Abstract
Dothistroma septosporum is a haploid fungal pathogen that causes a serious needle blight disease of pines, particularly as an invasive alien species on Pinus radiata in the Southern Hemisphere. During the course of the last two decades, the pathogen has also incited unexpected epidemics on native and non-native pine hosts in the Northern Hemisphere. Although the biology and ecology of the pathogen has been well documented, there is a distinct lack of knowledge regarding its movement or genetic diversity in many of the countries where it is found. In this study we determined the global population diversity and structure of 458 isolates of D. septosporum from 14 countries on six continents using microsatellite markers. Populations of the pathogen in the Northern Hemisphere, where pines are native, displayed high genetic diversities and included both mating types. Most of the populations from Europe showed evidence for random mating, little population differentiation and gene flow between countries. Populations in North America (USA) and Asia (Bhutan) were genetically distinct but migration between these continents and Europe was evident. In the Southern Hemisphere, the population structure and diversity of D. septosporum reflected the anthropogenic history of the introduction and establishment of plantation forestry, particularly with Pinus radiata. Three introductory lineages in the Southern Hemisphere were observed. Countries in Africa, that have had the longest history of pine introductions, displayed the greatest diversity in the pathogen population, indicating multiple introductions. More recent introductions have occurred separately in South America and Australasia where the pathogen population is currently reproducing clonally due to the presence of only one mating type.
Highlights
Biological invaders are plants, animals, invertebrates, or microorganisms that have become established in a new area and that threaten, or have a detrimental effect on the biodiversity and ecology of the new environment (Pimentel et al 2000; Sakai et al 2001; Allendorf and Lundquist 2003; Anderson et al 2004)
Two well-known examples of devastation caused by introduced pathogens on native trees in natural forests include Chestnut blight caused by Cryphonectria parasitica in North America and Europe (Anagnostakis 1987; Heininger and Rigling 1994) and Dutch elm disease caused by Ophiostoma ulmi and O. novo-ulmi in Europe and North America (Brasier 1991)
Ecology and Evolution published by John Wiley & Sons Ltd
Summary
Biological invaders are plants, animals, invertebrates, or microorganisms that have become established in a new area and that threaten, or have a detrimental effect on the biodiversity and ecology of the new environment (Pimentel et al 2000; Sakai et al 2001; Allendorf and Lundquist 2003; Anderson et al 2004). It is well recognized that biological invasions by fungal plant pathogens have had huge impacts on natural and managed forest ecosystems as well as plantation forests (Elton 1958; Desprez-Loustau et al 2007). The ascomycete fungus, Dothistroma septosporum (teleomorph: Mycosphaerella pini), that causes Dothistroma needle blight (DNB), is by far the most important invasive pathogen of non-native pine species (Gibson 1972; Ivory 1987; Bradshaw 2004; Barnes et al 2008a). This disease results in successive needle defoliation, a reduction a 2014 The Authors.
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