Spruce Bud Blights

Camarosporium strobilinum E. Bommer, M. Rousseau & Sacc. 
Dichomera gemmicola A. Funk & B. Sutton 
Gemmamyces piceae (Borthw.) Casagrande 

Host(s) in Alaska:

black spruce (Piceae mariana)
Colorado blue spruce (P. pungens); ornamental
Lutz spruce (P. glauca x sitchensis)
Sitka spruce (P. sitchensis)
white spruce (P. glauca)

Habitat(s): Buds, twigs

Current Status & Distribution in Alaska (2023 Update)

Spruce bud blight is found throughout the state (see Detection Map). Three fungal species cause nearly identical bud blight disease of spruce that can only be distinguished based on spore appearance under a compound microscope. Bud blight was detected at 49 locations in 2023. The single spruce bud blight detection in Southeast Alaska was identified as Dichomera gemmicola on Sitka spruce in Juneau. Two samples of Gemmamyces piceae were identified on white spruce in Anchorage. The 46 locations with unidentified spruce bud blight were in Interior and Southcentral Alaska, with disease on Lutz spruce at two locations on the Kenai Peninsula and on white spruce at all other locations.

Overall, there have been more than 450 total observations of blighted spruce buds in Alaska on white, Sitka, and Lutz spruce (Sitka-white spruce hybrid) in the forest, and Colorado blue spruce in ornamental settings. There has been no observed mortality from the disease. Most affected trees have trace infection (1-5%), although some trees have up to 100% of buds infected. We have confirmed Gemmamyces piceae at 155 sites from near Anchor Point to north of Fairbanks. Fairbanks appears to be a hotspot for this fungus, but that may be an artifact of sampling effort. Dichomera gemmicola has been documented at 58 locations and Camarosporium strobilinum at 23 locations.

Gemmamyces piceae occurs in several locations in Europe and has caused widespread mortality of plantation blue spruce in the Czech Republic. Here, it has been documented throughout mainland Alaska, from the Kenai Peninsula to north of Fairbanks. Gemmamyces piceae has not been found in Southeast Alaska or along Prince William Sound; therefore, we will continue to collect and identify all spruce bud blight observed in coastal Alaska for species determination. Dichomera gemmicola has the widest distribution. It has been recorded on white and Lutz spruce from near Lake Clark on the Alaska Peninsula, Talkeetna, and Chicken; it has not been found near Fairbanks. Dichomerra gemmicola is the most common bud blight on Sitka spruce in Southeast, but can be difficult to detect without dedicated surveys due to its very low damage severity and subtle symptoms. Camarosporium is more prevalent on white spruce in Southcentral up to the Alaska Range, with single points near Fairbanks and on a Sitka spruce in Southeast, respectively.

In 2021, Sergio Peralta, a graduate student from University of Nebraska-Lincoln, collected 133 samples from Interior and Southcentral Alaska ranging from the Chatanika River north of Fairbanks to Homer. According to microscopic results, D. gemmicola was much more prevalent in Southcentral and Southeast Alaska. In contrast, G. piceae was common from the Kenai Peninsula to Fairbanks and can co-occur with either C. strobilinum or D. gemmicola. Whole genome squencing and phylogenetic analyses of DNA barcoding genes in 2022 indicate that all three species are closely related as they share a most recent common ancestor within the Melanommataceae family in the order Pleosporales. Not only are these three species closely related, but they can be found in the same locations, trees, or even buds. Interestingly, this close relationship suggests this group of fungi may have originated by sympatric speciation (taking place without geographic separation) despite violating an important principle of ecological theory. To further understand the status of G. piceae in Alaska, a population genetic analysis of 115 G. piceae individuals from 23 unique sites was conducted. Although most of the alleles at ten Simple Sequence Repeats (SSR) loci were invariant, an exception was observed at Anchorage’s Far North Bicentennial Park (the first location this fungus was found in Alaska) wherein seven haplotypes were detected among nine individuals. This represents relatively high genotypic diversity, which may indicate long-term sexual reproduction or multiple introductions to this location. More loci will be evaluated to fully elucidate the origin of G. piceae by the development of a genome-wide approach (AmpSeq) to genotype 96 individual isolates.

Historic Activity

Blighted spruce buds (entirely or partially dead from a fungal infection) were first noted in Alaska on ornamental Colorado blue spruce near Homer in 2013. In 2014 it was found for the first time on native white spruce in the forest near Anchorage. Identification of Gemmamyces piceae by Forest Health Protection in Alaska became possible with a 2016 publication reporting a sudden spruce bud blight outbreak in Colorado blue spruce plantations in the Czech Republic (Cerny et al. 2016). The publication describes a massive outbreak that was first detected in 2009 and has now been found across the Czech Republic. Bud loss quickly reached 80-100% in highly infected trees and stands. The fungus has been reported since 1906 from Austria, Czech Republic, Denmark, Finland, Russia, Scotland, and Switzerland (Borthwick 1909). In these locations, it has primarily been found in human-altered situations (e.g., urban ornamentals, nurseries and forest plantations) on the North American tree hosts Colorado blue spruce and Engelmann spruce, but Sitka spruce and white spruce were also susceptible to a lesser degree. Neither the fungus, nor the disease it causes, were found within the native range of Norway spruce in Europe until 1946. It has been speculated that the fungus is native to Asian spruce from the Tianshan Mountains in China (Cerny et al. 2016). However, a recent paper made an apparently unsupported claim that it is widespread in North America (Jaklitsch & Voglmayr 2017). Only two prior North American records have been located, both from 1990 in New Brunswick and Nova Scotia on the east coast of Canada. Dichomera bud blight was first described in the early 1960s from British Columbia, where it has been more frequently reported on inland Douglas-fir, Engelmann spruce and white spruce than on coastal Sitka spruce (Funk and Sutton 1973). This disease usually is not a significant concern.  

Symptoms, Biology & Impacts

These diseases are recognized by black, swollen, misshapen buds and deranged growth patterns. The causal fungus infects through the bud and may kill buds prior to bud break. Infected shoots that are not killed characteristically grow around developing lesions, resulting in twisted, zigzagged branches and axillary bud proliferation. The symptomatic branch can be used to date the original infection (based on the affected branch cohort). After several years of bud loss, trees may wither and die.

Our observations to date suggest that Camarosporium sp. is a weak pathogen. The fruiting structures tend to be produced less densely, primarily towards bud tips. Affected stems seldom exhibit zigzag growth patterns.

Survey Method & Frequency

FHP installed monitoring plots near Anchorage and Fairbanks in 2016 and found that damaged buds affected up to 40% of the trees within 50ft-radius plots. Most affected trees have very few damaged buds (less than 5%), but highly infected trees can have up to 100% of the buds dead or damaged.

In 2017, we installed monitoring plots (182 plots) and conducted informal surveys to gather presence/absence information and disease severity information statewide. Three different sampling designs (fixed-radius plots, timed meanders and transects) were employed depending upon location, access, and available resources. In conjunction with this intensive sampling effort, Dr. Gerard Adams (University of Nebraska Lincoln) determined that identical signs and symptoms were caused by three different fungal pathogens. Despite an effort to collect sexual fruiting structures of G. piceae in Alaska in 2017 and 2018 for a population genetics study, this fungal pathogen has proven extremely difficult to obtain in pure cultures. This work was intended to provide insight as to how long the fungus has been present in Alaska based on genetic diversity. Higher diversity would support a relatively longer time-since-establishment and likely native status. Its widespread occurrence, generally low levels of damage, and infections dating back a decade or more at many sites suggest it is native or long-established, while the lack of reports in Alaska prior to 2013 and limited detection in North America may point to a more recent introduction. 

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Detection Map

Links to Resources & Publications

¹ Černý, K., Pešková, V., Soukup, F., Havrdová, L., Strnadová, V., Zahradník, D., & Hrabetová, M. 2016. Gemmamyces bud blight of Picea pungens: A sudden disease outbreak in central Europe. Plant Pathology, 65(8): 1267-1278. Available here.

² Borthwick A.W. 1909. A new disease of Picea. Notes from the Royal Botanic Garden, Edinburgh, 4: 259–61.

³ Jaklitsch W.M. & Voglmayr H. 2017. Three former taxa of Cucurbitaria and considerations on Petrakia in the Melanommataceae. Sydowia 69: 81–95.

⁴ Funk, A. and B. C. Sutton. 1973. A disease of conifer buds in western Canada associated with Dichomera gemmicola n. sp. Canadian Journal of Botany 50(7): 1513-1518. Available here.

Forest Health Conditions in Alaska - 2016

Global Diversity Information Facility - Gemmamyces piceae

USDA National Fungus Collection Database - Gemmamyces piceae

Natural Resources Canada- Pacific Forestry Centre's Forest Pathology Herbarium DAVFP Collections Database - Dichomera gemmicola

Content prepared by: Lori Winton, PhD Southcentral and Interior Alaska Forest Pathologist, Forest Health Protection, loretta.winton@usda.gov and Robin Mulvey, Southeast Alaska Forest Pathologist, robin.mulvey@usda.gov.
 

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