Specificity of association between Bacillus isolates and genotypes of Lolium perenne and Trifolium repens from a grass – legume pasture

Specificity between plants and associated rhizosphere bacteria was investigated using species and genotypic mixtures of Lolium perenne L. (perennial ryegrass) and Trifolium repens L. (white clover) inoculated with Bacillus strains isolated from rhizosphere soil of the pasture plants. The genotypic identity of plants was controlled by using stolon tips (Trifolium) and tillers (Lolium) of three genotypes of each species collected from a 45-year-old permanent pasture. Inoculation of plants in the greenhouse with Bacillus isolates that had coexisted in the field with the Lolium component of a Lolium–Trifolium mixture increased Lolium root and shoot weight. Root and nodule weight of Trifolium in mixture regardless of its genotype was also higher when coexistent Bacillus–Lolium combinations were present. The presence of other coexistent Bacillus–plant or plant–plant combinations did not enhance performance of either pasture species. The identity of the Rhizobium leguminosarum biovar trifolii strains that formed Trifolium root nodules was unaffected by inoculation with Bacillus. Key words: Trifolium repens, Lolium perenne, Bacillus, specificity, rhizosphere, yield.