Leaf spot disease on wild cherry (Prunus avium L.) was frequently observed in plantations for timber production in central Italy. Acervuli and conidia of Phloeosporella (= Cylindrosporium) padi (Lib.) Arx were detected. Since the presence in Italy of its teleomorph, Blumeriella jaapii (Rehm) Arx (1), has never been reported, the life cycle of the pathogen was investigated. In the autumn of 1996, in some diseased leaves in different locations, microconidia were observed in the same acervuli that produced macroconidia. Also, in a plantation near Rome, fallen leaves with dark, stromatic spots were present. Leaf samples were put into plastic net bags and laid onto the ground under the trees, to be observed after overwintering in the field. In March, fully developed apothecia were present on the lower leaf surface, containing asci and ascospores that matched the description of B. jaapii. To verify the capability of the ascospores produced in nature to infect the host, overwintered leaf fragments with mature apothecia were fixed to the underside of the lids of petri dishes, above healthy cherry leaves laid upside down on moistened filter paper. Uninoculated, healthy leaves kept in petri dishes served as control. Dishes were incubated at room light and temperature conditions. The ascospores were readily discharged and dark spots with hypophyllous or amphigenous acervuli of P. padi developed on infected leaves 20 days later. No symptoms were present in the control leaves. In conclusion, B. jaapii can complete its life cycle in wild cherries in Italy. The possibility of spring infection by ascospores should be considered in disease management programs.
Reference: (1) S. Kaszonyi. Acta Phytopathol. Acad. Sci. Hung. 1:93, 1966.
