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Phyllosphere colonization strategies related to successful infection in Xanthomonas vesicatoria

Ana Romero: Facultad de Agronomia, University of Buenos Aires

<div>Bacterial spot, induced by <em>Xanthomonas vesicatoria</em>, is a serious constrain of field grown tomatoes in Argentina. To better understand strains aggressiveness, several characteristics of three local strains that induce different levels of disease were evaluated. For each strain, we determined <em>in vitro</em> swarming and twitching motilities, biofilm formation, xanthan production and xanthan viscosity. All assays were performed in triplicate. We also evaluated the number and size of the lesions induced by each strain and bacterial multiplication <em>in planta</em>; in both cases we used four plants per strain. Strain BNM208 was the most aggressive: it induced more and bigger lesions than BNM216; BNM214 showed intermediate values. When inoculated by infiltration, avoiding the need for phyllosphere colonization, all strains reached similar population sizes. Among the strains evaluated, BNM208 presented the greatest swarming and twitching motilities. BNM 208 also developed a mature biofilm with presence of defined cell clusters, a homogeneous and compact structure, and higher biomass and substratum coverage than BNM214 and BNM216. The three strains produced similar amounts of xanthan, however, BNM208 produced the most viscous polysaccharide, which possibly relates to the better characteristics of its biofilm. The ability of BNM208 to move over surfaces and form mature biofilms may allow a better colonization of the phyllosphere, resulting in a high infection success of this strain.</div>