Canker and dieback diseases pose significant threats to cherry production worldwide. During a study assessing canker lesions in a commercial cherry (Prunus avium) orchard in Central Otago, New Zealand, fungal fruiting bodies were observed on symptomatic trees. Laboratory analysis led to the isolation and identification of Calosphaeria pulchella, the first recorded detection of this pathogen in New Zealand.
Symptomatic trees of the cultivar ‘Sentennial®’, established in 2019 and grown under the Upright Fruiting Offshoot (UFO) system, exhibited active cankers with circinate groups of perithecia under the bark. Wood samples collected in April 2024 were surface sterilised, plated onto potato dextrose agar, and incubated at room temperature. Distinctive, red-pigmented mycelium and conidia were observed in culture. Sequence analysis of the internal transcribed spacer (ITS) region showed 100% sequence identity to reference strains of C. pulchella in GenBank (KJ396346, NR_145357). The Ministry for Primary Industries (MPI) validated this identification by also analysing the beta-tubulin (TUB2) gene region and carried out a site visit which determined that the pathogen was present throughout the orchard, also infecting other cherry varieties.
Calosphaeria pulchella is a known canker pathogen of stone fruit, including cherries, peaches, and almonds, with recent reports of severe infections in the USA (California), Chile, and multiple countries in Europe (Italy, Spain, Germany, Czech Republic). It produces ascospores that are dispersed by rain and wind and can infect trees through pruning wounds. The source of the infection in the orchard is unknown. Calosphaeria pulchella is likely to have been present in the Otago region for a long time and may also have spread to parts of the North Island through plant material exchange from another infected plant nursery. The investigation by MPI concluded that eradication is technically and economically unfeasible because of the organism's likely historical introduction, cryptic nature, multiple pathways of spread (including air and water), and the lack of effective management tools.
This study highlights the importance of proactive disease monitoring in commercial orchards and underscores the need for further research on the pathogenicity, epidemiology, and potential control measures for C. pulchella in New Zealand. Investigations are currently underway to fulfil Koch’s postulates and assess the geographic distribution of C. pulchella in New Zealand. If its pathogenicity is confirmed, further research will aim to understand the disease cycle in local conditions and evaluate management strategies, including pruning hygiene, fungicidal treatments, and biological control options.