Xanthomonas arboricola pv. fragariae: a confirmation of the pathogenicity of the pathotype strain

Abstract

Xanthomonas arboricola pv. fragariae is the causal agent of strawberry bacterial leaf blight, and, so far, has been reported in Italy and Turkey. Some years later the description of this new pathovar, and its pathogenicity, was questioned based upon artificial inoculations performed with some strains of the pathogen, including the pathotype strain; it was concluded that it is a non-pathogenic xanthomonad. This notion has also been accepted in other studies aiming at elucidating the molecular characteristics of X. arboricola strains. In the present investigation, we performed again pathogenicity tests using the pathotype strain of X. a. pv. fragariae, namely PD 2780 = LMG 19145 = CFBP 6771, by a spray leaf inoculation technique on strawberry cultivars Candonga, Sabrina and Murano. Similarly, it was also inoculated onto pot-cultivated walnut, hazelnut, peach, apple and kiwifruit plants. All typical symptoms of bacterial leaf blight of strawberry were observed within 25 days after the artificial inoculation on all tested strawberry cultivars. None of the other plant species showed symptoms of disease. We conclude again that the pathotype strain of X. a. pv. fragariae is a pathogenic bacterium. This technique also allowed us to observe typical symptoms of strawberry bacterial blight in a shorter time than that obtained previously by puncturing the major vein of the three leaflets of the leaf.