Studies onRhizobiumstrains

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Abstract
The influence of a number of authenticated strains of Rhizobium meliloti on lucerne has been studied. In relation to interaction with three varieties of lucerne it was shown that cwo widely used strains (ML5 and U45) are able to establish equally satisfactory symbiosis on the three genetically diverse lucerne varieties—Marlborough, Rambler, Glutinosa. Some strains were, however, marc specific in respect to host plant, and a problem exists in securing effective nodulation on the creeping types of lucerne wherein the secondary growth of such plants becomes dissociated from the centre of primary nodulation. In a study of 20 strains on field plots of lucerne, some consistently held a rating in a top group of effectiveness. From the nodulation patterns exhibited some characteristics of these effective strains were revealed. When the growth of lucerne was measured in soil adjusted through a range of pH from 4.2–7.5, most rhizobia were effective only at pH levels of 6.5–7.5, although there was evidence that some declined at a pH above 6.5. Others had a measure of tolerance of moderate acidity (pH 5.0–5.5).