Agrobacterium pusense, a new plant tumour‐inducing pathogen isolated from Lawson cypress

Lawson cypress (Chamaecyparis lawsoniana), an important landscape tree, is widely planted in gardens and parks throughout Iran. Crown gall disease on Lawson cypress trees was observed in Sari and Juybar Counties, Mazandaran province, northern Iran, in 2017. Isolation from galls on potato dextrose agar (PDA) containing CaCO3 yielded bacterial colonies, the predominant types of which were purified and selected for characterization. The isolates were Gram‐negative, oxidase positive, able to grow in 2% NaCl and produced 3‐ketolactose. They hydrolysed esculin, casein and arbutin but not starch, gelatin or Tween 80. Two representative isolates were selected for PCR amplification and sequencing of DNA gyrase subunit B (gyrB) gene. In the phylogenetic tree based on the partial sequence of the gyrB gene, isolates KH1 and KH2 clustered with Agrobacterium pusense. The pathogenicity of all isolates was confirmed by inoculation on Jimsonweed (Datura stramonium) and carrot discs (Daucus carota). Confirmation of the presence of genes involved in pathogenicity was made by performing PCR with the virD2A/virD2C and VCF/VCR primer pairs which resulted in amplification of the expected 224 and 730 bp fragments in all studied isolates, respectively. A. pusense was therefore identified as the causal agent of crown and stem gall of Lawson cypress. This appears to be the first report on the natural occurrence of crown gall disease on Lawson cypress and the first record of a plant disease caused by A. pusense.