Annosus root and butt rot (Heterobasidion irregulare)

Fruiting bodies at the base of a tree André Carpentier

French disease name: Maladie du rond (Heterobasidion irregulare)
Pathogen name: Heterobasidion irregulare (Underw.) Garbel. & Otrosina
Kingdom: Fungi
Phylum: Basidiomycota
Class: Agaricomycetes
Order: Russulales
Family: Bondarzewiaceae
Partial list of synonyms:
- Fomes annosus (Fr.:Fr.) Cooke
- Fomitopsis annosa (Fr.:Fr.) P. Karst.
- Heterobasidion annosum (Fr.:Fr.) Bref., groupe nord-américain d’incompatibilité P
- Spiniger meineckellum (A. Olson) Stalpers

Distribution

Canada

Damage, symptoms and biology

The disease causes root rot, which can kill young trees quickly and very large trees after a few years. The infection begins in autumn when the spores germinate on the surface of fresh stumps. Once the stump has become infected, the fungal hyphae seek to colonize the stump roots. The disease spreads to other trees through the contact between the roots of the infected stump and the healthy roots of nearby trees. After a site has been infected for a few years, this method of transmission gives rise to a more or less circular mosaic of dead trees. The French common name of the disease, "maladie du rond", comes from this circular pattern of areas of mortality.

Trees younger than 15 years that have a major portion of their root system killed by Heterobasidion irregulare exhibit crown symptoms typical of other root diseases (i.e., reduction in leader and branch growth, chlorotic foliage, and a distress cone crop). In more mature trees, however, the fungus causes a butt rot and external symptoms are not readily discernible. Trees with extensive decay in the structural roots are subject to windthrow, and groups of windthrown trees may indicate the presence of pockets of annosus root rot.

The fungal fruiting bodies are present at the base of the stumps and at the base of dead or dying trees. They are white on the underside and contain many pores, and the top is brown. The spores produced by these fruiting bodies become dispersed and induce new infections.

Other information

This disease possibly migrated from Mexico to the northern regions of North America.

Although this disease is uncommon in eastern Canada, except in Ontario, it represents a real threat for pine plantations. Since the disease spreads mainly in the fall, it is best to fell trees in the spring in order to limit its spread. On the West Coast, spores are present in the air throughout the year and can be carried by air currents for many kilometres. Infection by spores occurs through wounds on stems or roots, or through cut surfaces of fresh stumps. The fungus moves to surrounding trees through root grafts or root contact. Stand thinning treatments or damage to trees from logging operations can therefore exacerbate annosus root rot problems. H. irregulare is able to survive in stumps for several decades.

There are few registered products for treating stumps following cutting. For information on the products registered for controlling specific insects or diseases, please contact the Pest Management Information Service of the Pest Management Regulatory Agency (PMRA), at the following toll-free number: 1-800-267-6315.

Other control recommendations include shortened rotations and avoidance of wounding during logging. Immature fruiting bodies of this fungus could be confused with Fomitopsis pinicola but can generally be distinguished by the location on the tree. In addition, F. pinicola has very regular pores (pin-hole like) whereas the pores of H. irregulare are irregular in shape.

References

Laflamme, G.; Blais, R. 1995. Détection du Heterobasidion annosum au Québec. Phytoprotection 76:39-43.

Laflamme, G. 2011. Spread of Heterobasidion irregulare in eastern Canada towards northern natural forests of Pinus banksiana. Proceedings, IUFRO root and butt rot, Florence, Italie (in press)

Linzer, R. E.; Otrosina, W. J.; Gonthier, P.; Bruhn, J.; Laflamme, G.; Bussières, G.; Garbelotto, M. 2008. Molecular Phylogenetics and Evolution 46:844-862.

Myren, D.T.; Laflamme, G.; Singh, P.; Magasi, L.P.; Lachance, D. 1994. Maladies des arbres de l’est du Canada. Ressour. nat. Can., Serv. can. for., Administration centrale, Dir. générale des sciences et du développement durable, Ottawa (Ontario). 159 pp.

Otrosina, W. J.; Chase, T. E.; Cobb Jr, F. W.; Korhonen, K. 1993. Population structure of Heterobasidion annosum from North America and Europe. Can. J. Bot. 71:1064–1071.

Otrosina, W. J.; Garbelotto, M. 2010. Heterobasidion occidentale sp. nov. and Heterobasidion irregulare nom. nov.: a disposition of North American Heterobasidion biological species. Fungal Biology 114:16-25.

Otrosina, W.J.; Scharpf, R.F. (tech. coord.), 1989. Proc. Symp. on research and management of annosus root disease (Heterobasidion annosum) in western North America. USDA For. Serv., Gen. Tech. Rep. PSW 116.