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First Report of Diaporthe australafricana-Caused Stem Canker and Dieback in European Hazelnut (Corylus avellana L.) in Chile

European hazelnut (Corylus avellana L.) is an emerging crop for export, mainly in southern Chile. Stem cankers and dieback of twigs on six-year-old European hazelnut cultivar Barcelona were observed during the 2012 growing season on plantations in Panguipulli (39° 38′ 37.12″ S and 72° 20′ 10.87″ W), Region de Los Rios, Chile. The incidence has been variable according to the place of plantation; it was estimated at approximately 15%. Cankers were characterized by brownish-gray and brown to reddish discoloration of the vascular stem system. Hazelnut plants between 1 and 3 years old developed stem basal canker, especially at conditions of high humidity and overpopulation of weeds; at critical conditions, the affected plants generally die. Small pieces of cankered stems, selected from 10 European hazelnuts, were surface sterilized in 0.5% sodium hypochlorite for 2 min and rinsed twice in sterile distilled water prior to incubation in a humid chamber for 7 days (25 ± 2°C) to stimulate production of reproductive bodies. Black sub-epidermal perithecia with unitunicate, cylindrical-clavate, 8-spored asci (n = 20) were obtained. Ascospores were septated, hyaline, multigutulate, and slightly constricted at the septum, the average measurements were (n = 20) 13.4 ± 0.6 μm × 3.9 ± 0.2 μm. The ascospores were transferred to potato dextrose agar (PDA) and incubated for 6 days at 25°C in the dark, then hyphal tips were transferred to fresh PDA and obtained a mycelia with white, cottony, and sparse colonies. Pycnidia and smooth, unicellular, hyaline, and biguttulate alpha conidia of 6.1 to 7.2 μm × 2.8 to 3.1 μm (n = 40) were observed. Beta conidia were not observed in culture media. Mature pycnidia were also detected on hazelnut shells remaining on the soil from the previous season. The identification of the species (isolate IMI-501237) was confirmed at CABI, United Kingdom, using an internal transcribed spacer (ITS), rDNA, BLASTn analysis of the 524-bp fragment, and showed 100% identity with Diaporthe australafricana Crous & J.M. van Niekerk (accessions KC343039, KC343038). These molecular and morphological characteristics were similar that reported from Vitis vinifera (2) and Chilean blueberry (3). The sequence obtained was deposited in GenBank (Accession No. JX316218.1). A pathogenicity test was conducted with isolate IMI-501237 on four 1-year-old plants from the hazelnut cultivar Barcelona. Plants were maintained in individual bags in greenhouse conditions (14/10 h dark/light, 20°C; 70% relative humidity). Prior to inoculation, plant tissues were surface disinfected with 2% sodium hypochlorite and rinsed with sterile distilled water. Each plant was inoculated at fresh wound sites on three stems and three vegetative buds on twigs. The inoculum consisted of an agar plug with mycelia (5 mm) from the edge of an actively growing colony cultured on PDA for 6 days. Each inoculation was covered with moistened cotton and sealed with Parafilm; a control plant was inoculated in the same way with agar only. After 30 days, necrotic lesions and discolored vascular tissue were only observed on inoculated stems and twigs. Symptomatic tissues were removed and incubated on PDA. D. australafricana was consistently recovered from these tissues, satisfying Koch's postulates. The control plant showed no symptoms of the disease. D. australafricana were previously reported on Vitis vinifera in Australia and South Africa (2,4), and Vaccinium corymbosum in Chile (1,3). To our knowledge, this is the first report of Diaporthe australafricana on Corylus avellana cultivar Barcelona in worldwide.

References: (1) K. Elfar et al. Plant Dis. 97:1042, 2013. (2) R. Gomes et al. Persoonia 31:1, 2013. (3) B. Latorre et al. Plant Dis. 96:5, 2012. (4) J. M. van Niekerk et al. Australas. Plant Pathol. 34:27, 2005.