Isolation and characterization of tumorigenic bacteria associated with crown gall disease of Prunus humilis Bunge in China

Prunus humilis Bunge ( Cerasus humilis (Bunge) S. ya. Sokolov) (Rosaceae) is a small shrub native to China, highly valued for environmental protection and as a functional food. However, with the increasing scale of cultivation, crown gall disease has become a major concern. In this study, we aimed to isolate and identify the pathogenic strains causing crown gall disease in P. humilis , and investigate their physiological, phylogenetic, opine type, and biological control characteristics. We isolated 45 pathogenic strains from five regions of China. Using phenotypic and phylogenetic analysis of the 16S rRNA gene, we identified 12 strains as Rhizobium rhizogenes and 33 strains as members of the Agrobacterium tumefaciens species complex. Multi-locus sequence analysis of three housekeeping genes ( rpoB , atpD , and recA ) revealed that 11 strains belonged to A. fabacearum and 22 strains belonged to A. radiobacter within the A. tumefaciens species complex. Of the isolated strains, five displayed characteristics identical to the typical nopaline-type Ti plasmid, whereas the remaining 40 strains did not contain nopaline, octopine, or agropine plasmids. However, all strains possessed the trans-zeatin synthesizing gene and agrocinopine synthetase gene, with some also containing nopaline catabolism genes, suggesting the presence of a plasmid closely related to the nopaline type. Resistance to the agrocins produced by R. rhizogenes K1026 was observed in all strains. However, in a greenhouse experiment, K1026 demonstrated 100%, 100%, and 25% control efficiency against three P. humilis -derived pathogenic strains, respectively. These findings reveal unique characteristics of the pathogens responsible for crown gall disease in P. humilis .