Rapid improvement of salinity tolerance in the Oryza sativa L. cv. Yukinko-mai

Salinity critically limits rice growth, metabolism and productivity worldwide. Improvement of salt-resistant of locally adopted high yielding rice cultivars is time demanding issue to ensure emerging global food demand. In this study, we precisely introgressed hst1 gene conferring salinity tolerance from 'Kaijin' into 'Yukinko-mai' (WT) rice that is excellent in yield stability through single nucleotide polymorphism (SNP) marker-aided backcrossing. Applying a speed breeding technique (modified biotron breeding system), the BC3F3 population were developed within 17-month and named 'YNU31-2-4'. The high-resolution genotyping by whole-genome sequencing explored that the BC3F2 genome has 93.5% similarity with WT and it fixes only 2.7 % of donor parent alleles. The functional annotation of BC3F2 variants along with the field assessment data indicates, 'YNU31-2-4' possessing agronomic traits most like the WT and no apparent grain yield reduction was related with the presence of hst1 gene. Under 125mM NaCl stress, the YNU31-2-4 seedlings showed significantly higher survival rate, shoot and root length and biomass compared with WT, suggesting the strong salt-resistant similar to that of the Kaijin. Quantitative and electron probe microanalyzer studies indicated 'YNU31-2-4' significantly avoided Na+ accumulation in shoot under salt stress. The 'YNU31-2-4' plants also exhibited improved phenotype with significantly higher net CO2 assimilation rate and lower (45%) yield decline than WT, exposed to salt-stress during the reproductive stage. In conclusion, 'YNU31-4' is a potential candidate of new rice cultivar with markedly improved salinity tolerance, which might be sustain yield under changing climate.