Variation in salinity tolerance, early shoot mass and shoot ion concentrations within Lotus tenuis: towards a perennial pasture legume for saline land

Perennial legumes are needed for productive pastures in saline areas. We evaluated 40 lines of Lotus tenuis for tolerance to salinity at both germination and vegetative growth stages. Salt tolerance during the early vegetative stage was assessed in a sand-tank experiment with NaCl concentrations of 0-450mM NaCl for 5 weeks. Most L. tenuis lines were more salt tolerant and had at least 50% lower shoot Na+ plus Cl- (% dry mass (DM)) compared with some other common pasture legumes, Medicago sativa, M. polymorpha and Trifolium subterraneum. Within L. tenuis significant variation in salt tolerance was found, with C-50 values (concentrations of NaCl that decreased shoot dry matter to 50% of control) ranging from similar to 100 to 320mM. Shoot concentrations of Cl-, Na+ and K+ did not always correlate with salt tolerance; some tolerant lines had low shoot Na+ and Cl- (and thus better nutritive value), while others tolerated high shoot Na+ and Cl-. We also found variation within L. tenuis for salt tolerance of seeds, with lines ranging from 0 to 70% germination after recovery from a prior exposure to 800mM NaCl for 15 days. There was no relationship between salinity tolerance of scarified seeds and subsequent growth of seedlings; therefore, testing of seeds alone would not be an appropriate screening method for salt tolerance in L. tenuis. This study of 40 L. tenuis lines has shown significant genetic variation for salt tolerance within this species, and we have identified key lines with potential to be productive in saltland pasture systems.