Possible entry points of Neonectria ditissima during propagation of apple trees
Abstract: Neonectria ditissima, the cause of European canker, may enter apple trees during propagation. However, when and where the fungus infects during propagation have been subjects for discussion. Both young transplants of rootstocks and rootstocks at a size ready for grafting or T-budding were infected by N. ditissima after artificial inoculation. Among the rootstocks tested, B9 (the second most used rootstock in Norway) was significantly more susceptible than M9, which is the most commonly used apple rootstock in Norway and elsewhere. If budwood was collected from trees with different numbers of lesions with European canker, higher lesion numbers on the mother-trees gave more infected trees following grafting or T-budding than if budwood was collected from trees with fewer or no lesions. Our experiments showed that rootstocks may become infected by N. ditissima through various wound sites during propagation and that contaminated scion wood may host the pathogen.