Diversity of Rhizobia Nodulating Phaseolus vulgaris L. in Two Kenyan Soils with Contrasting pHs

Abstract

Rhizobia were isolated from two Kenyan soils with pHs of 4.5 and 6.8 and characterized on the basis of their host ranges for nodulation and nitrogen fixation, colony morphologies, restriction fragment fingerprints, and hybridization with a nifH probe. The populations of rhizobia nodulating Phaseolus vulgaris in the two soils were similar in numbers and in effectiveness of N 2 fixation but were markedly different in composition. The population in the Naivasha soil (pH 6.8) was dominated by isolates specific in host range for nodulation to P. vulgaris; these all had multiple copies, in most cases four, of the structural nitrogenase gene nifH. Only one of the isolates from this soil formed effective nodules on Leucaena leucocephala, and this isolate had only a single copy of nifH. By contrast, the population in the acid Daka-ini soil (pH 4.5) was composed largely of broadhost-range isolates which had single copies of nifH. The isolates from the Daka-ini soil which were specific to P. vulgaris generally had three copies of nifH, although one isolate had only two copies. These rhizobial isolates are indigenous to Kenyan soils and yet have marked similarities to previously described Rhizobium species from other continents.

Symbiotic specificity of tropical tree rhizobia for host legumes

“…P. vulgaris was promiscuous for both nodulation and N 2 fixation, while C. pubescens was apparently promiscuous for nodulation, but specific in effectiveness, and V. unguiculata behaved in a manner intermediate between these two. P. vulgaris is reputed to be highly promiscuous with fast-growing rhizobia, and does not effectively nodulate with slow-growing rhizobia (Bromfield & Barran, 1990;Anyango et al, 1995;Michiels et al, 1998). On the other hand, V. unguiculata is the most promiscuous legume studied to date, and nodulates with a wide range of both fast-and slowgrowing rhizobia (Trinick, 1980;Allen & Allen, 1981;Lewin et al, 1987).…”

“…strain NGR234 (Trinick, 1980;Lewin et al, 1987;Krishnan & Pueppke, 1994). M. atropurpureum, which is considered to have a broad host range (Gibson et al, 1982;Thies et al, 1991), and known to nodulate with both fast-and slow-growing rhizobia (Trinick, 1968(Trinick, , 1980Lewin et al, 1987;Anyango et al, 1995) nodulated only with the control strains. Thus, its host range appears to be more restricted, at least with respect to the strains used in this study, than species such as F. albida, T.…”

Identification at the species and symbiovar levels of strains nodulating Phaseolus vulgaris in saline soils of the Marrakech region (Morocco) and analysis of the otsA gene putatively involved in osmotolerance

“…Other American species, R. tropici and R. leucaenae (formerly R. tropici type A), nodulating P. vulgaris could have also been transported by bean seeds to Europe and Africa. In Africa, strains identified as R. etli, R. tropici and R. gallicum have been found in common bean nodules [4,5,10,26,31,35], some of them isolated in Morocco from soils affected by salinity. High concentrations of sodium chloride in soils is an increasing problem which significantly limits the crop production in arid and semi-arid areas [61], particularly when nitrogen nutrition is provided by symbiotic nitrogen fixation [11,18].…”

Different species and symbiotic genotypes of field rhizobia can nodulate Phaseolus vulgaris in Tunisian soils

“…R. tropici predominated in acid soils from France [20] and Kenya [16], but was scarcely represented in African populations from neutral soils [15,16], and in Mexican and Argentinean populations [19,21]. R. leguminosarum was most prevalent in European soils [20,22^24].…”