RESISTANCE OF Xanthomonas arboricola pv. juglandis TO ION COPPER IN WALNUT ORCHARDS IN THE BIOBÍO REGION

Abstract

The walnut blight disease, caused by the bacterium Xanthomonas arboricola pv. juglandis (Xaj) severely affects walnut production in the Biobío Region in Chile. The disease control is based on the excessive use of cupric bactericides (12 to 14 spray applications during the growing season), which can generate resistance by the bacteria. This research evaluated the in vitro bacterial resistance of bacterial strains of Xaj to ion copper (Cu+2) at different concentrations. The strains were obtained from four orchards located in the Biobío Region. Levels of copper resistance were higher than those previously reported in Chile, irrespective of the copper bactericides used (copper sulfate pentahydrate, copper hydroxide, and copper (I) oxide). Sensible isolates of Xaj were observed in three of the four walnut orchards sampled.