A salt-sensitive mutant designated rice salt sensitive 2 （rss2） was isolated from the M2 generation of the rice cultivar Nipponbare （Oryza sativa L. ssp. japonica） mutagenized with ethyl methanesulfonate （EMS）. This mutant exhibited a greater decrease in salt tolerance with a significant increase in Na＋ content in its shoots. Genetic analysis indicated that the increase in Na＋ in rss2 was controlled by a single recessive gene. Further genome-wide analysis of the linkage map constructed from the F2 population of rss2/Zhaiyeqing 8 （ZYQ8） showed that two quantitative trait loci （QTLs） on chromosomes 1 and 6 were responsible for the Na＋ concentration in shoots, which explained 14.5% and 53.3%, respectively, of the phenotypic variance. The locus on chromosome 1, but not that on chromosome 6, was also detected in the F2 population of Nipponbare/ZYQ8, suggesting that the QTL on chromosome 6 was responsible for the salt sensitivity in rss2. By analyzing the recombination events in 220 mutant individuals of an enlarged mapping population of rss2/ZYQ8, the rss2 locus was precisely mapped to an interval of 605.3 kb between insertion/deletion （InDel） markers IM21962 and IM22567. This finding will facilitate the cloning of the rss2 locus and provide insight into the physiological mechanisms of salt sensitivity in rice.
