The application of a molecular assay for early detection of European canker (Neonectria ditissima) in apple trees

Abstract: Neonectria ditissima causes European canker and is one of the most important fungal diseases of apple trees in countries with a temperate climate. Significant yield losses can occur through girdling of branches and stems, limiting fruit production, eventually leading to tree death. Infections in the propagation and nursery stages can remain asymptomatic for several years after planting. Early detection of these asymptomatic infections could contribute to prevent further development and spread of European canker at a later stage in the orchards. However, to date no fast methods are available. Recently, a molecular assay was developed for the quantification of N. ditissima in asymptomatic wood tissues. Therefore, the objective of this research was to develop a practical application using the molecular assay for the pre-screening of nursery plant material. Several inoculation experiments were conducted using leaf scars and different concentrations of N. ditissima to gather information necessary for protocol development. The preliminary results presented demonstrate that colonization of N. ditssima can be detected and measured over time and distance up to 30 mm in apple branches and that the measured target DNA concentrations may have predictive power for lesion establishment. The next steps and complexity for implementation of a practical application are discussed. Outcomes of this research may help future research towards detection tools and improved management of European canker.