The American forest pathogen Heterobasidion irregulare colonizes unexpected habitats after its introduction in Italy

Abstract

Habitat preference of an invasive fungal tree pathogen is here compared with that of a sympatric and native closely related congener to test the hypothesis that the invasive ability of the exotic organism may be linked to its capacity to colonize substrates unavailable to the indigenous relative. We compared the distribution of infectious airspora of the North American Heterobasidion irregulare introduced into Italy with that of the native H. annosum, both regarded to be able to establish only in the presence of conifers. Geostatistical and statistical analyses were employed to test for association between both species and five Mediterranean vegetation types. Results show that H. annosum is positively associated with pines and negatively associated with deciduous oaks. The probability of finding its spores decreases to almost 0 at distances over 500 m from pines, and this species is virtually absent in pure oak forests. Spores of H. irregulare are present irrespective of vegetation type, and this species can be found not only where pines are present, but also in pure oak forests. This knowledge implies that spread of H. irregulare is not limited by the fragmented distribution of pine woodlands in central Italy and is essential to both predict and hinder its progress in Europe.

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

“…Models predicting spread rates of emerging pathogens in forest ecosystems are on the rise, as documented in the last few years for Heterobasidion irregulare and Gnomoniopsis castaneae, just to cite two relevant examples other than P. ramorum [11,16,18,19,108]. Notwithstanding this increased effort, unraveling factors favorable to recovery may help to improve the modelling of disease dynamics and the prediction of related economic losses, as well as to plan more effective mitigation strategies under different climatic or geographic scenarios.…”

“…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].…”

Biotic Factors Affecting Ecosystem Services in Urban and Peri-Urban Forests in Italy: The Role of Introduced and Impending Pathogens and Pests

“…sensu lato), the agent behind "root rot and decay in conifers", have prompted a great deal of concern. This basidiomycete was reported in 2004 on stone pines (Pinus pinea L.) in Castel Porziano-Rome (Latitude 41 • 44 00 N-Longitude 12 • 24 00 E) [46]. It is suspected that it was accidentally introduced by the US Army during the Second World War with weapons crates made of infected pine wood.…”

Heterobasidion annosum s.l. Genomics

“…Also, the native species is strongly associated with certain vegetation types, namely, P. pinea stands, and equally strongly disfavoured by deciduous oak forests. H. irregulare, on the other hand, is not restricted to any Italian vegetative type and thrives equally well in oak forests and pine stands (Gonthier et al, 2012).…”

“…However, in 2006, H. irregulare could be found 24 km NW and 79 km SE from Castelporziano (Gonthier, Nicolotti, Linzer, Guglielmo, & Garbelotto, 2007), indicating that the fungus was widespread already in 2004 or, less likely, that the spread between 2004 and 2006 was very rapid. Evidence suggests that it is not spreading through competition with the native H. annosum s.s. population in this area, but rather by being able to sporulate and disperse in a xeric region, traditionally not well suited for colonisation by the European Heterobasidion species (Gonthier, Lione, Giordano, & Garbelotto, 2012). This might have ecological reasons, while both deposition rates of spores and infection frequency decline significantly for H. annosum s.s. during the dry summer months, the invasive H. irregulare seems to maintain the same propagule pressure throughout the year (Garbelotto, Linzer, Nicolotti, & Gonthier, 2010).…”