Characterization and phylogenetic diversity of Allorhizobium vitis isolated from grapevine in Morocco

Early Access: DEC 2019

International audience

English. AIMS: Crown gall, a phytobacteriosis characterized by the formation of tumours on plant roots was observed in recently planted vineyards of the Meknes region (Morocco). The objective of this research was to analyze the diversity of pathogenic agrobacteria isolated from grapevine in Morocco. METHODS AND RESULTS: Eighty-two isolates from 11 affected vineyards were characterized by recA sequencing and were found to belong to A. tumefaciens genomospecies G1, G4 or G7, Rhizobium rhizogenes, and to Allorhizobium vitis. Only the A. vitis isolates appeared to be pathogenic on tomato and MLSA phylogenetic analyses revealed a weak genetic diversity, with the definition of only four genomic groups. Definition of the A. vitis genomic groups correlateds with specific pathogenic traits: indeed, genomic groups differed with respect to the severity of hypersensitive response symptoms on tobacco leaves, the intensity of necrotic response on grapevine explants, and opine profiles. Both vitopine and octopine were detected by UHPLC in tumors induced by isolates of three genomic groups, an opine signature scarcely ever reported. CONCLUSIONS: Allorhizobium vitis is the only causative agent of crown gall on grape in Morocco, pathogenic isolates can be separated into four genomic groups. SIGNIFICANCE AND IMPACT OF THE STUDY: This study of recently crown-gall-infested vineyards demonstrated that Allorhizobium vitis is the only causative agent and revealed the presence of non-pathogenic Agrobacterium strain within tumors. Moreover, as the genetic diversity of the A. vitis isolates is relatively narrow, this study lays the basis for further analyses on the evolution of the disease, on the dissemination of the pTi and more globally on the fate of the different genomic groups in this newly colonized environment.