Tissue culture evaluation of NaCl tolerance in Medicago species: Cellular versus whole plant response

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Abstract
Tissue culture responses to three levels of NaCl (0, 85mM and 170 mM) were evaluated in several Medicago species including: M. dzhawakhetica, M. marina, M. rhodopea, M. rupestris, M. sativa (alfalfa) and M. suffruticosa. The whole plant responses of the same genotypes were evaluated in half-strength Hoagland's solution containing 0, 51.5, and 103 mM NaCl. One or more genotypes of M. dzhawakhetica, M. rhodopea, M. rupestris, and M. sativa exhibited in vitro NaCl tolerance at 85 mM. In addition, one genotype each of M. dzhawakhetica, M. rhodopea, and M. sativa was tolerant of 170 mM NaCl. However, all of the genotypes that demonstrated NaCl tolerance in vitro were NaCl sensitive at the whole plant level. Conversely, M. marina the only species exhibiting whole plant NaCl tolerance, had the most NaCl sensitive genotypes at the in vitro level. Although an in vitro NaCl tolerance mechanism which confers whole plant NaCl tolerance was not observed, a potential NaCl tolerance germplasm source, M. marina, was identified.