Diverse symbiotic relationships of Root Nodule Bacteria isolated from endemic SW WA legumes, and importance for development of inoculant strains for nursery production of native legumes

Peter A Howe

Legumes are an important part of the pioneer plant suite, and thus are also important to the revegetation industry, nursery production of legumes is a requirement to fill this need for legumes. The importance of legumes in revegetation is further increased in regions such as the Southwest Australian Biodiversity Hotspot (SWABH), where the diversity of legumes is even greater, requiring a greater range of species to be included in a revegetation project. Specialist nurseries (such as Geographe Community Landcare Nursery in Busselton WA) supply plants to revegetation projects across the state, as well as to domestic gardens. Legumes by their nature require more nitrogen than non-legumes to produce a saleable plant, the most cost effective source for this nitrogen is biological nitrogen fixation. Unlike the situation with agriculturally important legumes, there are no commercial inoculum strains available to the nursery industry for native legumes, and there has been little research into host range and effectiveness of RNB strains inoculating legumes, particularly in the SWABH. Therefore, this project aimed to assess the need and potential cost benefit of biological nitrogen fixation in the nursery context. Target legumes for investigation were selected, and RNB strains were collected from these target legumes over multiple sites. Nursery trials were conducted to determine host range and N2 fixing effectiveness of selected representative RNB strains from those collected. This project collected and isolated 53 phenotypically diverse, potential RNB strains from native legumes growing in the SWABH. All strains collected exhibited morphological and growth rate characteristics of Bradyrhizobium (four representative strains analysed by AGRF confirmed as Bradyrhizobium). From these strains, nine representatives were selected for nursery trials and were inoculated onto the three representative legume species Acacia browniana, Gompholobium confertum and Hovea elliptica from the three major legume groups Mimoseae, Mirbelioid and Brongniartieae, respectively. All nine strains effectively (although at different levels) nodulated A. browniana, 7 strains effectively nodulated G. confertum and only two effectively nodulated H. elliptica. Two RNB strains show promise as commercial nursery inoculum strains with effective nodulation occurring with all 3 species of legumes investigated. One other strain shows further research interest as it was collected from a soil sample with a pH of below 5, where Bradyrhizobium struggle to effectively fix nitrogen.

Diverse symbiotic relationships of Root Nodule Bacteria isolated from endemic SW WA legumes, and importance for development of inoculant strains for nursery production of native legumes

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