Botryosphaeria canker of spruce
- French disease name: Chancre botryosphaérien
- Pathogen name: Botryosphaeria piceae Funk
- Kingdom: Fungi
- Phylum: Ascomycota
- Class: Dothideomycetes
- Order: Botryosphaeriales
- Family: Botryosphaeriaceae
General information and importance
The fungus Botryosphaeria piceae causes Botryosphaeria canker of spruce trees in British Columbia. This native species infects young to mature spruce trees in natural forest stands. The fungus is thought to enter through wounds or weakened areas on the tree, although the exact infection process remains unclear. The disease is generally not considered serious because infected branches often survive for many years, even with extensive infections. Disease outbreaks tend to be more severe in young trees growing in poor site conditions. Botryosphaeria piceae seems to spread slowly in natural forest ecosystems. Further studies are needed to determine if environmental factors, such as climate change, might influence its severity or spread in future outbreaks. Additional research is needed to better understand its impact on tree health and infection pathways.
Distribution and hosts
Botryosphaeria piceae infects Engelmann spruce (Picea engelmannii), white spruce (P. glauca), and Sitka spruce (P. sitchensis) within their respective ranges in central, eastern, northern, and coastal British Columbia.
Tree parts affected
Branches and stems are affected by perennial cankers.
Symptoms and signs
Infection by B. piceae causes large, corky, canker-like swellings on susceptible spruce species. Botryosphaeria canker of spruce typically begins on branches but can spread to the main stem in severe cases, potentially compromising tree structure. Perennial lesions develop on living stems and branches, which may become completely covered with sexual reproductive structures (ascostromata). Ascostromata are black, globose, and densely gregarious, sometimes occurring on a common basal stroma. They measure 0.4 to 0.8 millimetres in diameter and up to 1 millimetre high and are uniloculate. The asci borne within the ascostromata are clavate, short-stalked, bitunicate, and eight-spored, usually measuring 240 to 280 micrometres × 67 to 84 micrometres, and are surrounded by hyaline pseudoparaphysoids. Ascospores are hyaline at first and become black upon germination. They are ellipsoid, aseptate, and range in size from 60 to 85 micrometres × 26 to 42 micrometres
Disease cycle
Botryosphaeria piceae ascospores are released from cankers on Sitka spruce between February and April, whereas on Engelmann spruce, release occurs from early spring through summer, though to a lesser extent. The differences in spore-release timing may be due to climatic differences between the two host ranges. Although the infection pathway remains poorly understood, it is likely similar to other Botryosphaeria species, with ascospores entering through wounds or via endophytic infections of the needles. Ascostromata arise from an intraperidermal layer of dark stromatic tissue on the living branches and are erumpent through the periderm in large, densely aggregated clusters across a large area of the branch surface. Old ascostromata persist in the centre of the perennial canker, whereas new ascostromata develop near the advancing margin.
Damage
Mature trees typically show resilience to the disease, but saplings and young trees growing in nutrient-poor conditions may experience higher mortality rates. Botryosphaeria cankers are perennial and often encircle branches completely, potentially disrupting water and nutrient flow. Death of branches may occur directly due to the girdling effect of the cankers, or indirectly due to secondary infections or environmental stress. Extensively infected branches can often remain alive for several years. Despite high infection rates, forest stands heavily infected by B. piceae do not appear to have significant adverse effects. Infected branches may lead to localized deformities in tree form due to the presence of large cankers, though growth loss appears minimal in most cases. Trees affected by Botryosphaeria cankers may become more susceptible to other pests or environmental stressors, such as windthrow, due to weakened branch structure.
Prevention and management
Treatment of forests for Botryosphaeria canker of spruce is not necessary in British Columbia due to the resilience of mature trees and the generally low levels of damage associated with this disease. Young spruce are more susceptible to this pathogen. Avoid planting spruce on poor sites.
Pest management strategies for a particular pest vary depending on several factors. These include:
- the population level of the pest (i.e., how numerous the pest is on the affected host[s]);
- the expected damage or other negative consequences of the pest’s activity and population level (either to the host, property, or the environment);
- an understanding of the pest’s life cycle, its various life stages, and the various natural or abiotic agents that affect population levels;
- how many individual host specimens are affected (an individual tree, small groups of trees, plantations, forests);
- the value of the host(s) versus the costs of pest management approaches; and
- consideration of the various silvicultural, mechanical, chemical, biological, and natural control approaches available and their various advantages and disadvantages.
Decisions about pest management strategies require information about each of these factors for informed decision-making. These various factors should then be weighed carefully in terms of costs and benefits before action is taken against any particular pest.
Selected references
Crous, P.W.; Slippers, B.; Wingfield, M.J.; Rheeder, J.; Marasas, W.F.O.; Philips, A.J.L.; Alves, A.; Burgess, T.; Barber, P.; Groenewald, J.Z. 2006. Phylogenetic lineages in the Botryosphaeriaceae. Studies in Mycology 55: 235–253. https://doi.org/10.3114/sim.55.1.235
Funk, A. 1965. A new parasite of spruce from British Columbia. Canadian Journal of Botany 43(1): 45–48. https://doi.org/10.1139/b65-006
Funk, A. 1978. Canker disease of spruce. Fisheries and Environment Canada, Canadian Forestry Service, Pacific Forest Research Centre. Victoria, British Columbia. Forest Pest Leaflet No. 65. 4 p.
Funk, A. 1985. Parasitic microfungi of western trees. Environment Canada, Canadian Forestry Service, Pacific Forest Research Centre. Victoria, British Columbia. BC-X-222. 190 p. https://ostrnrcan-dostrncan.canada.ca/entities/publication/5f8ee67d-67da-4617-b2e5-97bfed0acc5f?fromSearchPage=true
Rathnayaka, A.R.; Chethana, K.W.T.; Phillips, A.J.L.; Liu, J.-K.; Samarakoon, M.C.; JonesE.B.G.; Karunarathna, S.C.; Zhao, C.-L. 2023. Re-evaluating Botryosphaeriales: ancestral state reconstructions of selected characters and evolution of nutritional modes. Journal of Fungi 9(2): 184. https://doi.org/10.3390/jof9020184