Effect of virulence and serial transfers of Xanthomonas campestris on xanthan gum production

The virulence of six Xanthomonas campestris isolates was evaluated using th e percentage of lesion area of leaves in Brassica oleraceae host plant, com pared to diameter of colonies, xanthan production and gum viscosity. In ter ms of virulence, the isolates belonged to two statistically different group s: isolates B, UPF and C-7 showed values between 52 and 69%, while isolates CF, C and strain B-1459 gave 0-30% of lesion area. Final xanthan concentra tion, gun viscosity and colony diameter did not correlate with virulence ca lculated by percentage of lesion area, showing that this parameter is not a good criterium for selection of potential xanthan producer isolates. Seria l transfers of X campestris is isolates in host plant did not show a signif icant effect on "in vitro" production of xanthan or on viscosity levels, su ggesting that the increasing interaction between plant and bacteria did not stimulate the increase in xanthan production and viscosity.