Clover root-nodule bacteria in the New England region on NSW.

Abstract

Most of the cultures isolated from the New England Region of New South Wales were able to form effective associations with white clover. Associations with red, crimson, and subterranean clovers were of doubtful effectiveness, or definitely ineffective. Isolates from plants growing in the drier ayeas were the most effective symbionts with crimson and subterranean clovers, but those from plants in the wetter areas proved best with red and white clovers. This locality effect seemed to be related to the field host from which the isolate was obtained. Those from clustered and subterranean clover were more effective on crimson and subterranean clovers than were those from white clover. On the other hand white clover isolates were the most effective symbionts for white and red clovers. There was a similarity in the effectiveness of isolates of red and white, subterranean and crimson clovers. There was a significant negative correlation with all other pairs. An unusually large number of cultures was inconsistent in nodulation (29 per cent.) or failed to nodulate any of the four clover hosts (6 per cent.). There were initially only about 5 clover rhizobia per gram in the two soils examined but no difficulty was experienced in obtaining growth of bacteria in sterilized soil or successful inoculation of seed of subterranean clover sown in unsterilized soil in pots. A pure culture of each of the five strains was capable of forming nodules, but strains 297 and 298 were responsible for most of the nodules produced from a mixed inoculum. While the relative success of the strains in producing nodules appeared to be independent of their rate of multiplication in sterilized soil, it was affected to some extent by the type of soil.