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Poster: Diseases of Plants: New & Emerging Diseases


Survey on pathogenic Xanthomonas recovered from different lettuce cultivars in Canada.
V. TOUSSAINT (1), D. Xu (1), P. Hébert (1), M. Cadieux (1), M. Ciotola (1), H. Van der Heyden (2), D. Rekika (3), S. Jenni (1) (1) Agriculture and Agri-Food Canada, Canada; (2) Compagnie de recherche Phytodata, Canada; (3) Fondation pour l'amélioration gé

Bacterial leaf spot, caused by X. hortorum pv. vitians (Xhv), is an important lettuce disease. In Canada, the main difficulty for disease control is the absence of registered chemicals. Thus, the most sustainable way to reduce yield losses is using resistant cultivars. Preliminary studies showed that different isolates did not share the same lettuce host range. Therefore, different X. hortorum pathotypes should be considered in a breeding program for resistance. The objective was to determine which pathotypes are present in Canada by sampling diseased lettuce plants in commercial production. In 2014 and 2015, 376 lettuce samples were collected in the main lettuce production area. Xanthomonas isolates were recovered from leaf lesions and characterized based on DNA sequences of four housekeeping genes (dnaK, fyuA, gyrB and rpoD). Concatenated DNA sequences of these genes for the isolates and reference strains were analyzed with Neighbor-Joining method using MEGA v6.04 to generate a phylogenetic tree. The 363 isolates formed two major clusters. Cluster I includes 17 strains representing 358 isolates and grouped with the Xhv reference strain BS3046. This Cluster can be separated into two sub-groups and preliminary evidence shows that they shared different lettuce host range. The Cluster II, a distinct group of X. hortorum, contains eight new strains, but the pathotype has to be determined. Further investigation is needed on the epidemiology of this unknown pathotype.