Symbiotic characteristics of Rhizobium trifolii from Israel in association with 10 species of Trifolium*

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Abstract
The symbiotic properties of 25 isolates of Rhizobium trifolii were tested in bacteriologically controlled culture with populations of 10 Trifolium species. The rhizobia had been isolated from nodules of the same 10 populations grown on three soil types occurring in Israel. All host plant x R. trifolii isolates formed nodules, but the symbiotic effectiveness varied greatly. Twenty-one isolates formed at least one highly effectivc symbiotic combination and the two best isolates each formed four. On the basis of similar symbiotic behaviour, the 25 isolates fell into not less than 10 distinct groups. Some degree of strain specificity in effectiveness of nitrogen fixation existed in all species except T. repens. Bacterial associations with T. batmanicurn, T. pauciflorum and T. spumosum were highly specific. Over all isolates, T. alexandrinurn was more effective in symbiosis than other species. T. repens performed poorly. T. echinatum, T. alexandrinum, and T. spumosum were similar in their patterns of symbiotic response, and so were T. pauciflorum, T. glomeratum, and T. brachycalycinum. Howeker, host groupings were less well defined than R. trifolii isolatc groupings. Some confirmation was obtained of earlier reports that, in the presence of a heterogeneous soil population of R. trifolii, a clover plant tends to be nodulated by the more effective strains. A negative correlation was found between the mean effectiveness of rhizobia isolated from a particular species and the mean response of that species to all of the isolates. __________________ *Publication of the Agricultural Research Organization (State of Israel, Ministry of Agriculture), 1975 Series, No. 235-E.