First report of Cytospora canker caused by Cytospora sorbicola in hazelnut ( Corylus avellana )

Over the past decade, European hazelnut cultivation has expanded rapidly in Chile, exceeding 49,264 ha (ODEPA, 2026). In 2021, symptoms consistent with trunk diseases, including cankers, wood discoloration, dieback, and black pycnidia on cankered tissues were observed in several orchards, mainly in Ñuble Region. Starting in 2020, a survey of symptomatic wood samples (n=396) was conducted in commercial orchards (n=44) of the cultivars ‘Tonda di Giffoni’, ‘Lewis’, ‘Barcelona’, and ‘Yamhill’, from Maule (35°19'34.7"S 71°18'38.7"W) to Los Ríos (39°51'34.2"S 72°43'10.3"W). Symptomatic wood sections (0.5 cm diameter) were disinfected in 10% sodium hypochlorite, incubated on a quarter-strength acidified potato dextrose agar (aPDA1/4) at 25°C, and developing isolates were purified on PDA. Pure cultures showed olivaceous colonies with irregular margins and submersed, velvety mycelia, reaching 90 mm diameter after 8 days at 25°C. Pycnidia (n=10) black, subglobose, unilocular and solitary (2-)1.6 ± 0.2(-1.4) mm, with dark orange-reddish conidial cirri. Conidia (n=50) were hyaline, allantoid and measured (4.3-) 3.8 ± 0.3 (-3.3) x (1.4-) 1.0 ± 0.2 (-0.6) µm, with a length/width ratio of 3.7. Genomic DNA was extracted from two representative isolates for species level identification. The ITS-5.8S, LSU, act, tub2 and tef-1α regions were amplified and sequenced (Muñoz et al. 2024). GenBank accession codes were: PZ342209, PZ366179, PZ451702, PZ411845, PZ417928, for isolate RGM3900, and PZ342210, PZ366180, PZ407653, PZ411846, PZ387797 for RGM3901, respectively. The consensus phylogenetic tree included the concatenated sequences from both isolates and reference Cytospora species belonging to Leucostoma complex (Jiang et al. 2025), based on a maximum-likelihood analysis using the tool IQ-TREE web server. Morphometric and phylogenetic analyses were consistent with Cytospora sorbicola Norphanph., Bulgakov, T. C. Wen &K. D. Hyde (Norphanphoun et al. 2017). Pathogenicity was evaluated on 3 year old potted plants cvs. ‘Lewis’ and ‘Tonda di Giffoni’. Mycelial plugs (0.5 cm) were placed on fresh pruning wounds on the main branches, sealed with plastic film and incubated in a shadehouse for 161 days. Sterile agar plugs were used for controls (n=6). After incubation, branches were longitudinally cut, and the internal discoloration was measured. Symptoms were reproduced in both cultivars, with no statistical differences in discoloration length between isolates or cultivars; however, discoloration was significantly greater in inoculated plants compared to the controls. Moreover, the fungus was successfully reisolated from symptomatic tissues, fulfilling Koch's postulates. To our knowledge, this is the first report of C. sorbicola causing cankers in European hazelnut worldwide; in Chile, the pathogen has been successfully isolated from seven orchards so far, comprising 403 ha of productive area. These findings contribute to a better understanding of the etiology of hazelnut wood diseases. Furthermore, the proximity of hazelnut and sweet cherry orchards should be taken into consideration, as sweet cherry is an important host of C. sorbicola (Li et al., 2024). This highlights the pathogen's ability to infect multiple hosts and suggests that sweet cherry orchards may serve as a source of inoculum for hazelnut, thereby increasing the risk of cross-infections between crops.