Xanthomonas vesicatoria virulence factors involved in early stages of bacterial spot development in tomato

Abstract

Xanthomonas vesicatoria (Xv) is a member of a species complex that causes bacterial spot on tomato, one of the most important diseases of this crop worldwide. The objective of this investigation was to analyse several characteristics involved in Xv virulence in relation to strain aggressiveness. Motility, biofilm formation, adhesion and production of xanthan were evaluated in three local strains causing tomato bacterial spot in Argentina. The strains assayed presented differential swarming and twitching motilities, adhesion and biofilm formation abilities. The most aggressive strain, BNM 208, exhibited the greatest swarming and twitching motilities, and developed a mature biofilm with presence of defined cell clusters, a homogeneous and compact structure, and higher biomass and substratum coverage than the other two strains. Even though the three strains produced similar amounts of xanthan, BNM 208 produced the most viscous exopolysaccharide, which possibly relates to the better characteristics of its biofilm. Despite other differences, the three strains multiplied to similar levels when they were infiltrated into the leaf. The results suggest that the aggressiveness of Xv strains studied in this work was related to their ability to move by flagella or type IV pili, adhere to leaves and form well developed biofilms, factors that improve phyllosphere colonization. A better understanding of the factors involved in the Xv infection process at the early stages would contribute to developing new control strategies for this phytopathogen.