Genetic variation in the effictiveness of nodulation of lucerne varieties

Abstract

The effectiveness of the nodulation of 15 varieties of lucerne, inoculated with single strains of Rhizobium meliloti of widely differing origin, was examined in test-tube culture under glass-house conditions. The principal findings were that: (i) Some varieties were more effective in their symbiosis with these bacterial strains than others. (ii) Some bacterial strains were generally more effective in their symbiosis with these varieties than others. (iii) Highly significant host variety x bacterial strain interactions required that the generalizations regarding varieties and bacterial strains should be interpreted with caution. The variety Rambler was unable to form an effective symbiosis with any of the Australian strains of Rh. Meliloti tested, although two isolates from nodules of Canadian-grown Rambler plants achieved a reasonable level of effectiveness in their symbiosis with this variety. Considerable variation existed within variety x strain treatments; this variation was greatest in the treatments designated as "intermediate" in their effectiveness of nodulation. The significance of the results is discussed, and a plan for the breeding of legumes, in which nodulation aspects are considered, is suggested.