Dynamic quantitative trait loci for salt stress components on chromosome 1 of rice

Rice varieties Co39 and Moroberekan differ for leaf Na+ concentrations when grown at moderate salinity (100-150 mol m(-3) NaCl; 10 : 1 or 20 : 1 Na+ to Ca2+ ratio). Recombinant inbred lines (RILs) from a cross between them were used to map quantitative trait loci (QTL) under salt stress over several weeks. Two experiments (conducted with 170 and 96 RILs, and a linkage map of 126 RFLP markers) identified a major effect on QTL for leaf Na+ concentration and K+ : Na+ ratio on chromosome 1 in a region corresponding to 11.07-14.6 Mbp. No leaf Cl- QTL were detected. In a third experiment, leaves and sheaths were harvested after 7 and 21 days at 100 mol m(-3) NaCl. The linkage map of chromosome 1 was improved by the addition of 28 microsatellite markers, which resolved distinct QTL for Na+ and K+ concentrations, and K+ : Na+ ratio. After 7 days' stress, the most significant QTL were in the region of 11.56-12.66 Mbp. The highest Na+ concentrations were recorded in the sheaths. Na+ concentrationQTLwere detected for leaves, but not for sheaths. After 21 days' stress, the region containing the most significant QTL extended to 11.07 Mbp in leaves and in sheaths. A QTL for the ratio of leaf Na+ to sheath Na+ concentrations was found at 11.39-12.39 Mbp. These findings suggest that multiple genes in this region are involved in the response to salinity, and their impact is dynamic according to stress duration, and leaf age and type.