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Evaluation of the intrinsic competitiveness and saprophytic competence of Rhizobium tropici IIB strains
Authors:K. M. Vlassak  F. Mercante  R. Straliotto  A. Franco  M. Vuylsteke  J. Vanderleyden
Affiliation:(1) F.A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Willem de Croylaan 42, B-3001 Heverlee, Belgium Tel.: (16)322-403; FAX: (16)322-990, BE;(2) CNPAB/EMBRAPA, Itaguai, Rio de Janeiro, Brazil, BR;(3) Universitair Rekencentrum, Katholieke Universiteit Leuven, B-3001 Heverlee, Belgium, BE
Abstract:Inoculation of beans (Phaseolus vulgaris L.) with strains of R. tropici IIB and R. etli resulted in the disappearance of the R. tropici IIB stains from the nodule population and their replacement by other (non R. tropici IIB) bean symbionts (Vlassak et al. 1996). Coinoculation studies in monoxenic conditions and in soil core microcosms with plants harvested at two different growth stages indicated that the inoculated R. tropici IIB strains CIAT899 and F98.5 possess a good intrinsic competitiveness which declines, however, at a later plant growth stage and in soil conditions. The poor saprophytic competence of R. tropici IIB strain CIAT899 was further demonstrated by its poor survival in soil core microcosms after bean harvest. Strains were isolated from the field plots with a 3-year bean-planting history, characterized and evaluated for their competitiveness against R. tropici IIB strain CIAT899. Isolates from field plots, which had been repeatedly inoculated with R. tropici IIB strain CIAT899, showed a higher nodule occupancy compared to R. tropici IIB strain CIAT899, and this higher competitiveness exhibited by the field isolates might be an additional reason for the poor performance of R. tropici IIB strain CIAT899 in the field study. Plots with and without a history of bean production revealed after 3-year bean cultivation an almost totally different population that also significantly differed in competitiveness. Received: 12 February 1996
Keywords:Competitiveness  Genetic exchange  Rhizobium etli  Rhizobium tropici IIB  Saprophytic  competence  Symbiotic nitrogen fixation  Nodule population
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