Sensitivity of selected Frankia isolates from Casuarina, Allocasuarina and North American host plants to sodium chloride

Three experiments examined the effects of NaCl concentrations 0 to 500 mM on the growth of isolates of Frankia from Casuarinaceae and selected North American host plants. Four Casuarina isolates grew well in defined medium (pyruvate‐BAP) but not in a yeast extract medium. Conversely the non‐Casuarina isolates preferred the yeast‐extract medium, although two of them grew in the defined medium. When grown in their preferred medium, the Casuarina isolates were little affected by NaCl concentrations up to 200 mM but did not grow at 500 mM. The non‐Casuarina isolates, with the exception of an isolate from Purshia tridentata. were severely affected above 50 mM NaCl. Nitrogenase activity (C2H2 reduction) by the non‐Casuarina isolates could not be detected in low‐N medium although protein determinations indicated that a low level of nitrogen fixation had occurred. All four Casuarina isolates showed nitrogenase activity in culture, up to 200 mM NaCl, although at that concentration of NaCl, growth was affected more than that of cultures in N‐supplemented medium. All four strains showed a marked increase in nitrogenase activity up to 72 h after the addition of C2H2, with the magnitude of the effect and their subsequent behaviour being strain dependent. The results indicate that the isolates of Frankia from Casuarina and Allocasuarina, and that from Purshia tridentata, are more tolerant of NaCl than isolates from species not normally growing under sodic conditions. They provide optimism that these strains could successfully establish in saline soils if introduced with species of host plants tolerant to these soils.