Bacterial leaf spot (BLS) of lettuce, caused by Xanthomonas hortorum pv. vitians (Xhv), is a major disease limiting lettuce production worldwide, particularly in tropical environments such as the Everglades Agricultural Area (EAA) in Florida. The pathogen is highly aggressive, rapidly dispersing under favorable conditions, and its sporadic outbreaks make disease prediction and management challenging. While Xhv is primarily known to infect lettuce (Lactuca sativa L.), its potential to colonize alternative hosts, including crops and weeds in lettuce-growing regions, remains poorly understood. This study aimed to evaluate the host range and epiphytic capabilities of Xhv by inoculating two isolates (‘L7’ and ‘SC8B’) onto common leafy vegetable crops and weeds frequently found in or around lettuce fields. A total of 26 plant species were tested, including weeds from Malvaceae (n=1), Portulacaceae (n=1), Amaranthaceae (n=2), Asteraceae (n=3), Brassicaceae (n=1), and Poaceae (n=1), along with vegetable crops from Asteraceae (n=6), Brassicaceae (n=7), and Apiaceae (n=5). Disease severity was assessed 12 days post-inoculation (DPI) using a 0–5 rating scale based on symptomatic foliage area. Initial water-soaked lesions were observed on susceptible lettuce (‘Okeechobee’) at 2 DPI, progressing to necrotic lesions and severe infection with an average disease severity score of 4 at 12 DPI. Notably, symptomatic responses were also observed in endive (Cichorium endivia L.), escarole (C. endivia var. latifolium), and coriander (Coriandrum sativum L.), with median disease severity scores of 3, 3, and 2, respectively. Symptoms in these crops were consistent with BLS in lettuce, including water soaking, chlorosis, and necrosis. In contrast, Brassicaceae species and all tested weeds remained asymptomatic. Bacterial isolations from symptomatic and asymptomatic leaves revealed colonies morphologically consistent with Xhv, displaying yellow pigmentation on nutrient agar. To confirm pathogenicity, hypersensitivity and compatibility response assays were conducted by infiltrating recovered bacterial isolates into resistant (‘PI 358001-1') and susceptible (‘Okeechobee’) lettuce cultivars. Typical disease symptoms developed on susceptible lettuce, confirming Koch’s postulates. The asymptomatic nature of weed species suggests they may serve as reservoirs, potentially contributing to pathogen persistence and dissemination in lettuce fields. These findings provide new insights into Xhv epidemiology and highlight alternative host species that may play a role in disease outbreaks. Understanding the pathogen’s ecological interactions is critical for developing effective disease management strategies and mitigating economic losses in lettuce production systems.
