Isolation of two strains from Prunus persica able to induce plant tumours that showed phosphate solubilization in vitro.

José Luis Palomo¹, Raúl Rivas², Alvaro Peix³, Pedro F. Mateos², Eustoquio Martínez-Molina², Pablo García-Benavides¹ and Encarna Velázquez²

1. Centro Regional de Diagnóstico. Junta de Castilla y León. Salamanca. Spain

2. Departamento de Microbiología y Genética. Universidad de Salamanca. Spain

3. Departamento de Producción Vegetal. IRNA-CSIC. Salamanca. Spain

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Family Rhizobiaceae currently includes nodule inducing bacteria from Sinorhizobium, Rhizobium, Allorhizobium and tumour inducing bacteria from Agrobacterium. Within genus Rhizobium, Rhizobium huautlense, belonging to the phylogenetic group of Rhizobium galegae, showed the higher phosphate solubilization in plates. Within genus Agrobacterium, only the type strain of A. rhizogenes shows a moderate ability to solubilize phosphate. In this work, we have used two strains, 163C and 97/546, able to originate tumours in tomato plants and also able to solubilize bicalcium phosphate in plate. These strains showed a 100% homology with that of type strain of Agrobacterium rhizogenes. Application of LMW RNA profiling to the strains isolated in this study and to Agrobacterium rhizogenes showed that these strains displayed a 5S rRNA zone characteristic of Rhizobium. Phylogenetic trees also showed that type strain of A. rhizogenes clustered with Rhizobium tropici and not with species from genus Agrobacterium. Therefore, the two strains isolated in this study should be included in genus Rhizobium and together with the type strains of Agrobacterium rhizogenes forms a group able to solubilize bicalcium phosphate within the phylogenetic group of Rhizobium leguminosarum.