QTL analysis for sodium removal ability in rice leaf sheaths under salinity using an IR-44595/318 F population.

Over-accumulation of salt in rice plants is an effect of salt stress which decreases growth and grain yield. Salt removal ability in leaf sheaths is a tolerance mechanism to decrease salt entry and accumulation in leaf blades and maintain photosynthesis under salinity. In this study, a QTL analysis of removal ability of sodium ions (Na) in leaf sheaths and Na accumulation-related traits, was conducted using F population between two rice varieties, IR-44595 with superior Na removal ability, and 318 with contrasting Na removal ability in leaf sheaths under salinity. Suggestive QTLs for Na removal ability in leaf sheaths were found on chromosomes 4 and 11. The suggestive QTL on chromosome 11 overlapped with other significant QTLs for Na concentration in shoots, leaf blades and leaf sheaths, and Na/K ratio in leaf blades. Correlation analysis indicated that Na removal ability in leaf sheaths is important in reducing Na accumulation in leaf blades. The varietal difference of Na removal ability in leaf sheaths at the whole plant level was greater at lower NaCl concentrations and became smaller as the treatment NaCl concentration increased. Although the Na removal ability in leaf sheath was comparable between IR-44595 and 318 under high salinity at the whole plant level, the younger leaves of IR-44595 still showed a higher Na sheath-blade ratio than 318, which implied the Na removal ability functions in the younger leaves in IR-44595 to reduce Na entry in young leaf blades even under high salinity.