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

New Caledonia is characterized by an exceptional concentration of endemic C asaurinaceae species including eight Gymnostoma species and Casuarina colli na. Frankia strains isolated from nodules from C. collina have been studied through a range of techniques including molecular typing, infectivity/effe ctivity and host spectrum. All these isolates had characteristics similar t o 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 Fra nkia group; (iii) they belonged to four ITS groups already described for Ei Frankia from Gymnostoma. In fact, it is highly probable that atypical Fran kia from C. collina and Frankia from Gymnostoma are the same. We can formul ate the hypothesis that the Frankia from Gymnostoma could use C. collina as an alternative host in absence of Gymnostoma spp. or when the ecological c onditions are favourable to C. collina. (C) 1999 Editions scientifiques et medicales Elsevier SAS.