First report of Fusarium culmorum and Fusarium avenaceum causing vascular necrosis in European hazelnut branches in Chile.

Abstract

Hazelnut (Corylus avellana L.) is the second most cultivated nut crop in Chile. Pathogens associated with fungal trunk diseases (FTD) pose a serious threat to this crop, because these fungi colonize the wood causing loss of productivity and eventually death of the plants (Martino et al., 2025). During Spring 2018 and 2020, FTD symptoms such as wood necrosis, vascular discoloration of branches, cankers, and wilted branches were detected in a survey conducted in 24 hazelnut orchards located between Maule and Araucanía regions, Chile (Moya-Elizondo et al., 2023). Wood pieces (3 mm x 5 mm) were removed from the edge of necrotic canker lesions, disinfected with 2% NaOCl, rinsed twice with sterile distilled water, and dried on sterile absorbent paper. Tissue pieces were placed on potato dextrose agar (PDA) supplemented with streptomycin sulphate (200 mg L⁻¹) and incubated at 25°C in darkness for five days. Different fungi were isolated from cankers, but based on morphological characteristics (pale pink or burgundy colonies), Fusarium spp. were identified in 5.2% of the samples (27/520). Each colony was hyphal-tip purified in a new PDA plate. Macroconidia developed on sporodochia after 30 days of incubation at 25°C on carnation leaf agar. Two morphologically different isolates were analyzed. Colonies of isolate F066 were cottony, dark pink and light pink on the edges when grown on PDA. Macroconidia were hyaline, falcate with rounded apical cells, slightly curved, with 3 to 6 septa (30 to 53 x 5.2 to 6.2 µm). Isolate F094 presented slightly cottony colonies, light pink, and dark pink with pale yellow hues in the central area with macroconidia of similar morphological shape but measuring 36 to 55 x 2.8 to 4.2 µm. In both isolates, chlamydospores and microconidia were absent. The ITS, RPB2, and TEF-1α genomic regions were amplified with primers ITS1/ITS4, 7cf/11ar, and EF1/EF2, respectively (Sandoval-Denis et al., 2018). The ITS (MT640271, PP928999), RPB2 (MT997139, PP934182), and TEF-1α (MT661593, PP934183) sequences were deposited in GenBank, showing 100% similarity with reference sequences of Fusarium culmorum (Wm.G.Sm.) Sacc. and Fusarium avenaceum (Corda) Sacc. for ITS: (MK729631, MT463390), RPB2 (GQ915490, MK185027), and TEF-1α (MN044434, KP400709), respectively. To fulfil Koch's postulates, pathogenicity was evaluated in 8-year-old hazelnut plants cv. Tonda di Giffoni in a commercial orchard. A hole of 6.5 mm in diameter was made in healthy branches using an electric drill and an actively growing mycelial disc (5 mm) was placed into five branches per isolate, ensuring contact of the mycelium with the wood. The wounds were sealed with plastic film to prevent contamination and desiccation. Additionally, PDA discs were inoculated as a control. After seven months, branches were cut longitudinally to verify wood necrosis. Inoculation with isolates F066 and F094 resulted in necrotic lesions ranging between 50-125 mm and 30-80 mm in length, respectively. No necrosis was observed with the control inoculations. Small wood pieces were cut from the advancing necrotic zone, disinfected, and placed on PDA plates and incubated at 25°C as described above. Hyphal tips were taken from mycelia grown from wood pieces and placed on PDA. F. culmorum and F. avenaceum isolates were observed in 100% of the inoculated branches, showing similar mycelial growth and microscopic fungal structures as those observed for the pathogens. To our knowledge, this is the first report of F. culmorum and F. avenaceum affecting hazelnuts plants in Chile and worldwide. Fusarium lateritium had been previously reported in Italy, causing cankers and cambium death in hazelnut twigs (Belisario et al., 2005). The current study reveals a possible host jump and a presumed change in the disease dynamics of these phytopathogens, which primarily cause diseases in cereals (Karlsson et al., 2021).