Eucalyptus occidentalis plantlets are naturally infected by pathogenic Agrobacterium tumefaciens

• Published in: European journal of plant pathology 2006-11, Vol.116 (3), p.237-246
• Main Authors: Krimi, Zoulikha, Raio, Aïda, Petit, Annik, Nesme, Xavier, Dessaux, Yves
• Format: Article
• Language: English
• Subjects: Agrobacterium tumefaciens; Bacteria; bacterial diseases of plants; Bacterial plant pathogens; Biochemistry; Biological and medical sciences; cankers (plants); crown; disease diagnosis; Eucalyptus; Eucalyptus camaldulensis; Eucalyptus occidentalis; forest nurseries; forest trees; Fundamental and applied biological sciences. Psychology; host plants; host range; Life Sciences; Microbiology; nopaline; Phytopathology. Animal pests. Plant and forest protection; plant pathogenic bacteria; polymerase chain reaction; ribosomal RNA; seedlings; strain differences; strains; tree diseases; Vegetal Biology; virulence
• ISSN: 0929-1873; 1573-8469
• DOI: 10.1007/s10658-006-9055-y

In the Sidi M'djahed nursery (Algeria), over 60,000 eucalyptus (Eucalyptus occidentalis) plantlets exhibited tumour-like growths localized at the crown of the plants that resembled crown galls caused by Agrobacterium tumefaciens. Bacteria colonizing the galls were isolated and purified. Most (22 out of 24) of the isolates had cultural and biochemical characteristics similar to those of strains of the biovar 1 of A. tumefaciens. Twenty out of 22 Agrobacterium isolates induced tumour formation on various test plants. In PCR experiments, DNA extracted from these virulent strains yielded an amplification signal corresponding to a 247-bp fragment located within the virulence region of nopaline type Ti plasmid. Consistent with this, the opine nopaline was detected in the tumours induced on test plants - but not on eucalyptus plants. Nopaline was degraded by the 20 pathogenic isolates that were also sensitive to agrocin 84, indicating the presence of a nopaline-type pTi in these strains. The chromosomal region encoding the 16S rRNA was analyzed in a sub-population of the pathogenic agrobacterial isolates. The analyzed strains were found to belong to the ribogroup of the reference strain B6. Interestingly, Eucalyptus camaldulensis and Eucalyptus cladocalyx grown in the same nursery and in the same soil substrate developed no galls.