A Species-Specific PCR Differentiates Two Causal Agents of Hazel Powdery Mildew and Reveals the Occurrence of Erysiphe corylacearum

Abstract

The demand for common hazel (Corylus avellana) fruit increases constantly. Powdery mildew (PM) on hazels in Hungary and throughout Europe was previously caused mainly by Phyllactinia guttata. However, less than a decade ago, another fungus of Asian origin, Erysiphe corylacearum, appeared on hazels in Europe, including Hungary. Our investigation aimed to develop a species-specific PCR (ssPCR) to aid the identification of P. guttata and E. corylacearum, and to assess the presence of the latter, non-native fungus in Hungary. For this study, 59 samples were collected from Hungary between 2021 and 2023. The chasmothecial morphology of the PM fungi was observed, and the internal transcribed spacer (ITS) of ribosomal DNA was sequenced in representative samples. Morphological analysis distinguished two types of chasmothecia. Parts of the chasmothecia, typical of P. guttata, were flattened and spherical with bristle-like appendages, while other chasmothecia, characteristic of E. corylacearum, were distinctly smaller, bearing appendages with branched apices. Sequence data also verified the presence of P. guttata and E. corylacearum in our samples. The developed ssPCR revealed that E. corylacearum was present in more than three-quarters of the samples, more than a quarter of the samples contained both fungi and about one-fifth carried solely P. guttata. The alien fungus E. corylacearum was found in all but one of the sampled regions and was found on C. avellana and also on C. colurna. Erysiphe corylacearum spreads rapidly and can be considered an invasive pathogen. Its practical importance lies in its ability to infect hazelnuts, potentially causing economic losses. Our ssPCR ensures accurate and quick identification of the fungus, which is essential for effective plant protection.