First Report of Kernel Dry Rot Caused by Eremothecium coryli on Hazelnut in Northwestern Italy

Italy is one of the largest hazelnut producers in the world behind Turkey (International Nut and Dried Fruit Council 2017). In recent years, hazelnut cultivation has increased vastly owing to good yields, which are the result of the improvement of cultivation techniques. Oversupply is no longer a problem because global consumption has increased owing to chocolate industry demand and for direct consumption in addition to processed uses. Moreover, people are increasingly aware of the health benefits of nuts. In the last 2 years, a survey of Italian hazelnut orchards has been carried out to investigate on the origin of defects of hazelnut kernels. Hazelnut kernel samples of cultivar ‘Tonda Gentile Trilobata’ collected in July 2017 from an orchard close to Vercelli province (northwestern Italy) were almost all damaged by a bug (Rhynchota, Pentatomidae) and had typical dry rot symptoms. The margin of lesions was disinfected in 4% sodium hypochlorite for 90 s, rinsed in sterile water for 60 s, and dried on sterile filter paper in a laminar flow. Tissue fragments were placed onto potato dextrose agar and observed daily for mycelial growth. Numerous colonies with yeast-like morphology were obtained. Oval or spherical budding cells (4.8 ± 2.4 µm) either isolated or in short chains were present. In addition to budding cells, two to eight needle-like ascospores were arranged lengthwise in many cylindrical to naviculate asci (61.8 ± 4.45 × 2.4 µm). Ascospores (on average 69.5 ± 3.1 × 7.3 ± 1.2 µm) had a distinct septum at or near the center, and the upper cell was slightly broader at the septum. After liberation, ascospores were held together in a mass by long appendages. The morphology of the different fungal structures resembled Eremothecium coryli (Peglion) Kurtzman, an insect-transmitted yeast (Kurtzman 1995). Morphological identification was confirmed by molecular sequence comparison with 100% identity with E. coryli (GenBank accession no. KY053846). The primers used in a polymerase chain reaction were ITS1F (Gardes and Bruns 1993) and ITS4 (White et al. 1990). The sequences of three isolates were submitted to GenBank with accession numbers LT990244 to LT990246. The pathogenicity of the three isolates was tested by inoculating the apex of fresh and mature hazelnuts after making a little hole with a sterile needle and introducing 25 μl of 10⁶ ascospores/ml suspension into each kernel cavity. The inoculated nuts (20 replicates for each isolate) and controls treated with sterile water only (10 replicates) were incubated in the dark at 25°C and only for the first 48 h in a humid growth chamber. After 11 days, nutshells were removed and the kernels halved. Necrotic lesions were identical to those initially observed, and reisolations from the margin of lesions gave yeast colonies with the same morphological characters as those used for inoculation, thus confirming Koch’s postulates. To our knowledge this is the first report of E. coryli dry rot in Italy and western Europe in general, which has already reported by Bobev et al. (2018) in Bulgaria. This disease represents a further menace when associated with the invasive and greatly damaging brown marmorated stink bug.