Dieback of apple trees: a complex syndrome and an increasing problem in Northern Italy (Trentino region)

Abstract: Dieback and blight symptoms on apple trees have been increasingly observed inTrentino (Northern Italy). Stunted growth, chlorotic leaves, cracking, necrosis of the bark andcankers appear mainly at the base of the trunk and on the graft union. Affected plants commonlydie during the growing season. To identify agronomic and weather conditions promoting thesyndrome, an extensive monitoring was carried out in the main fruit-growing areas of Trentino.Symptomatic apple trees were sampled and microorganisms colonising the affected tissues wereisolated in order to identify potential causal agents. The highest incidence of the syndrome hasbeen observed on young stressed plants grown in low fertile soils and cold areas with southsoutheastexposure. Bacteria (Pseudomonas syringae) and fungi (Phomopsis spp., Nectria spp.,Botryosphaeriaceae) were isolated from necrosis and cankers. Pathogenicity tests were conductedto confirm their role in the syndrome.