Apiognomonia erythrostoma: an emerging disease of stone fruits in Italy
Abstract: Apiognomonia erythrostoma is a fungal pathogen of stone fruits known as the causal agent of cherry leaf scorch. In the Emilia-Romagna region the disease has been reported since 2001 on apricot, and severe infections have been recorded on sweet cherry trees since 2013. In 2015, symptoms resembling those made by A. erythrostoma were observed on sweet cherry in a mountainous area in the Trentino region. Symptoms on the leaves start with pale green spots that turn yellow and red, while affected areas become necrotic and the leaves dry up, remaining attached to the tree. Irregular red areas appear on the fruit, causing deformity and cracks. In Emilia-Romagna, a preliminary epidemiological study on apricot was carried out in the field over three years, with the aim of determining infection events. Dead, overwintered leaves containing fruiting bodies of A. erythrostoma were collected from apricot trees and investigated for ascospore maturation. Maturation and release of ascospores was correlated with degree days and compared with infections in the field. This preliminary investigation provided information about the first, maximum peak and end of ascospore release. Monitoring of the presence of the disease in Emilia-Romagna and Trentino was carried out in the main apricot and cherry growing areas. Typical symptoms on leaves, fruit and the reproductive structures of A. erythrostoma were found both in orchards and on wild cherry trees in the surrounding areas, suggesting that infected uncultivated trees may act as an inoculum source for the pathogen. In 2016, preliminary epidemiological studies of perithecial maturation, ascospore release and symptom development on potted plants were also carried out in Trentino. Potted cherry plants were exposed to ascospore infection from infected cherry leaf litter. Ascospore release was monitored by means of a volumetric spore trap placed over the leaf litter. Potted cherry plants were exposed and replaced weekly with healthy ones. The first ascospores were detected by the spore trap during the first ten days of April, with a peak at the end of May, in conjunction with rain. Symptoms on leaves appeared four to six weeks after the infection event. Further studies will be necessary to fully understand the biology and the epidemiology of this fungus in northern Italy, in order to implement an effective control strategy.