Epidemiological studies on Xanthomonas arboricola pv. pruni
In Italy, Xanthomonas arboricola pv. pruni (EPPO A2 quarantine pest) has caused severe outbreaks with heavy losses on plum (Prunus domestica) and peach (P. persica), in the Po Valley and north-eastern areas. In the fruit-growing areas of the Po Valley, it has been observed that summer cankers on plum trees provide important overwintering sites and sources of inoculum for 2 to 3 years on peaches. However in other regions, severe outbreaks have been observed even in the absence of this summer canker phase. It is noted that in France, where the disease has recently been found (see EPPO RS 97/112), cankers are also rarely seen. Therefore, studies were carried in two peach orchards near Verona on the overwintering of X. arboricola pv. pruni in infected fallen leaves, terminal and axillary buds and leaf scars. Survival of the bacterium in the field was studied by using resistant mutants (to antibiotics), inoculated to branches, buds, and leaf scars of peach trees (P. persica cv. Elegant lady). This survival was assessed by periodic reisolation onto appropriate growing medium from plant samples (buds/leaf scars) and from debris of infected leaves present on the soil. Results showed that the bacterium can be recovered from infected fallen leaves, buds and leaf scars, up to 6-7 months after contamination. In these fields, no cankers were observed during summer. The authors concluded that buds, leaf scars and infected leaf debris on the soil can provide overwintering sites and potential sources of inoculum for primary infections
Sources
Zaccardelli, M.; Malaguti, S.; Bazzi, C. (1998) Biological and epidemiological aspects of Xanthomonas arboricola pv. pruni on peach in Italy.
Journal of Plant Pathology, 80(2), 125-132.