Occurrence of both Casuarina-infective and Elaeagnus-infective Frankia strains within actinorhizae of Casuarina collina, endemic to New Caledonia

Abstract

New Caledonia is characterized by an exceptional concentration of endemic Casuarinaceae species including eight Gymnostoma species and Casuarina collina. Frankia strains isolated from nodules from C. collina have been studied through a range of techniques including molecular typing, infectivity/effectivity and host spectrum. All these isolates had characteristics similar to those of atypical Frankia from Casuarina previously described. This work evidenced several original features within these 26 isolates: (i) they are localized inside the nodule; (ii) they fit into the Elaeagnus-infective Frankia group; (iii) they belonged to four ITS groups already described for Frankia from Gymnostoma. In fact, it is highly probable that atypical Frankia from C. collina and Frankia from Gymnostoma are the same. We can formulate the hypothesis that the Frankia from Gymnostoma could use C. collina as an alternative host in absence of Gymnostoma spp. or when the ecological conditions are favourable to C. collina.