Distribution and diversity of rhizobia nodulating agroforestry legumes in soils from three continents in the tropics

Authors

  • Abdullah Bala,

    1. Imperial College at Wye, University of London, Wye, Ashford, Kent TN25 5AH, UK,
    2. Department of Soil Science, Federal University of Technology, PMB 65, Minna, Nigeria,
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  • Phillip Murphy,

    1. Imperial College at Wye, University of London, Wye, Ashford, Kent TN25 5AH, UK,
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    • §

      Present address: Molecular and Immunogenetics Group, Institute of Liver Studies, Kings College Hospital, Denmark Hill, London SE5 9RS, UK.

  • Ken E. Giller

    Corresponding author
    1. Imperial College at Wye, University of London, Wye, Ashford, Kent TN25 5AH, UK,
    2. Plant Production Systems, Department of Plant Sciences, Wageningen University, PO Box 430, 6700 AK Wageningen, the Netherlands
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K. E. Giller. Fax: + 31 317484892; E-mail: Ken.Giller@wur.nl

Abstract

The natural rhizobial populations of Calliandra calothyrsus, Gliricidia sepium, Leucaena leucocephala and Sesbania sesban were assessed in soils from nine sites across tropical areas of three continents. The rhizobial population size varied from undetectable numbers to 1.8 × 104 cells/g of soil depending on the trap host and the soil. Calliandra calothyrsus was the most promiscuous legume, nodulating in eight soils, while S. sesban nodulated in only one of the soils. Polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analyses of the 16S rRNA gene and the internally transcribed spacer (ITS) region between the 16S and 23S rRNA genes were used to assess the diversity and relative abundance of rhizobia trapped from seven of the soils by C. calothyrsus, G. sepium and L. leucocephala. Representatives of the 16S rRNA RFLP groups were also subjected to sequence analysis of the first 950 base pairs of the 16S rRNA gene. Eighty ITS groups were obtained, with none of the ITS types being sampled in more than one soil. RFLP analysis of the 16S rRNA yielded 23 ‘species’ groups distributed among the Rhizobium, Mesorhizobium, Sinorhizobium and Agrobacterium branches of the rhizobial phylogenetic tree. The phylogeny of the isolates was independent of the site or host of isolation, with different rhizobial groups associated with each host across the soils from widely separated geographical regions. Although rhizobial populations in soils sampled from the centre of diversity of the host legumes were the most genetically diverse, soil acidity was highly correlated with the diversity of ITS types. Our results support the hypothesis that the success of these tree legumes in soils throughout the tropics is the result of their relative promiscuity (permissiveness) allowing nodulation with diverse indigenous rhizobial types.

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