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.

Identification and mapping of genomic regions controlling quantitative trait loci (QTLs) was undertaken to determine the genomic regions associated with milling traits in rice to facilitate breeding of new rice varieties with high milling quality. The recombinant inbred (RI) population used was derived from cross of a japonica variety, ‘Asominori’, with an indica variety, ‘IR24’ through 289 RFLP markers. Three milling traits, namely, brown rice percentage (BRP), milled rice percentage (MRP), and milled head rice percentage (MHP), which are the main indicators of milling quality in rice, were estimated for each RI line and their parental varieties. Continuous distributions and transgressive segregations of three milling traits were observed in the RI population, showing that the three traits were quantitatively inherited. Two QTLs (q BRP-9 and q BRP-10) for BRP were identified and mapped to chromosomes 9 and 10, and explained 7.2 and 21.3% of the total phenotype variation, respectively. Two QTLs (qMRP-11 and qMRP-12) governing MRP were detected and mapped to chromosomes 11 and 12, accounted for 12.2 and 7.7% of total phenotype variation, respectively. In addition, three QTLs (qMHP-1, qMHP-3 and qMHP-5) controlling MHP were observed and mapped to chromosomes 1, 3 and 5, and explained 16.0, 22.1 and 8.7% of the total phenotype variation, respectively. Among them, five QTLs (q BRP-9, q BRP-10, qMRP-11, qMHP-3 and qMHP-5) from japonica parent, Asominori, and two QTLs (qMRP-12, qMHP-1) from indica IR24 can improve milling quality in rice. The results and the tightly linked molecular markers that flank the QTL will be useful in breeding for improvement of milling quality in rice.

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.

sponse in the rice seedling stage in a recombinant inbred (RI) population derived from a cross of a japonica variety, Asominori (lower GA3 response), with an indica variety, IR24 (higher GA3 response), using 289 RFLP markers. Continuous phenotypic variation of GA3 response index and transgressive segregation in both parental directions were observed, suggesting that GA3 response in regard to seedling plant height was a quantitatively inherited trait in the RI population. Five QTLs controlling GA3 response were identified and mapped to chromosomes 1, 3, 4, 6 and 12, respectively. Among them, the largest effect QTL (qGAR-1), located between G2200 and C86 on chromosome 1, explained 28.2–34.1% of the total phenotypic variation. The second largest effect QTL (qGAR-12) was detected near C751 on chromosome 12 and accounted for 13.2–16.5% of total variation. The remaining three QTLs on chromosome 3, 4 and 6, explained 5.1–6.4% of total phenotypic variation, respectively. In addition, alleles with increasing and decreasing GA3 response effects were detected from both parents. The molecular markers tightly linked to GA3 response QTLs lead to the isolation of loci and will help us to better understand GA3 response mechanisms in rice.