Isolation, characterisation (PCR-RFLP) and specificity of Frankia from eight Gymnostoma species endemic to New Caledonia.

Eight Frankia-Gymnostoma nitrogen-fixing symbioses endemic to New Caledonia were studied using a range of techniques including molecular typing of Fra nkia, infectivity/effectivity and host spectrum of the isolates. The study was conducted on 128 Frankia isolates from the eight Gymnostoma species. Th e RFLP analysis of the rRNA 16S-23S ITS allowed us to cluster the strains i n four groups. Symbiotic characterization of the four groups failed to reve al any host specificity both in term of infectivity or effectivity. The cha racteristics of the strains were those of Eleagnaceae-infective Frankia str ains. Co-inoculation of two Gymnostoma species with mixtures of strains evi denced 11 % of mixed RFLP profiles. In such controlled conditions, this was interpreted as co-infections. This work evidenced original features of the se Gymnostoma isolates: (i) they were closer to Eleagnaceae-infective Frank ia than Casuarina-infective Frankia; (ii) closer to atypical Frankia from C asuarina; (iii) poorly host-specific; and (iv) they had a tendency of co-in fection. They could represent a primitive group of Frankia able to survive in a wide range of habitats. (C) 2000 Editions scientifiques et medicales E lsevier SAS.