Salinity and waterlogging tolerance amongst accessions of messina (Melilotus siculus)

Melilotus siculus (common name messina) has shown potential as a productive annual forage legume in saline and waterlogged areas in temperate Australia. The salt and waterlogging tolerances of 30 M. siculus accessions were evaluated at germination and as established plants. Many accessions germinated at 240mM NaCl, but germination was <15% at 320mM NaCl. In vegetative plants, accessions differed in the degree of growth reduction at 300mM NaCl, with some producing >90%, but others <20%, of non-saline controls. A negative relationship (r = 0.47, P < 0.001) was found between dry weight under non-saline conditions and relative salt tolerance (i.e. salt-treated as % of controls). Concentrations of Cl- and Na+ in shoots of all accessions increased significantly with increasing NaCl in the medium, although these differed among accessions. No relationships were found between shoot Cl-, Na+, or K+ concentrations and relative salt tolerance at 300mM NaCl, whereas net K+ : Na+ selectivity to shoots was positively correlated with relative salt tolerance (r = 0.30, P = 0.1). All accessions showed good tolerance to stagnant, O-2-deficient conditions in the root medium, and shoot growth was not reduced by >20% in any accession. Root porosity (% gas volume/root volume) in both the main and lateral roots increased in all accessions when in stagnant medium, but accessions differed in root porosity. Lateral root porosity was not, however, correlated with either shoot dry weight or root dry weight in stagnant conditions. No single accession of M. siculus had the highest tolerance to saline conditions both at germination and the vegetative stage, but some accessions (e.g. SA 40002 and SA 40004) performed consistently well under saline and waterlogged conditions. Further research and selection is warranted on these accessions with the aim to release a cultivar.