First Report of <i>Xanthomonas citri</i> pv. <i>viticola</i> causing Bacterial Canker Disease on grapevine in Rio Grande do Norte, Brazil

Grapevine bacterial canker, caused by Xanthomonas citri pv. viticola (Xcv), is considered the most important bacterial disease of Vitis vinifera in tropical viticulture regions of Brazil (Lima et al. 2017). In the state of Rio Grande do Norte (RN), Northeast Brazil, grapevine production is expanding, demonstrating social and economic importance for small farmers, who produced approximately 125 tons of grapes in 2024 (IBGE, 2025). In August 2025, typical symptoms of bacterial canker, i.e., angular necrotic lesions on leaves and cankers on stems (Silva et al. 2020), were observed on 100% of the grapevines (cv. Vitória) in a 7 ha field located in the municipality of Apodi, RN state (05°36'24"S, 37°47'33"W). Samples were collected from a grapevine orchard, and five bacterial strains (CCRMXCV01 to CCRMXCV05) showing whitish, convex, mucoid colonies were isolated in petri dishes containing NYDA medium (Gama et al., 2011), which were incubated at 29°C for 48 h in the dark. The strains were stored at the Culture Collection Rosa Mariano (CCRM) of the Phytobacteriology Laboratory at the Universidade Federal Rural de Pernambuco. Pathogenicity tests were performed on grapevine seedlings (cv. Vitória), 60 days old. The strains were inoculated on the four apical grapevine leaves using a modified gauze-abrasion method (Lima et al. 2017). Briefly, sterile gauze was used to cause light abrasion on the leaf surface, which was sprayed using a bacterial suspension (1 × 10 8 CFU mL -1 ) supplemented with Tween 20 (0.05%) until runoff. The negative control consisted of leaves treated with sterile distilled water (SDW). One leaf was used per replicate, and four replicates were used per strain. Plants were maintained in a humid chamber 24h before and after inoculation, and incubated in the greenhouse, where the average temperature and relative humidity were 31.4ºC±2 and 65%±5, respectively. Inoculated leaves showed symptoms of necrotic lesions on leaves and cankers on veins 14 days after inoculation (DAI). Twenty-five DAI, we reisolated the pathogen and performed a BOX-PCR analysis according to Gama et al. (2018), with the strains inoculated and reisolated on NYDA medium to confirm the identity of the strains and to fulfill Koch’s postulates. At this time, leaves treated with SDW remained symptomless. The strains reisolated showed the same BOX profiles as the strains used for inoculations. The strains showed 100% of similarity and were observed to have five reproducible bands. The molecular identification was performed by sequencing the gyrB (DNA gyrase subunit B) and rpoD (RNA polymerase sigma factor 70) genes according to Young et al. (2008). Using the BLASTn tool, we observed that sequences of the rpoD (PX710105 to PX710109) and gyrB (PX711344 to PX711348) genes of the strains CCRMXCV01 to CCRMXCV05 showed 100% identity with sequences of these genes from the pathotype strain (LMG 965 T ) of Xcv. The phylogenetic analysis performed using Bayesian inference and the gyrB and rpoD concatenated sequence of all the type or representative strains of Xanthomonas spp. available in GenBank showed that the strains CCRMXCV01 to CCRMXCV05 clustered together with strain LMG 965 T , with 1.0 posterior probability. To our knowledge, this is the first report of Xcv causing grapevine bacterial canker in the RN state, Brazil. This finding shows the expansion of this pathogen to yet another Brazilian state, highlighting the importance of pathogen monitoring to prevent further spread to disease-free areas.