Invasion of European pine stands by a North American forest pathogen and its hybridization with a native interfertile taxon

Abstract

It was recently reported that North American (NA) individuals of the forest pathogen Heterobasidion annosum were found in a single pine stand near Rome, in association with the movement of US troops during World War II. Here, we report on some aspects of the invasion biology of this pathogen in Italian coastal pinewoods, and on its interaction with native (EU) Heterobasidion populations. Spores of Heterobasidion were sampled using woody traps in pine stands along 280 km of coast around Rome. DNA of single-spore colonies was characterized by two sets of nuclear and one set of mitochondrial taxon-specific polymerase chain reaction primers. NA spores were found not only in a single site, but in many locations over a wide geographic area. Invasion occurred at an estimated rate of 1.3 km/year through invasion corridors provided by single trees, and not necessarily by sizable patches of forests. Within the 100-km long range of expansion, the NA taxon was dominant in all pure pine stands. Because abundance of the EU taxon is low and identical among stands within and outside the area invaded by NA individuals, we infer that the exotic population has invaded habitats mostly unoccupied by the native species. Discrepancy between a mitochondrial and a nuclear marker occurred in 3.8% of spores from one site, a mixed oak-pine forest where both taxa were equally represented. Combined phylogenetic analyses on nuclear and mitochondrial loci confirmed these isolates were recombinant. The finding of hybrids indicates that genetic interaction between NA and EU Heterobasidion taxa is occurring as a result of their current sympatry.

Alien fungal species distribution: the study case of Favolaschia calocera

“…Some non-intentional, human-mediated basidiomycete introductions are well known and have been proved (e.g. Coetzee et al 2001;Gonthier et al 2004Gonthier et al , 2007.…”

“…The most common pathways for the introduction of fungal pathogens are the movement of infected planting stock (Coetzee et al 2001;Milgroom and Peever 2003) or infested wood (Brasier 2001). Notorious examples of introduced and invasive plant pathogens include potato blight (Phytophthora infestans, Fry et al 1992Fry et al , 1993Andrivon 1996;Grünwald and Flier 2005), chestnut blight (Cryphonectria parasitica, Heiniger and Rigling 1994;Gryzenhout et al 2006), Dutch elm disease (Ophiostoma ulmi, Gibbs and Wainhouse 1986;Gilbert 2002), white pine blister rust (Cronartium ribicola, Maloy 1997;Sniezko 2006), Armillaria root rot (A. mellea s.s. in SouthAfrica, Coetzee et al 2001), and recently Puccinia distincta, the cause of a devastating rust disease of daisies (Preece et al 2000;Weber et al 2003) and North american strains of Heterobasidion annosum (Gonthier et al 2004(Gonthier et al , 2007.…”

Rapid Detection of Ceratocystis platani Inoculum by Quantitative Real-Time PCR Assay

“…Woody discs were used to catch the conidia of Heterobasidion irregulare in pine plantations (18,19), while paper filters were used to trap the inoculum of Fusarium circinatum in sites infected with pine pitch canker (20). The use of reliable trapping methods, combined with sensitive molecular approaches, such as real-time quantitative PCR (qPCR) assays, allows for rapid and specific detection of fungal pathogens from these samples (21).…”

Environmental Factors Driving the Recovery of Bay Laurels from Phytophthora ramorum Infections: An Application of Numerical Ecology to Citizen Science

“…The interest of forest pathologists in unraveling environmental factors driving plant diseases has been amplified in the last decades by the onset of relevant epidemics caused by emerging pathogens such as Phytophthora ramorum Werres, De Cock and Man in't Veld in Western North America, Heterobasidion irregulare Garbelotto and Otrosina, Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz and Hosoya, and Gnomoniopsis castaneae G. Tamietti in Europe, just to cite a few relevant examples [3][4][5][6][7][8][9][10][11][12]. The main environmental drivers underlying the success of such novel epidemics have often been identified through a numerical ecology approach, based on computational and multivariate statistical techniques suitable to deal with complex ecological datasets [10,11,[13][14][15][16][17][18][19][20][21][22].…”