Abstract：Celery (Apium graveolens) is one of the most consumed leaf vegetables worldwide. With the rapid expansion of the cultivation area of greenhouse vegetables in recent years, the year-round production, continuous cropping, etc. lead to the deterioration of the environment which may cause the emergence of new features of plant disease. In this study, a strain QC02 was be isolated from the celery rotted samples of Changping district in 2015. Based on the analysis of morphology, physiology and biochemistry, the 16S rDNA sequence as well as the average nucleotide identity (ANI) of the genome sequence, a comprehensive identification for QC02 was conducted. The results showed that the QC02 colonies on KB medium were milky white, circular, smooth in surface with even edges, and produced fluorescent pigment under the UV light, and produced pits on CVP (cavity formation on crystal violet pectate) medium. By artificial inoculation, the strain could infect celery and cause stalk rot symptoms, which were similar to those in the fields. The bacterium could also infect potato (Solanum tuberosum), carrot (Daucus carota), garlic (Allium sativum), and onion (Allium cepa). The PCR amplification with Pseudomonas-specific primers Ps-F/Ps-R produced the targeted fragment from QC02 and the Pseudomonas spp. The LOPAT characteristics of this bacterium were in accordance with those of the previously reported Pseudomonas marginalis. Biolog test also identified QC02 as P. marginalis. Among the 13 Pseudomonas type strains whose entire 16S rDNA gene sequence had the over 99% similarity with that of QC02 (GenBank No. MG765472), the characteristic of average nucleotide identity (ANI) based on the whole genome sequence from these strains showed that only the ANI values between QC02 and P. marginalis ICMP 3553T were as high as 98.46%, which was higher than the threshold value (95%) between intra- and inter-species. These results revealed that the strain QC02 causing bacterial rot disease on celery is P. marginalis. This study is the first report about the occurrence of Pseudomonas marginalis on celery in China, and provides a foundation for the disease control measures as well as celery breeding for disease resistance.
