Abstract
The symbiotic responses of three Asian-type soya bean cultivars were compared with those of three US-type cultivars and of a cowpea cultivar. A total of 59 strains representing four different groups of rhizobia were used: (a) fast-growing Rhizobium japonicum, (b) slow-growing R. japonicum, (c) Rhizobium spp isolated from US- and Asian-type soya beans grown in West Africa, and (d) Rhizobium spp isolated from cowpeas grown in West Africa. The US-type cultivars were effectively nodulated by slow-growing R. japonicum, but with most of the other strains they produced either no nodules or ineffective nodules. The Asian-type soya beans each responded differently to the four groups of rhizobia, and although they produced effective nodules with a majority of the strains, the symbioses were ineffective with significant frequency. The patterns of effectiveness of the West African soya bean rhizobia with the Asian-type soya beans correlated strongly with the location of origin of the strains. The greatest degree of promiscuity and the highest frequency of effective nodulation were found with the cowpea.
