Preferred name: Coniferiporia weirii
Authority: (Murrill) L.W. Zhou & Y.C. Dai
Taxonomic position: Fungi: Basidiomycota: Agaricomycotina: Agaricomycetes: Hymenochaetales: Hymenochaetaceae
Other scientific names: Fomitiporia weirii Murrill, Fuscoporia weirii (Murrill) Aoshima, Inonotus weirii (Murrill) Kotlaba & Pouzar, Phellinidium weirii (Murrill) Y.C. Dai, Phellinus weirii (Murrill) Gilbertson, Poria weirii (Murrill) Murrill
Common names in English: laminated butt rot of conifers, root rot of conifers, yellow ring rot of conifers
view more common names online...
Notes on taxonomy and nomenclature EPPO Categorization: A1 list
EU Categorization: A1 Quarantine pest (Annex II A)
view more categorizations online...
EPPO Code: INONWE

Coniferiporia weirii (before it was split into two species) had long been reported as an aggressive forest pathogen mainly of Pseudotsuga menziesii and Thuja plicata but also of many other conifers (Wang et al., 2022). However, the analysis of Coniferiporia species diversification in association with both biogeography and host plants resulted in distinction of two clades: one containing only C. sulphurascens which infests P. menziesii, Pinus spp., Abies spp. and other conifers; the other comprises C. qilianensis, C. uzbekistanensis, C. weirii, and Coniferiporia sp. (Wang et al., 2022). Regarding C. weirii, it mainly infests T. plicata and Callitropsis nootkatensis which are its major hosts (Hagle, 2009), and both of which are naturally distributed in western North America (Mao et al., 2019; Wang et al., 2022). The fungus was also found on Calocedrus decurrens (Zhou et al., 2016).

In the EPPO region, C. weirii could infect T. plicata, Callitropsis nootkatensis, and Calocedrus decurrens (urban trees) and, possibly, other conifer species.

Host list: Callitropsis nootkatensis, Calocedrus decurrens, Thuja plicata

Each species of Coniferiporia can infest specific coniferous plants and has a specific geographic distribution in the Northern Hemisphere (Zhou et al., 2016). Four geographic origins (i.e., Eastern Eurasia, Central Asia, western North America, and Eastern Europe) were set according to voucher information of Coniferiporia species (Wang et al., 2022). Concerning the identification of C. weirii, the presence of this pathogen was confirmed for specimens from British Columbia (Canada), Idaho, and California (USA) on Thuja plicata and Calocedrus decurrens (Wang et al., 2022). Other specimens from Canada, Russia, Japan, China, and the USA (California, Idaho, and Montana) were identified as C. sulphurascens (Wang et al., 2022). Chinese specimens of C. weirii represent a distinct species that was renamed Coniferiporia qilianense, whereas for Central Asian specimens from Uzbekistan the taxonomic identity was recently clarified, and they were described as C. uzbekistanensis (Wang et al., 2022). The geographic distribution of C. weirii should be reconsidered because most of observations consist of findings of both C. weirii and C. sulphurascens and data are not given specifically for C. weirii and C. sulphurascens (EFSA 2018).

North America: Canada (British Columbia), United States of America (California, Idaho, Washington)

As C. sulphurascens and C. weirii had previously been described as one species and the latest species segregation took place very recently (Zhou et al., 2016; Jeger, 2018; Wang et al., 2022), there is limited information regarding C. weirii. The host ranges of the two pathogens differ and their biology is rather distinctive (Banik et al., 1993; EFSA 2018; Wang et al., 2022). C. weirii occurs in North America and causes laminated root and butt rot mainly in Thuja plicata (Larsen et al., 1994; EFSA 2018; Wang et al., 2022). Decay caused by all Coniferiporia species is considered to be initiated by mycelium from residues of former forest trees because the fungus persists in decaying roots and logs for many years and the pathogen is able to infect healthy trees via contact with roots (Sinclair and Lyon, 2005). C. weirii forms thin, resupinate and perennial (2–3 years) basidiocarps (Hagle, 2009), the latter so far being found only on T. plicata (EFSA, 2018). Basidiocarps of C. weirii form at the base of affected trees, most commonly between buttress roots, however they can occasionally be located up to 6 feet (=183 cm) high (Hagle, 2009). Sporulation occurs in spring and summer (Larsen et al., 1994). Further research is needed on spore infection of wounds (Sinclair and Lyon, 2005).

Symptoms

Most of the symptoms were described for C. sulphurascens on P. menziesii, so there is a lack of detailed information on symptoms of C. weirii infection. The fungus can cause laminated root rot in a few conifer species, mainly T. plicata. Following the first signs of C. weirii infection (Murill, 1914), infected trees show reduced growth, thin, chlorotic, and asymmetric foliage and sometimes smaller cones than normal. The pathogen usually affects a group of trees in patches that enlarge over several years (Sinclair and Lyon, 2005). Many trees in the adjacent stand will be infected but will not show crown symptoms for some time. Wind-throw of living trees is common, even before crown symptoms are discernible (Murill, 1914; Hagle, 2009). Young, infected trees often die before disease expansion. In advanced stages, the wood breaks down in a yellow, laminated, pitted rot (Murill, 1914). Brown, crust-like basidiocarps with a broad to narrow, white to cream sterile margin may form on the underside of decayed stems and roots (Hagle, 2009; Zhou et al., 2016). The early stage of decay may be seen as a crescent-shaped/spherical reddish brown to chocolate brown stain in the outer heartwood. Wood in the late stage of decay is yellowish and tends to laminate over the annual ring with many tiny cavities 0.5 x 1.0 mm (Sinclair and Lyon, 2005). Infected trees are frequently attacked by bark beetles and pathogens such as blue-stain fungi or Armillaria species (Sinclair and Lyon, 2005). Wounds and patches where the bark has detached may provide entry points for spores and may also increase the decay in already infected trees due to increased aeration (Hagle, 2009; Hansen et al., 2018). For additional information for C. weirii (Phellinus weirii) see Sinclair and Lyon (2005).

Morphology

Observation with a hand lens will reveal abundant, characteristically long, superficial, reddish brown setal hyphae, 5–10 µm in diameter and up to 3 mm long, with a thickened wall (1.5–2.5 µm) between the sheets of decayed wood. Mycelium lacks clamp connections (Sinclair and Lyon, 2005; EFSA, 2018).

Basidiospores are globose becoming oblong-ellipsoid, with a small apiculus, smooth and hyaline; 3.7–4.5 x 2.9–3.7 µm (Zhou et al., 2016).

Detection and inspection methods

In areas where C. weirii is already present, isolated disease foci in extensive forests can be detected by aerial photography (Wallis and Lee, 1984).

A polymerase chain reaction (PCR) test based on the internal transcribed spacer (ITS) regions can be used to identify species from the C. sulphurascens/weirii complex. PCR tests with specific primers make it possible to distinguish the different species within the complex (Zhao et al., 2016; Wang et al., 2022).

Natural dispersal by spores is considered significant only over short distances (Sinclair and Lyon, 2005; Wang et al., 2022). Long-distance movement is possible, most likely by transportation of infected coniferous logs or bark. Spore infection of wounds has not been adequately studied and the role of basidiospores in disease spread has not been confirmed (Sinclair and Lyon, 2005). Nearly all infections in forest stands with trees of the same age are considered to be initiated by mycelium which survived in roots, butts, logs etc. remaining in the forest for decades and which penetrates into new trees through intact or injured bark (Sinclair and Lyon, 2005).

Economic impact

In North America, C. weirii causes root and butt rot of T. plicata and Callitropsis nootkatensis which are widely spread and highly valued species that have economic and cultural significance (McMurtrey et al., 2023). C. weirii causes a heart rot, affecting all infested trees between 6 years and rotation age, causing root decay leading to direct mortality or accelerated wind-throw. T. plicata is the most susceptible as a seedling and sapling, then becomes more resistant to root disease infections over time (McMurtrey et al., 2023).

Control

Control of C. weirii is rather difficult. Treatment would need to focus on the stumps of harvested trees, where the fungus can persist for decades (Sinclair and Lyon, 2005). These stumps provide one of the main sources of inoculum for the spread of the fungus through root contacts. Therefore, to reduce overall losses from C. weirii root rot, foresters need to identify and to remove infested stumps when feasible. Slash burning will not significantly reduce the level of inoculum in the soil. However, planting of resistant and less susceptible species around infected material (inoculum) with a buffer zone planted with a deciduous species can control the disease successfully (Wallis, 1976; Sturrock et al., 2010).

Phytosanitary risk

The phytosanitary risk posed by C. weirii is low (Sturrock et al., 2010). As spores are probably of minor importance in spreading the infection, the disease occurs in patches which originate, for the most part, when healthy roots contact the fungus (mycelium) in roots and stumps of the previous stand (Wallis 1976). The fungus grows for only a short distance through soil; consequently, spread from tree to tree occurs only where a healthy and diseased root touch each other or when they grow in close proximity (Wallis 1976; Sinclair and Lyon, 2005). Within the EPPO region, establishment of the fungus is unlikely but if happens it may lead to economic and ecological losses of Calocedrus decurrens, Callitropsis nootkatensis, and Thuja plicata which are reported as major hosts in North America (Wang et al., 2022). Other conifers, such as Abies spp. and several other conifers in the family Pinaceae are resistant to C. weirii, but susceptible to C. sulphurascens (Zhao et al., 2016; Wang et al., 2022).

It should be noted that the phytosanitary measures outlined below refer to both C. sulphurascens and C. weirii because they were proposed before the species was split into new species with different biogeography and hosts. 

The main phytosanitary measures recommended by EPPO are listed in the Standard PM 8/2 (3) Coniferae for C. weirii (EPPO, 2018). Import of plants for planting (except seeds) and cut branches of Coniferae originating in countries where C. weirii is present is allowed only from pest-free areas (EPPO, 2018). Import of wood of Coniferae (except Cryptomeria and Taxus) originating in countries where C. weirii is present is allowed only from pest-free areas for C. weirii, or after heat-treatment according to EPPO Standard PM 10/6 (EPPO, 2009), or after appropriate fumigation, details to be specified on the phytosanitary certificate (EPPO, 2018). Import of isolated bark of Coniferae (except Cryptomeria and Taxus) originating in countries where C. weirii is present is allowed only from pest-free area for C. weirii or heat-treated to achieve a minimum temperature of 56°C for a minimum duration of 30 continuous minutes throughout the entire profile of each piece of the bark (EPPO, 2018). Cut branches (including cut Christmas trees without roots or soil) of Abies originating in countries where C. weirii is present is allowed only from pest-free areas for C. weirii (EPPO, 2018). The wood should be inspected for staining and presence of fungal mycelium because roots, wood and stumps infected by C. weirii can serve as viable inoculum sources for decades (Sinclair and Lyon, 2005; EFSA, 2018; Leal et al., 2019).

Banik MT, Paul JA, Burdsall Jr HH, & Cook ME (1993) Serological differentiation of two forms of Phellinus weirii. Mycologia 85(4), 605–611. https://doi.org/10.2307/3760507 

Dai YC (2004) First report of laminated root rot on Sabina przewalskii caused by Phellinus weirii sensu stricto in China. Plant Disease 88(5), 573–573. https:// doi.org/10.1094/PDIS.2004.88.5.573C 

EFSA Panel on Plant Health (2018) Jeger M, Bragard C, Caffier D, Candresse T, Chatzivassiliou E, Dehnen-Schmutz K, Gilioli G, Grégoire J-C, Jaques Miret JA, MacLeod A, Navajas Navarro M, Niere B, Parnell S, Potting R, Rafoss T, Rossi V, Urek G, Van Bruggen A, Van der Werf W, West J, Winter S, Boberg J, Gonthier P & Pautasso M. Pest categorization of Coniferiporia sulphurascens and Coniferiporia weirii. EFSA Journal 16(6), 5302 https://doi.org/10.2903/j.efsa.2018.5302 

EFSA (2019) Baker R, Gilioli G, Behring C, Candiani D, Gogin A & Tramontini S (2019) Report on the methodology applied by EFSA to provide a quantitative assessment of pest‐related criteria required to rank candidate priority pests as defined by Regulation (EU) 2016/2031. EFSA Journal 17(6), e05731. https://doi.org/10.2903/j.efsa.2019.5731

EPPO (2009) EPPO Standards. Phytosanitary Treatments. PM 10/6(1) Heat treatment of wood to control insects and wood-borne nematodes. EPPO Bulletin 39(1), 31. https://doi.org/10.1111/j.1365-2338.2009.02227.x 

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Leal I, Bergeron MJ, Feau N, Tsui CKM, Foord B, Pellow K, Hamelin RC & Sturrock RN (2019) Cryptic speciation in western North America and Eastern Eurasia of the pathogens responsible for laminated root rot. Phytopathology 109(3), 456–468. https://doi.org/10.1094/PHYTO-12-17-0399-R

McMurtrey S, Alcalá-Briseño RI, Showalter D & LeBoldus JM (2023) Draft genome resource for the forest pathogen Coniferiporia weirii – a pathogen of Thuja plicata and Callitropsis nootkatensis. Plant Disease 107(2), 534-537. https://doi.org/10.1094/PDIS-04-22-0917-A

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Wallis GW (1976) Phellinus (Poria) weirii root rot. Detection and management proposals in Douglas-fir stands. Technical Report, Forest Service, Canada No. 12, 16 pp.

Wallis GW & Lee YJ (1984) Detection of root disease in coastal Douglas-fir stands using large scale 70-mm aerial photography. Canadian Journal of Forest Research 14, 523–527. https://doi.org/10.1139/x84-09

Wang X W, Jiang JH, Liu SL Gafforov Y & Zhou LW (2022) Species diversification of the coniferous pathogenic fungal genus Coniferiporia (Hymenochaetales, Basidiomycota) in association with its biogeography and host plants. Phytopathology 112(2), 404–413. https://doi.org/10.1094/PHYTO-05-21-0181-R

This datasheet was extensively revised in 2023 by Kateryna Davydenko, Ukrainian Research Institute of Forestry and Forest Melioration and Swedish University of Agricultural Science. Her valuable contribution is gratefully acknowledged. 

EPPO (2024) Coniferiporia weirii. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-19)

This datasheet was first published in the EPPO Bulletin in 1979 and revised in the two editions of 'Quarantine Pests for Europe' in 1992 and 1997, as well as in 2022. It is now maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.

CABI/EPPO (1992/1997) Quarantine Pests for Europe (1^st and 2^nd edition). CABI, Wallingford (GB).

EPPO (1979) Datasheets on quarantine organisms No.19, Phellinus weirii.  EPPO Bulletin 9(2), 83-87. https://doi.org/10.1111/j.1365-2338.1979.tb02454.x