Abstract

The interest in hazelnut (Corylus avellana L.) cultivation has recently increased in Hungary, it is currently grown on 490 hectares. In August 2021 early powdery mildew symptoms were observed in a hazelnut plantation, and in a variety collection of the Hungarian University of Agricultural and Life Sciences in Érd. White patches of mycelium and conidia were observed on both side of the leaves. In early October abundant chasmothecia were formed. The disease incidence was 100% on varieties 'Segorbe', and 'Corabel', 70% on 'Ennis', and 30% on the leaves of 'Istrska dolgoplodna leska' (15 plants per cultivar). Powdery mildew is usually caused by Phyllactinia guttata, which was present abundantly on the abaxial and sparsely on the adaxial surface of the observed leaves. However, another fungus co-occurred on the adaxial surface of the leaves, and rarely occurred on the abaxial surface of the leaves. Its morphology differed substantially from P. guttata on having smaller chasmothecia, and branched appendages. The new powdery mildew agent was morphologically described. Mycelium was hyaline, branched, septate, thin-walled and smooth, 2.5-3.1 μm wide. Conidiophores measured 22 to 61 × 5.1 to 8.5 (average: 44.1 × 6.5) μm (n = 30), the foot cells were erect, cylindrical, and flexuous. Conidia occurred rarely and were produced single on conidiophores, 19 to 34 × 15 to 24 μm. Chasmothecia were spherical, 74 to 103 (average: 85) μm in diameter (n = 100), single or in groups on both sides of each leaf. Appendages 7 to 15 per chasmothecium, aseptate, straight, sometimes flexuous with a length of 74 to 118 (average: 103) μm (n = 50), and had 3 to 5 times dichotomous branched apices with curved tips. Each chasmothecium contained 3 to 5 asci. Ovoid to subglobose asci measured 43 to 65 × 32 to 54 μm (average: 56 × 43) μm (n = 30). Asci contained 4 to 8 ascospores which were hyaline, ellipsoid, measured 17 to 23 × 11 to 20 (mean: 21 × 15) μm (n = 40) in diameter. Morphological identification was confirmed by molecular analysis of two samples, one from the plantation, and one from the variety collection. After DNA extraction partial rDNA internal transcribed spacer region (ITS) of the isolates was amplified using primers ITS1_F and ITS4_R, as previously indicated (Meparishvili et al. 2019). Obtained sequences were deposited to the GenBank (accession no. OL744964 and OL744961). BLAST analysis indicated that the two samples were showing 100% and 97,81% identity to ITS rDNA sequences of Erysiphe corylacearum from Switzerland (MN822722), and showed low similarity of 83% and 85% each to P. guttata (AB080558). Pathogenicity tests were accomplished on ten healthy two-year-old plants of C. avellana cv. 'Merveille de Bollwiller' with the two isolates under controlled environment on 25°C, 80% humidity and 16/8 photoperiod. Plants were artificially inoculated by conidial suspension droplets (104/ml). Symptoms appeared after 7-8 days after inoculation and the developing fungus was morphologically identical to the original isolates. Control plants were treated with distilled water, no symptoms were found on them. E. corylacearum was first observed on C. avellana in Turkey in 2013 (Sezer et al. 2017) and was considered as a highly destructive pathogen. It is also known in neighbouring countries, Ukraine (Heluta et al, 2019), Austria (Voglmayr et al. 2020) and Romania (Rosati et al. 2021). To our knowledge, this is the first report of Erysiphe corylacearum in Hungary.

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