Expansion of the Host Range of <i>Xanthomonas euroxanthea</i>: First Occurrence in Sunflower in Bulgaria

Sunflower is a short-season crop of the Asteraceae family and the <i>Helianthus</i> genus and is the fourth most important oilseed crop in the world. During a field campaign, unusual symptoms (necrosis and longitudinal cracking of the petiole) were observed in a sunflower crop grown in the region of Kavarna (Dobrich district, Bulgaria) and strains of the genus <i>Xanthomonas</i> were isolated. Results based on phylogenetic and phylogenomic analyses showed that they clustered with <i>Xanthomonas euroxanthea</i> CPBF 424^T species, a pathogenic strain isolated from walnut buds in Portugal and responsible for causing walnut bacterial blight. The sunflower strain showed five out of eight <i>X. euroxanthea</i>-specific markers (XEA4 to XEA8), a pattern also observed in some strains isolated from <i>Solanum lycopersicum</i>, <i>Phaseolus vulgaris</i>, and rainwater sources, reinforcing the emergence of a recent lineage driven by evolutionary adaptations to new plant hosts. This is the first report of <i>X. euroxanthea</i> in sunflower crops in Bulgaria, which represents a potential threat to production, and its distribution should be monitored.