Three QTL for embryo length were detected on chromosomes 1, 2, and 3 explained 17.9, 25.7, and 9.2%, respectively, of the total phenotypic variation. Three QTL for the embryo width were observed on chromosome 2, 8, and 10 and accounted for 13.5, 15.7, and 15.0% of total phenotypic variation, respectively. In addition, alleles with increasing and decreasing effects were detected from the both parents. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for embryo improvement in rice.