An exploratory survey of the ecology of Rhizobium meliloti in inland New South Wales and Queensland

Abstract

The ability of Rhizobium meliloti occurring naturally at 26 sites to nodulate three test species of Medicago was investigated. Bacteria able to nodulate Medicago sativa L. were found, in the absence of this host, at all sites sampled and frequently in appreciable numbers, even under dry conditions. Bacteria able to nodulate Medicago denticulata Willd. were found at 25 sites, but usually in lower numbers; they also occurred independently of this species. Organisms able to nodulate Medicago laciniata (L.) Mill. were detected at 18 sites but only in low numbers; they were found at eight sites in the absence of M. laciniata and were not detected at three sites where this medic was present.

High numbers of bacteria able to nodulate M. sativa and M. denticulata were related to high frequencies of Medicago minima (L.) Bart. in the field.

Associations were found between high numbers of Rh. Meliloti in the topsoil and the texture of the soil, the plant size of the annual species of Medicago in the sample area, and the condition of the native grasses.