First Report of Bacterial Wilting Caused by <i>Curtobacterium flaccumfaciens</i> pv. <i>flaccumfaciens</i> on Tobacco

Tobacco (Nicotiana tabacum) is an economically important crop, possessing a multifaceted impact on a global scale. In July 2024, wilting symptoms resembling tobacco bacterial wilt were observed on the cultivar Yunyan87 in a tobacco field (106°05'7.1″E, 26°03'9.9″N), Anshun, Guizhou, China. The infected plants initially presented chlorotic spots on the basal part of the stem, followed by wilting of leaves or stems, vascular browning, and in some cases, even death. Disease incidence is about 40%, causing yield losses over 20%. The disease samples were subjected to a moisturizing treatment overnight at room temperature. Cultured sap obtained from excised stems was diluted with sterilized water and plated onto LB agar plates. Post-incubation at 28°C for 2 days, the buff, circular, smooth colonies were picked from the plates and amplified using colony PCR with reference primers (Gonçalves et al., 2019; Osdaghi et al., 2024; Weisburg et al., 1991). The 16S rDNA sequence data (GenBank accessions PV104305 to PV104307) of three isolates (14-28-27, 14-15-19, and 15-11-17) shared 100% similarity with that of Curtobacterium faccumfaciens type strain C-S-R1-2 (GenBank accession no. MK398100) based on BLASTn search. The phylogenetic tree constructed using MEGA-X version 10.1.6 (Kumar et al., 2018) based on the recA, gyrB, atpD, ppk, and rpoB genes demonstrated that the three isolates belong to C. flaccumfaciens pv. flaccumfaciens (Cfpf). The partial sequences of the five genes were submitted to GenBank with accession numbers PV259359 to PV259373. Pathogenicity test was conducted on 55-day-old tobacco plants grown in plastic pots (8.7 cm height, 9.7 cm upper diameter, and 6.7 cm bottom diameter). Plants were inoculated as described (Urrea, et al., 2014). The plants treated with sterilized water acted as a control. The inoculated seedlings were moved to the greenhouse at 29 ± 1°C and ≥ 60% humidity. Ten days after inoculation, wilting of lower leaves and xylem discoloration were observed in inoculated plants. No symptoms appeared in the controls. Pathogenicity tests were performed three times with consistent results. The bacteria were reisolated from the inoculated plants and identified as Cfpf through colony morphology and multilocus sequence analysis of the recA, gyrB, atpD, ppk, and rpoB genes, fulfilling Koch's postulates. Cfpf, a common plant pathogen, causes the bacterial disease in Dendrobium officinale and Phaseolus vulgaris (Wang et al., 2016; Osdaghi et al., 2020). To our knowledge, this is the first report of Cfpf causing bacterial wilt in tobacco. This report broadens the host range of Cfpf and underscores the significance of this bacterium as a plant pathogen.