Inter- and Intra-Continental Genetic Variation in the Generalist Conifer Wood Saprobic Fungus Phlebiopsis gigantea

Abstract

Phlebiopsis gigantea (Fr.) Jülich is a well-known generalist conifer wood saprobe and a biocontrol fungus used in several world countries to prevent stump infection by tree pathogenic Heterobasidion fungal species. Previous studies have reported the presence of regional and continental genetic differentiation in host-specific fungi, but the presence of such differentiation for generalist wood saprobes such as P. gigantea has not been often studied or demonstrated. Additionally, little information exists on the distribution of this fungus in western North America. The main purposes of this study were: (I) to assess the presence of P. gigantea in California, (II) to explore the genetic variability of P. gigantea at the intra and inter-continental levels and (III) to analyze the phylogeographic relationships between American and European populations. Seven loci (nrITS, ML5–ML6, ATP6, RPB1, RPB2, GPD and TEF1-α) from 26 isolates of P. gigantea from coniferous forests in diverse geographic distribution and from different hosts were analyzed in this study together with 45 GenBank sequences. One hundred seventy-four new sequences were generated using either universal or specific primers designed in this study. The mitochondrial ML5–ML6 DNA and ATP6 regions were highly conserved and did not show differences between any of the isolates. Conversely, DNA sequences from the ITS, RPB1, RPB2, GPD and TEF1-α loci were variable among samples. Maximum likelihood analysis of GPD and TEF1-α strongly supported the presences of two different subgroups within the species but without congruence or geographic partition, suggesting the presence of retained ancestral polymorphisms. RPB1 and RPB2 sequences separated European isolates from American ones, while the GPD locus separated western North American samples from eastern North American ones. This study reports the presence of P. gigantea in California for the first time using DNA-based confirmation and identifies two older genetically distinct subspecific groups, as well as three genetically differentiated lineages within the species: one from Europe, one from eastern North America and one from California, with the latter presumably including individuals from the rest of western North America. The genetic differentiation identified here among P. gigantea individuals from coniferous forests from different world regions indicates that European isolates of this fungus should not be used in North America (or vice versa), and, likewise, commercially available eastern North American P. gigantea isolates should not be used in western North America forests. The reported lack of host specificity of P. gigantea was documented by the field survey and further reinforces the need to only use local isolates of this biocontrol fungus, given that genetically distinct exotic genotypes of a broad generalist microbe may easily spread and permanently alter the microbial biodiversity of native forest ecosystems.

Efficacy of Chemical and Biological Stump Treatments for the Control of Heterobasidion occidentale Infection of California Abies concolor

“…However, P. gigantea products, such as the Rotstop ® C formulation (BioFOrest Tehnologies Inc., Sault Ste. Marie, Canada) that is commercially available in the US, are based on an eastern strain of P. gigantea, are genetically distinct from western strains of the same fungus and recent work has argued against deploying them in western US forests [47]. Our study was the first to apply and report the efficacy of California isolates of P. gigantea in terms of preventing H. occidentale establishment or growth on stumps and is thus extremely timely and provides data on a possible future alternative to the commercially available P. gigantea formulation.…”

Host-associated Intraspecific Phenotypic Variation in the Saprobic Fungus Phlebiopsis gigantea

“…stumps [ 20 ]. A recent study identified three genetically differentiated lineages within P. gigantea , one from Europe, one from eastern North America and one from California [ 21 ]. However, there is no information on whether intraspecific variation between sympatric populations of the fungus associated with different hosts may occur.…”

Antagonistic interactions between native fungi of Minnesota and the root rot pathogen Heterobasidion irregulare

“…(Bailey et al., 2003; Holdenrieder & Greig, 1998; Korhonen et al., 1994). In commercial forestry operations, P. gigantea is now widely used in Europe and North America with strains patented as Rotstop® (Dovana et al., 2021; Gonthier & Thor, 2013). The primary mode of action of P. gigantea involves resource competition and the ability to quickly colonize stumps (Holdenrieder & Greig, 1998).…”

“…(Bailey et al, 2003;Holdenrieder & Greig, 1998;Korhonen et al, 1994). In commercial forestry operations, P. gigantea is now widely used in Europe and North America with strains patented as Rotstop® (Dovana et al, 2021;Gonthier & Thor, 2013).…”