Identification and characterization of the causal agent of Dutch elm disease in Croatia
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ORIGINAL PAPER
Identification and characterization of the causal agent of Dutch elm disease in Croatia Zorana Katanić1 · Ljiljana Krstin1 · Marin Ježić2 · Bruno Ćaleta1 · Paula Stančin2,4 · Marko Zebec3 · Mirna Ćurković‑Perica2 Received: 7 November 2019 / Revised: 18 February 2020 / Accepted: 27 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Dutch elm disease (DED) is a vascular wilt disease of elms caused by ascomycetous fungi of the genus Ophiostoma. The initial DED pandemic was caused by Ophiostoma ulmi, a relatively weak pathogen when compared to Ophiostoma novoulmi, the causal agent of the current pandemic. The latter has been spreading as two distinct subspecies: O. novo-ulmi ssp. novo-ulmi and O. novo-ulmi ssp. americana. Weak prezygotic barriers to hybridization have resulted in the emergence of ssp. novo-ulmi × ssp. americana hybrids in subspecies overlap zones. In this study, samples of host species Ulmus laevis, Ulmus minor and Ulmus glabra from across Croatia were analysed for DED prevalence and pathogen distribution and characterization. Dutch elm disease was confirmed in all three elm species, but the prevalence of the infection was approximately four times higher in U. minor and U. glabra than in U. laevis. Ophiostoma novo-ulmi was identified as the only cause of DED, while O. ulmi was not detected, indicating complete replacement of O. ulmi by O. novo-ulmi in Croatia. PCR–RFLP analysis and sequencing of the cu and col1 genes indicate the presence of both O. novo-ulmi subspecies as well as their hybrids at investigated sites, often in high frequency. The results provide insight into distribution and population structure of Dutch elm disease pathogen in Croatia, as well as an assessment of virulence for selected isolates, which could be utilized for making informed management decisions regarding DED and elm conservation in Croatian forests. Keywords Ulmus spp. · Ophiostoma novo-ulmi · Subspecies hybridization · Virulence
Introduction Communicated by Claus Bässler. Marko Zebec was formerly at University of Zagreb, Zagreb, Croatia. Zorana Katanić and Ljiljana Krstin have contributed equally to this paper. * Mirna Ćurković‑Perica mirna.curkovic‑[email protected] 1
Department of Biology, Josip Juraj Strossmayer University of Osijek, 31000 Osijek, Croatia
2
Department of Biology, Faculty of Science, University of Zagreb, 10000 Zagreb, Croatia
3
Department of Forest Genetics, Dendrology and Botany, Faculty of Forestry, University of Zagreb (Former Affiliation), 10000 Zagreb, Croatia
4
Department of Biology, Josip Juraj Strossmayer University of Osijek, 31000 Osijek, Croatia
Native elms populations in Europe and North America have been devastated by two pandemics of Dutch elm disease (DED), a vascular wilt disease caused by invasive ascomycetous fungi of the genus Ophiostoma. First DED pandemic was caused by Ophiostoma ulmi (Buisman) Nannf. which spread across Europe, North America and Southwest and Central Asia during the 1920s–1940s, and declining
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