Interaction between Xanthomonas citri pv. viticola and its alternative natural host, Senna obtusifolia, and species in the family Amaranthaceae

Alternative hosts play an important role on the survival of plant pathogenic bacteria. They represent sources of inoculum for new infections; therefore, the identification of potential alternative hosts and the study of their interaction with plant pathogens are essential for the development of effective disease management strategies. The objective of this study was to investigate the interaction between Xanthomonas citri pv. viticola (Xcv), the grapevine bacterial canker (GBC) pathogen, and its alternative host, Senna obtusifolia, and species in the family Amaranthaceae (Amaranthus spinosus, A. cruentus, Chenopodium giganteum, and C. quinoa), for a better understanding of the host range of this pathogen and epidemiology of GBC. Pathogenicity tests showed that all species developed symptoms after inoculation of Xcv. The dynamics of the leaf population was evaluated up to 20 days after inoculation (DAI). In all plant species, it was observed an increase of the total population of Xcv after inoculation. Xcv also showed the ability to survive epiphytically in high populations in S. obtusifolia leaves, after 20 DAI. The ability to invade plant tissues systemically was evaluated by stem inoculation and subsequent detection by specific BIO-PCR. In S. obtusifolia, acropetal and basipetal movement was evaluated by collecting stem fragments at 1, 5, 10, and 15 cm from the inoculation site (IS) at 14 and 20 DAI. In Amaranthaceae plants, only the acropetal translocation was evaluated at 5 cm from IS at 21 DAI. Xcv movement in S. obtusifolia was detected in both directions, at 15 and 10 cm, above and below the IS, respectively. In plants of the family Amaranthaceae, the pathogen was detected in all tissue samples evaluated. The results indicated that Xcv colonized systemically all plant species evaluated and could potentially infect a wider host range than previously known.