The practice of inoculating forage legumes with rhizobia strains is widespread. It is assumed that the inoculated strain determines the performance of the symbiosis and nitrogen fixation rates. However, native-naturalized strains can be competitive, and actual nodule occupancy is often scarcely investigated. In consequence, failures in establishment, and low productivity attributed to poor performance of the inoculant may merely reflect the absence of the inoculated strain in the nodules. This study lays out a strategy followed for selecting a Rhizobium leguminosarum sv. trifolii strain for white clover ( Trifolium repens ) with competitive nodule occupancy. First, the competitiveness of native-naturalized rhizobia strains selected for their efficiency to fix N 2 in clover and tagged with gus A was evaluated in controlled conditions with different soils. Second, three of these experimental strains with superior nodule occupancy plus the currently recommended commercial inoculant, an introduced strain, were tested in the field in 2 years and at two sites. Plant establishment, herbage productivity, fixation of atmospheric N 2 ( 15 N natural abundance), and nodule occupancy (ERIC-PCR genomic fingerprinting) were measured. In both years and sites, nodule occupancy of the native-naturalized experimental strains was either higher or similar to that of the commercial inoculant in both primary and secondary roots. The difference was even greater in stolon roots nodules, where nodule occupancy of the native-naturalized experimental strains was at least five times greater. The amount of N fixed per unit plant mass was consistently higher with native-naturalized experimental strains, although the proportion of N derived from atmospheric fixation was similar for all strains. Plant establishment and herbage production, as well as clover contribution in oversown native grasslands, were either similar or higher in white clover inoculated with the native-naturalized experimental strains. These results support the use of our implemented strategy for developing a competitive inoculant from native-naturalized strains.

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In the high-rainfall zone of Australia (HRZ, >600 mm), most pasture systems are dominated by perennial grasses with low levels of inter-dispersed legume. Numerous authors have shown that a legume content of 20–50% is required to maximise livestock production. Consequently, the legume content of these systems needs to be increased if livestock production is to be improved. Perennial legume options such as lucerne (Medicago sativa) and white clover (Trifolium repens) are limited in their application in this zone due to the sensitivity of lucerne to acid soils (pH(CaCl2) <4.8) and waterlogging and the inability of white clover to survive most of the annual summer droughts. To address this problem, a breeding program was undertaken to develop varieties of Lotus corniculatus (birdsfoot trefoil) suitable for the HRZ of southern Australia. In the first cycle, 365 populations were screened in nurseries to select the best 62 plants from the best populations at Yalanbee and Medina in Western Australia. These selections were then grown as half-sib families in spaced-plant nurseries at Waroona and Yalanbee; in the second cycle, 61 individuals, selected from the the two sites, were hand-crossed to produce 3160 plants from 202 pair-crosses. These were gown in a spaced-plant nursery at the University of Western Australia Field Station in Shenton Park. In the third cycle, three polycross populations (YF, T, and F) were produced from selections within the 3160 second-cycle plants, and two additional plants which survived for 4 years on a non-wetting sand at Yalanbee, including a significant drought year in 2006. These varieties are expected to extend the adaptation of L. corniculatus to drier areas and/or lower latitudes.