Isolation of Agrobacterium tumefaciens/ biovar 1 from the crown gall of Cerasus humilis in China

As an endemic fruit tree in China, the Chinese dwarf cherry (Cerasus humilis (Bge.) Sok.) has substantial ecological and economic value. In 2018, characteristic symptoms of the crown gall of the Chinese dwarf cherry were observed in a nursery base located in Ningxia Hui Autonomous Region, China. The occurrence of the disease among seedlings was observed to be 9.48%. Diseased plants were collected and brought to the laboratory for the isolation of the pathogens. In this study, the isolates were identified by a combination of morphological, biochemical, pathogenicity-related, as well as molecular methods. The isolated strains were white, circular, domed, and glistening. Using 16S rRNA gene sequence analysis and biochemical tests, five strains were identified as Agrobacterium tumefaciens/ biovar 1. Polymerase chain reaction (PCR) was used to detect pathogenicity-associated genes in isolates through the amplification of the partial nucleotide sequences of tms2, virD2 and ipt genes, which proved that the isolates contained the Ti plasmid. In the pathogenicity assay, the crown gall symptom developed on the young stem of tomato and sunflower after inoculation. Based on its morphological, biochemical, pathogenicity and genetic characteristics, the pathogen of the Chinese dwarf cherry crown gall was identified to be A. tumefaciens/ biovar 1.