POPULATIONS OF RHIZOBIA IN NEW ZEALAND SOILS

Abstract

ALTHOUGH LEGUMES are of prime importance in New Zealand pastures, the number of species involved is small, and is restricted almost entirely to the genera Trifolium (the clovers), Medicago (lucerne and other medics), and Lotus. These three genera form nodules with three separate groups of rhizobia (root nodule bacteria) with no effective crossnodulation between them. Also, within any one of these groups of rhizobia, there are numerous strains. These may differ in a number of respects, but in particular they differ in the range of species with which they are effective in fixing nitrogen. Thus, among clover rhizobia, one strain may be effective on white (Trifolium repens L.) and red clovers (T. pratense L.) but not on subterranean clover (T. subterraneum L.), a second strain effective on subterranean, weakly effective on red and ineffective on white clover, and a third strain effective on all three species.