New Zealand’s sweet cherry (Prunus avium) industry covers approximately 1150 ha (Statistics New Zealand 2022) and reached a record export value of NZ124 million in the 2024/25 season. Canker diseases are an emerging concern in New Zealand cherry production, with increasing reports of wood-infecting fungi associated with tree decline and mortality. In December 2024, dark circinate perithecia were observed under the bark of approximately 8-10 five-year-old ‘Sentennial’® (SPC103) cherry trees distributed across consecutive rows within a single orchard block in a commercial Upright Fruiting Offshoot (UFO) orchard in Central Otago, New Zealand (-45. 0510, 169. 1700). The fruiting bodies were associated with trunk and branch cankers on wilted or declining trees. Wood sections from active canker margins were surface sterilised in 1% sodium hypochlorite, rinsed in sterile water, cut into 3-5 mm segments, plated onto streptomycin-amended (100 mg/L) potato dextrose agar (PDA) and incubated at 20–22 o C. After 10 days, red-pigmented colonies were consistently observed, and hyphal-tip cultures were prepared; all isolates showed identical morphology. Colonies incubated at 21 o C under black light were slow growing, initially flat and white to pale-yellow, turning orange to pale pink with a white border and reached colony diameters of 11 mm, 14 mm and 72 mm after 7, 10 and 21 days respectively. Mycelium was septate, red- to pink-pigmented; conidiophores short, with hyaline unbranched phialides and monophialidic condiogenous cells (7. 8 to 10. 8 µm x 0. 9 to 1. 9 µm) ; conidia were hyaline, allantoid and aseptate (3. 9 to 5. 8 µm x 0. 9 to 2 µm). These morphological characteristics are consistent with Calosphaeria pulchella (Réblová et al. 2004; Trouillas et al. 2012). Two isolates (ICMP 24078 and CP24/13) were selected for molecular confirmation and were identified by sequencing the internal transcribed spacer (ITS) and ß-tubulin gene (TUB2) regions. Sequences were deposited in GenBank (accession nos. PX022374, PX056650, PX532316, PX548828). BLASTn analysis in GenBank showed 100% identity between the ITS (593/593 nucleotides) and TUB2 (491/491 and 461/461 nucleotides) regions for isolates ICMP 24078 and CP24/13 with the corresponding reference sequences of C. pulchella type strain CBS 115999 (NR₁45357, KT716476). Concatenated phylogenetic analysis grouped ICMP 24078 and CP24/13 with other C. pulchella isolates, forming a well-supported clade. Pathogenicity testing was conducted on living, potted two-year-old cherry (SPC103/Sentennial) plants. On 24 November 2024, a 5-mm wound was created in the bark of the trunk with a cork borer and isolates ICMP 24078 and CP24/13 were each used to inoculate five trees with 5-mm mycelial plugs from 14-day-old cultures; five additional trees received a PDA plug as a control. The inoculated area was sealed with Parafilm® and plants were incubated in a shadehouse in Lincoln (-43. 641, 172. 476), without temperature or humidity control. After 166 days, the length of the vascular necrosis extending from the inoculation site was measured. Isolates ICMP 24078 and CP24/13 produced mean lesion lengths of 62. 5 mm and 50. 0 mm, respectively, both significantly greater than the control mean of 12. 2 mm (ANOVA, Tukey’s HSD, p < 0. 05). Calosphaeria pulchella was successfully re-isolated from all inoculated stems but not from the control plants, fulfilling Koch’s postulates. Calosphaeria canker, caused by C. pulchella, is increasingly recognised as a significant pathogen of sweet cherry and other Prunus species globally (Gramaje et al. 2014; Grinbergs et al. 2023; Trouillas et al. 2024; Mitrev et al. 2025), with an expanding host range and geographic distribution. To our knowledge, this is the first report of C. pulchella from New Zealand, consistent with Réblová et al. (2004) who reported the species only from Europe. Further research and ongoing surveillance are needed to understand its potential impact on the New Zealand cherry industry.
Marroni et al. (Sat,) studied this question.