title: Winter Conditions Correlate with Phytophthora alni Subspecies Distribution in Southern Sweden.
abstract: During the last century, the number of forest pathogen invasions has increased substantially. Environmental variables can play a crucial role in determining the establishment of invasive species. The objective of the present work was to determine the correlation between winter climatic conditions and distribution of two subspecies of the invasive forest pathogen Phytophthora alni: P. alni subspp. alni and uniformis killing black alder (Alnus glutinosa) in southern Sweden. It is known from laboratory experiments that P. alni subsp. alni is more pathogenic than P. alni subsp. uniformis, and that P. alni subsp. alni is sensitive to low temperatures and long frost periods. By studying the distribution of these two subspecies at the northern limit of the host species, we could investigate whether winter conditions can affect the geographical distribution of P. alni subsp. alni spreading northward. Sixteen major river systems of southern Sweden were systematically surveyed and isolations were performed from active cankers. The distribution of the two studied subspecies was highly correlated with winter temperature and duration of periods with heavy frost. While P. alni subsp. uniformis covered the whole range of temperatures of the host, P. alni subsp. alni was recovered in areas subjected to milder winter temperatures and shorter frost periods. Our observations suggest that winter conditions can play an important role in limiting P. alni subsp. alni establishment in cold locations, thus affecting the distribution of the different subspecies of P. alni in boreal regions.
authors.affiliation: First, second, and fourth authors: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7026, 750 07 Uppsala, Sweden; and third author: Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Göteborg, Sweden.
authors.forename: Miguel A
authors.identifier: http://orcid.org/0000-0002-6383-5457
authors.initials: MA
authors.lastname: Redondo
authors.affiliation: First, second, and fourth authors: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7026, 750 07 Uppsala, Sweden; and third author: Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Göteborg, Sweden.
authors.forename: Johanna
authors.initials: J
authors.lastname: Boberg
authors.affiliation: First, second, and fourth authors: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7026, 750 07 Uppsala, Sweden; and third author: Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Göteborg, Sweden.
authors.forename: Christer H B
authors.initials: CH
authors.lastname: Olsson
authors.affiliation: First, second, and fourth authors: Department of Forest Mycology and Plant Pathology, Swedish University of Agricultural Sciences, Box 7026, 750 07 Uppsala, Sweden; and third author: Department of Biological and Environmental Sciences, Gothenburg University, Box 461, 405 30 Göteborg, Sweden.
authors.forename: Jonàs
authors.initials: J
authors.lastname: Oliva
mesh_terms: D029661:Alnus / Q000382:microbiology*; D010838:Phytophthora / Q000254:growth & development*; D010935:Plant Diseases / Q000382:microbiology; D012621:Seasons; D013548:Sweden; D013696:Temperature
keywords: Alnus spp.; Phytophthora plurivora; invasiveness