Occurrence of Truncatella angustata causing canker and branch dieback of European hazelnut in the Maule region, Chile

In Chile, the European hazelnut (Corylus avellana L.) is grown commercially on 49,000 ha, with 22,000 ha cultivated in the Maule Region (35°26′S, 71°40′W) under Mediterranean conditions. During October (2024) and January (2025) in two commercial hazelnut orchards in San Clemente (8-yrs-old; 5 ha) and Linares (12-yrs-old; 4 ha), Maule Region containing cv. Tonda Di Giffoni plants, symptoms of canker and dieback were observed with an incidence of 5% to 10%. Symptoms included a general decline, canker and twig death, and branch dieback. Cross-sections of diseased twigs and branches revealed firm, necrotic lesions. Diseased branches (n=10 samples for orchard) were disinfected with 96% ethanol, flamed for 15 s, and internal tissue was placed onto acidified potato dextrose agar (APDA) containing 0.1% Igepal and antibiotics (Díaz and Latorre 2014). After a 7-day incubation period at 20 °C, six isolates (30%) were obtained and purified by transferring hyphal tips to fresh APDA. After 10 days, colonies developed cottony, opaque white to brown mycelium with black acervuli, and a dark brown pigmentation was observed on the reverse side of Petri dishes after 10 days on APDA. Conidia were two-celled, brown to dark brown, thick-walled, with hyaline apical and incomplete basal cells. Conidia (n=50) measured (25–) 21 ±1.4 (–18.3) x (8.4–) 6.4 ± 0.6 (–4.8) µm with a length/width ratio of 3.3 and contained prominent septa. Two to four hyaline apical appendages were observed, variable in size and dichotomously branched; the basal appendage was absent. Fungal identification was further confirmed (Razaghi et al. 2024) using BLAST analysis of bulk sequenced PCR products of the internal transcribed spacer (ITS1-5.8S-ITS2) region (White et al. 1990) and partial beta-tubulin (Bt) (Glass and Donaldson 1995) genes for three representative isolates. The gene sequences of T. angustata isolates A3, A40, and A98 were deposited in GenBank (PV687318 to PV687320 for ITS; PV929978 to PV929980 for Bt) and showed 99% similarity compared to sequences of the T. angustata type specimen CPC 21354. Combined phylogenetic analysis using MEGA7 software and the maximum parsimony test clustered the three isolates with T. angustata CPC 21354. Based on morphological and molecular analysis, the fungus was identified as Truncatella angustata (Pers.) S. Hughes (Sutton 1980; Espinosa et al. 2008; Razaghi et al. 2024). For pathogenicity tests, lignified twigs attached to tree were selected (three isolates; n=180 twigs total; 20-25 cm long; 15 twigs/tree) of hazelnut cv. Tonda Di Giffoni (8 years-old) in San Clemente, Talca. Fresh pruning wounds were inoculated with 40 μL of a 105 conidia/mL suspension. An equal number of twigs (n=45 twigs) were inoculated in a similar manner with sterile water which served as the control. Two months after inoculation, canker lesions at the tip exhibited a length of 15 to 35 mm. No lesions were observed on the control twigs, and re-isolations were negative. T. angustata was consistently reisolated (100%) from inoculated twigs and morphologically and molecularly (gene) identified, thus fulfilling Koch’s postulates. To the best of our knowledge, this is the first report of T. angustata causing canker and dieback of hazelnut in Chile. This pathogen was previously reported to cause twig dieback of blueberry in Chile (Espinoza et al. 2018). This highlights the importance of including T. angustata in diagnostic protocols and disease management strategies for hazelnut cultivation in Chile.