Abstract
Stumps play a pivotal role in the epidemiology of the fungal forest pathogens Heterobasidion spp. because they are the main courts of primary airborne infections. The aims of this study were (i) to determine the susceptibility of seven tree species (i.e., Larix sibirica, Picea abies, Picea sitchensis, Pinus contorta, Pinus strobus, Pinus sylvestris and Pseudotsuga menziesii) to primary infection by H. annosum and H. parviporum through comparative inoculation experiments of conidia on wood discs in controlled conditions; (ii) to compare the susceptibility of wood discs of the same tree species to natural airborne infections in two Latvian Norway spruce forest stands infested either by H. annosum or H. parviporum; (iii) to explore the rates of infection of wood discs at increasing distances from spore sources in these two forests to make inferences on the range of spores dispersal. Results obtained by spraying wood discs with conidial suspensions in controlled conditions are in agreement with those obtained by exposing wood discs to the natural airborne inoculum in the forests, as clearly supported by the significant correlation (r = 0.79; p < 0.05) between the two sets of data. Susceptibility was highest in Pinus species, followed by P. abies and P. sitchensis. Susceptibility was lowest for L. sibirica and P. menziesii. The area colonized by Heterobasidion spp. in the sapwood of wood discs was much greater than that colonized in the heartwood. A sharp decrease in the rate of infection of wood discs with distance from spore sources (i.e., fruiting bodies) was observed, further confirming the importance of local spore sources in the epidemiology of Heterobasidion spp. Taken together, these findings could help designing tactics to manage these fungal forest pathogens.
Highlights
Heterobasidion is a genus of basidiomycetes in the family of Bondarzewiaceae, including several species, two of which, i.e., H. annosum (Fr.) Bref. and H. insulare (Murrill) Ryvarden, have been reported to be species complexes [1]
Our data shows variation in susceptibility of wood discs of different tree species to primary infection by H. annosum s.l., and, in this regard, results obtained by exposing discs to airborne infections in the forest are fully consistent with those of artificial inoculations in controlled conditions using conidial suspensions
In comparative inoculation experiments on wood discs in controlled conditions using conidial suspensions, larger surfaces were colonized by H. annosum s.l. on wood discs of P. sylvestris, P. strobus and P. abies, and smaller in wood discs of P. menziesii
Summary
Heterobasidion is a genus of basidiomycetes in the family of Bondarzewiaceae, including several species, two of which, i.e., H. annosum (Fr.) Bref. and H. insulare (Murrill) Ryvarden, have been reported to be species complexes [1]. While most Heterobasidion are saprotrophs, those included in the H. annosum species complex, hereafter referred to as H. annosum sensu lato (s.l.), are pathogenic and may be damaging, especially in managed coniferous stands [1,2]. Within H. annosum s.l., three native species occur in Europe: H. abietinum, H. annosum sensu stricto (s.s.), hereafter referred to as H. annosum, and H. parviporum. While the former is found mainly in central and southern Europe in association with its main host, silver fir (Abies alba Mill.), H. annosum and H. parviporum are more widespread throughout Europe, including the Baltic States [2,3,4]. Heterobasidion annosum and H. parviporum display different host preferences: H. parviporum mainly infects Norway spruce (Picea abies (L.) H. The North American invasive H. irregulare has been reported in Italy on Italian stone pine (Pinus pinea L.) [8,9,10]
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