Angiosperm Gymnostoma trees produce root nodules colonized by arbuscular mycorrhizal fungi related to Glomus

Structure and fungal composition is presented here for 'mycorrhizal' nodule s of two angiosperms of the genus Gymnostoma (Casuarinaceae), G. deplanchea num and G. nodiflorum. These species are endemic to New Caledonia, where th ey grow on ultramafic soils. The mycorrhizal nodules, which are modified la teral roots invaded by an arbuscular mycorrhizal fungus, occur in addition to N-2-fixing nodules. Techniques included PCR amplification of extracted DNA, for species identif ication, and histological studies to compare the developmental pathway of G ymnostoma mycorrhizal nodules with that of actinorhizal nodules. The fungal DNA suggested that the strain belongs to the genus Glomus (Gloma les). The endophytic mycelium also contained typical Glomus arbuscules and hyphal coils. Structurally, Gymnostoma mycorrhizal nodules are similar to t hose described in some Coniferales and in Caesalpinioideae trees of French Guyana. The mycorrhizal nodules of G deplancheanum and G nodiflorum contain a fungu s belonging to the Glomales. The role of the nodules might be linked to the ecological situation of the host plants, which are pioneers in exposed and rocky habitats.