SCREENING FOR PARTIAL RESISTANCE TO FRUIT TREE CANKER IN APPLE CULTIVARS

Fruit tree canker in apple, caused by the fungus Neonectria ditissima, is considered as a serious economic problem in apple orchards, especially in northwestern Europe. This fungus produces cankers on the wood of branches and trunks, and severe attacks can result in the loss of limbs or whole trees. The fungus produces conidia and ascospores, both of which are dispersed and cause infection during prolonged periods of rainy weather. Apple cultivars show variable levels of partial resistance to the fungus, whereas complete resistance has not yet been reported. Therefore, apple genotypes with high levels of genetically determined resistance should be identified for use in apple breeding. In this study, ten apple cultivars were screened for resistance to N. ditissima. For each cultivar, both potted trees and cut-off shoots in glass bottles were inoculated in a greenhouse. The resulting lesions were measured and disease progression curves were calculated; AUC (area under curve) was used for comparisons of infection severity. Significant differences between cultivars were observed in both experiments. The cultivar ‘Rödluvan’ showed the highest degree of resistance in both experiments, while the most susceptible were ‘Jonathan’(cut shoots) and ‘Åkerö’ (potted trees).