Detached shoot treatments cannot replace whole-tree assays when phenotyping for apple resistance to Neonectria ditissima
To develop a fast phenotyping method for European canker resistance of apple, detached-shoot assays were compared with whole-tree phenotyping methods. Disease incidence and lesion length in detached shoots and potted trees of six apple accessions were compared after inoculation with Neonectria ditissima conidia in a glasshouse. Detached shoots were placed in aerated water or in a Chrysal solution, with and without water changes. ‘Royal Gala’ trees had the highest disease incidence (90%) and ‘Robusta 5’ trees remained lesion-free. The treatment-accession interaction effect was significant, with higher disease incidence in detached shoots of ‘Robusta 5’ (4—32%) than ‘Braeburn’ (0—2%), while ‘Braeburn’ trees had a high disease incidence (64%). ‘Robusta 5’ had smaller lesions than the other accessions, but significant differences between accessions were observed on only one of three assessment dates. None of the detached-shoot assays resulted in a similar ranking of the accessions compared with the potted-tree assay, using disease incidence or lesion length. Detached-shoot treatments cannot replace whole-tree assays when phenotyping for European canker resistance of apple.