Nodulation studies on legumes exotic to Australia: Lupinus and ornithopus spp.

In a series of glasshouse and field experiments, the symbiotic characteristics of 24 lines of Lupinus and Ornithopus species and 20 strains of Rhizobium lupini were defined. Rhizobium lupini inoculant established readily in several soils and lupins grown in the field responded to inoculation by improved nodulation, growth and yield. It is concluded that lupin crops sown on new land need to be inoculated to achieve optimum yield. At three sites, field-grown lupins responded to increasing rates of inoculation up to the rate recommended by the inoculant manufacturer. At two of the sites there was no further response to higher rates, but at the third there was a continuing response up to 125x (inoculation rate). Lupin seed was preinoculated, using gum arabic adhesive, up to 33 days before sowing without significant loss of viability or nodulating capacity of the inoculant. Seed coating with several materials did not improve inoculant viability on preinoculated seed. In glasshouse experiments, hostxstrain interactions in nitrogen fixation were frequent and substantial. They occurred at three levels of taxonomic relationship, viz, between the genera Lupinus and Ornithopus, between different species within the same genus, and between different lines of the same lupin species. Hostx strain interactions were also observed in field experiments but were less frequent and smaller than in the glasshouse. These observations have implications for the 'single-strain inoculant policy that applies to the manufacture of commercial lupin and serradella inoculant in Australia.