DIVERSITY AND ADAPTABILITY OF SOYBEAN AND COWPEA RHIZOBIA IN TROPICALSOILS

The current interest on biodiversity, allied with the use of powerful molecular biology techniques, are revealing the nodulation abilities o f tropical legumes, their preferences in terms of relationships with r hizobia, the dynamics of the rhizobia population, and data are accumul ating on the cowpea group of tropical rhizobia. Studies on the ecology of cowpea-nodulating rhizobia in soils from the semi-arid region of B razil, are providing an understanding of the ecology of soybean nodula ting rhizobia in Brazilian soils and are revealing a large community o f native strains capable of nodulating soybeans in soils where soybean s never have been planted. Many isolates showed a limited ability to n odulate soybean roots and formed nodule-like structures, or pseudo-nod ules. Recent host range analysis of known rhizobia species has generat ed substantial data that is rapidly changing recognized patterns of sy mbiotic specificity. Cowpeas, soybeans and common beans nodulate with many different species of rhizobia, and the occurrence of both slow- a nd fast-growing strains in the same plant species has been reported fo r many genera of tropical legumes. This review will focus on recent da ta on the diversity of tropical rhizobia and their adaptability to tro pical soils. Copyright (C) 1996 Elsevier Science Ltd.