Characterization of Agrobacterium rubi in roses in Brazil

The agribusiness of flowers and ornamental plants has been consolidating in Brazil. A study was carried out to investigate the cause of rose galls observed in the state of Goiás. The galls were quantified, eradicated, and re-quantified. Bacterial isolations were carried out, followed by determination of physiological characteristics and pathogenicity. Molecular identification was performed using Agrobacterium-specific PCR primers (23S and VirC), sequencing of the 16S rDNA and gyrB genes, in conjunction with phylogenetic analysis. In a plot with approximately 300 plants, 971 galls were removed and counted, indicating a high disease incidence of 3.2 galls per plant. Nonetheless, the galls on the plants reappeared at an incidence of 2.1 galls per plant. The samples recovered from infected plants were Gram-negative and oxidase-negative, catalase-positive, aerobic, grew on NGA medium supplemented with 2% NaCl at 35ºC, did not produce fluorescent pigment or 3-ketolactose, and clarified acid on potato dextrose agar containing 0.5% CaCO₃. In pathogenicity tests, only habanero pepper and carrot did not exhibit gall symptoms. A 1006 base pair (bp) fragment specific to the Agrobacterium tumefaciens species complex (23S) and a 414 bp fragment of the virC pathogenicity gene were amplified from DNA obtained from isolates. Phylogenetic analysis based on 16S rDNA and gyrB sequences revealed that the isolate from rose galls clustered with A. rubi reference sequences. To our knowledge, this is the first report of this bacterium in Brazil.