ANALYSIS OF AGROBACTERIUM POPULATIONS ISOLATED FROM TUNISIAN SOILS: GENETIC STRUCTURE AVIRULENTVIRULENT RATIOS AND CHARACTERIZATION OF TUMORIGENIC STRAINS
M. Bouri, M. Chattaoui, H.B. Gharsa, A. Mcclean, D. Kluepfel, X. Nesme, A. Rhouma
The aim of this work is to assess the presence of agrobacterial populations in a variety of Tunisian soils to provide information regarding the diversity of strains occurring in agricultural soils. Twenty five soil samples were collected from seven different regions, which had or didn’t have a history of crown gall. Agrobacterium spp. members were dominant in Tunisian soils, isolated from 23 samples and assigned to the genomospecies G4, G7 and G9 by specific primers. The majority of samples yielded strains belonging to more than one genomospecies and showed a predominance of G4 and/or G7 members. Partial recA gene sequencing revealed new alleles and a high allelic diversity at both local and country scales. BOX-PCR fingerprinting of non-tumorigenic strains from dominant alleles did not show a clear correlation with geographic origin/soil plantation type, or a clear clonal spread of Agrobacterium strains in Tunisian soils. Ti plasmid-containing strains were only recovered from soils of fields with evidence of crown gall disease, and were exclusively allocated to the genomospecies G4. Tumorigenic strains isolated from soils with galled grapevines were distinct from tumorigenic strains isolated from soils with galled stone fruit trees, based on recA sequences, Ti plasmid type, sensitivity to the strain K84 and L-tartrate utilization.