The rhizobia of lupinus densiflorus Benth., with some remarks on the classification of root nodule bacteria

Abstract

Four strains of rhizobia from Lupinus densiflorus Benth. were found to differ from the normal slow-growing strains of Rhizobium lupini by a rapid growth on agar medium, a somewhat different pattern of carbon metabolism, good growth in simple synthetic media, and also in their host plant relationships. Three strains had subpolar flagella like other lupine rhizobia, and the same was found to be predominant in a fourth strain previously described as having peritrichous flagellation. Two strains formed effectively nitrogen-fixing root nodules in Lotus corniculatus and Anthyllis vulneraria where the other two formed semieffective or ineffective nodules. All four strains formed ineffective nodules in Lotus uliginosus and Ornithopus sativus. The slow-growing strains of Rh. lupini mostly produce ineffective nodules in Lotus corniculatus but have now been seen to be effective in Lotus uliginosus. Instead of trying to define Rh. lupini as a “cross-inoculation” group it seems preferable to abandon it as a species and to transfer the fastgrowing strains to Rhizobium leguminosarum sensu Graham (1964) and De Ley and Rassel (1965), in spite of their predominantly subpolar flagellation. The familiar slow-growing strains would remain in the broad group of slow-growing root nodule bacteria with purely subpolar flagellation, called Phytomyxa japonica by Graham (1964) and Rhizobium japonicum by De Ley and Rassel (1965).