Anisogramma anomala (eastern filbert blight)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Sordariomycetes
Subclass	Sordariomycetidae
Order	Diaporthales
Family	Valsaceae
Genus	Anisogramma

Scientific Name

Anisogramma anomala

Common Name

Eastern filbert blight

Author:Elizabeth Bush, Virginia Tech

Reviewed by:Jay W. Pscheidt, Oregon State University

Pathogen

Anisogramma anomala is an extremely damaging pathogen on European hazelnut (Corylus avellana), also known as filbert, causing perennial cankers that girdle branches and eventually result in tree death if not managed.

Symptoms and Signs

The elliptical stromata (1.5-3.0 x 2-10 mm and 1-2 mm tall) of A. anomala are arranged along the length of branch cankers and are diagnostic for the disease. The stromatal surface is initially white and later darkens as perithecia develop. On 1-year-old cankers 1 to 2 rows of stromata typically develop, but in older cankers additional rows are produced. Stromata contain 50 to 100 immersed perithecia. The mature, dark-walled perithecium is ovate to pear-shaped and measures 250 to 830 x 1,040-2,160 µM. The asci are broadly clavate and unitunicate, measure 10-15 x 45-65 µM, have a thin, thread-like stipe and contain 8 spores. Ascospores are hyaline and have two unequally-sized cells: A small, degenerate, cap-like cell (1.1 to 1.4 x 1.1 µM) and a large, biguttulate cell that measures 8-12 x 4-5 µM when mature. After ascospores are discharged stromata are still visible, but deteriorate over time.

Ecology and Spread

A. anomala is an indigenous and non-consequential pathogen on American hazelnut (Corylus americana), which is an understory tree in northeastern North America. The ecology and lifecycle of this pathogen has been studied extensively in the Pacific northwest of the U.S. where European hazelnut (filbert) production is an important agricultural industry. Therefore, the following description of the ecology and lifecycle of this pathogen relates to research done in the Pacific Northwest. The only spore type known is the infective ascospore. Ascospores are forcibly released during and after rainfall. In western Oregon the majority of ascospores are released in the winter and early spring when trees are not susceptible to infection; however, they continue to be released through mid- to late- spring (May) during which time trees begin to produce new, susceptible shoots. Springtime is the critical infection period. During rain events ascospores are released in large quantities. New infections occur through dispersal of ascospores by jboth rain splash and wind. Movement of ascospores has been shown to be primarily downwind. Natural geographic movement of the disease is slow; however, the disease can also be moved to new locations by means of infected nursery stock/plant material.

On new shoots only immature tissue near the apical bud is highly susceptible to infection by ascospores of A. anomala. Therefore, trees are only highly susceptible to infection during the period of new growth in spring: Specifically from mid-to late March when new leaves emerge and in April when new shoots elongate. Temperatures from 8 to 25C that occur during periods of high humidity from 24- to 72-hours favor infection. After infection the fungus penetrates into the phloem, cambium and outer xylem layer. Stromata develop in cankers only after the tree has been dormant, in approximately a year to 14 months after infection. Cankers elongate both lengthwise along branches and by production of additional rows of stromata annually. The pathogen does not survive saprophytically on dead branch tissue and no resting structure has been identified; therefore, A. anomala appears to be an obligate, biotrophic pathogen on filbert.

Geographic Distribution

When the European hazelnut (C. avellana) was introduced to North America and cultivation was attempted in the early part of the 20th century, eastern filbert blight was identified and found to be so destructive that cultivation of European filbert was abandoned. Quarantines were instituted to prevent spread to the Pacific Northwest and other locations where European hazelnut was cultivated and the disease was not present. A. anomala has been reported in the following locations east of the Rocky Mountains in the U.S.: Connecticut, Delaware, Illinois, Iowa, Maine, Maryland, Massachusetts, New Jersey, New York, and North Carolina. In 1973 the pathogen was identified on European hazelnut in an orchard in southwestern Washington; from there it spread to other orchards and became endemic. By 1986 the disease had spread to northeastern Oregon and by the mid-1990s it was widespread in many of Oregons’s hazelnut orchards. A. anomala has also been reported in Canada (British Columbia, Manitoba, Nova Scotia, Ontario and Quebec). A. anomala is currently on the quarantine list for the European and Mediterranean Plant Protection Organization (EPPO).

Management

Management recommendations for eastern filbert blight are designed to 1) detect the disease before it has established in an orchard or landscape and 2) manage or slow the progress of the disease where is has already become established. Management of eastern filbert blight requires an integrated management approach that includes diligent scouting, fungicide applications, pruning, and sanitation. However, once the disease is present on a susceptible cultivar of European hazelnut, acceptable levels of control are unlikely. However, on moderately susceptible cultivars, the progress of the disease may be slowed significantly. Minimizing the number of cankers, which are perennial and expand up to 1 meter in length on susceptible cultivars annually, in an orchard situation is critical to successful management. In Oregon, which represents 98% of European filbert acreage and where most research on the disease has occurred, the recommendation is to scout orchards at least twice annually. When trees are in foliage, look for flagging leaves to locate areas to check for potential cankers; in the winter look for cankers on branches. Small cankers on shoots (previous year’s new growth) near tree tops are difficult to see and this is typically where the first cankers on a tree develop. Unfortunately, the disease has been present 3 to 5 years when cankers are typically noticed by growers.

Since new plant material could harbor the pathogen (i.e. have a latent infection), it is especially important to scout new stock regularly after planting and remove any diseased trees to avoid spread in an orchard or landscape. Trees are susceptible to infection beginning at budbreak and during leaf emergence and initial shoot elongation. Protectant fungicides, such as chlorothalonil and copper hydroxide products, used during the infection period have provided protection to European hazelnut when sprays are initiated in the spring at budbreak and repeated at intervals of 8- to 17- days. Systemic fungicides may be more effective than protectant products when shoots are rapidly elongating.

Overwintering of the fungus occurs on cankered branches, so cankered branches should be pruned-out during the winter. Prune up to 0.6 to 0.9 meters below cankers on susceptible cultivars (early infection and colonization of the fungus in branches does not produce visible symptoms). Remove cankered branches from the orchard or landscape or burn or chip. In severe cases removal of all branches other than main scaffold limbs has been practiced. Growers must protect new growth that emerges after pruning since new growth is very susceptible to the disease. Other sanitation practices that can reduce inoculum available for new infections include replacing susceptible pollinizer hazelnuts with more resistant pollinizer cultivars and rouging out any volunteer hazelnuts and native filberts that may harbor the fungus.

European hazelnut cultivars possess a range of susceptibility to eastern filbert blight. Resistant ornamental and nut-producing cultivars with horticulturally acceptable traits are available. Unfortunately, cultivars resistant to strains of the pathogen in Oregon (used in breeding programs) may not be resistant to strains of A. anomala present in the eastern U.S. Oregon State University has had a robust filbert breeding program and cultivars have been bred that have quantitative resistance or single gene resistance. For new plantings select resistant cultivars and also resistant pollinizer cultivars when possible. An ornamental cultivar, ‘Red Dragon’, of C. avellana with contorted growth is available in the nursery trade and may be a good replacement in some locations for the eastern filbert blight susceptible C. avellana var. contorta, also known as Harry Lauder’s Walking Stick, which is a popular ornamental hazelnut.

Diagnostic procedures

Early detection of A. anomala in branch tissue prior to development of cankers has traditionally been very difficult since A. anomala is an obligate pathogen and biotrophic. Specialized media and skills/techniques are required that make culturing this fungus in a general diagnostic laboratory impractical. Since there is a long latent phase before symptoms appear early detection has been problematic for breeding programs and for management of the disease. ELISA has been used by researchers to detect early (i.e. asymptomatic) infections of the fungus, but commercial kits are not available. Recently real-time PCR primers and a Taqman® probe have been developed that are highly specific and sensitively detect A. anomala in early stages of infection (i.e. asymptomatic) in branch tissue. Using this primer/probe set Molnar et al. (2013) detected the pathogen directly from DNA extracted from branch tissue. Six weeks post-inoculation the test detected the pathogen in 79% of infected branches; at 15 weeks and 29 weeks post-inoculation the pathogen was detected in 90% and 100% of infected branches, respectively. The first visible symptoms of the disease occur before canker development: The phloem and cambial tissues become discolored chocolate-brown. Check for this symptom in the spring by peeling bark back from suspect branches. Later in disease development (typically from 12-16 months post-infection in the Pacific northwest) the disease is easily recognized by the perennial branch cankers that begin to develop and contain a row or rows of closely spaced elliptical stromata, described above.

Resources and References

1. Anonymous. 2013. Anisogramma anomala. in: EPPO A1 List of pests recommended for regulation as quarantine pests.

2. Anonymous. 2014. Anisogramma anomala. in: PQR-EPPO Plant Quarantine Data Retrieval System.

3. Pscheidt, J. W.. Eastern Filbert Blight Help Page. Oregon State University Extension Service. Online: http://oregonstate.edu/dept/botany/epp/EFB/ .

4. Barss, H. P. 1921. Eastern Filbert Blight Problem. Pages 251-253 in: The Monthly Bulletin: California State Department of Agriculture.

5. Gottwald, T. R., and Cameron, H. R. 1980. Infection site, infection period, and latent period of canker caused by Anisogramma anomala in European filbert. Phytopathology 70:1083-1087.

6. Gottwald, T. R., and Cameron, H. R. 1979. Studies in the morphology and life history of Anisogramma anomala. Mycologia 71:1107-1126.

7. Heckert, S., Pscheidt, J. W., and Cluskey, S. A. 2014. Disease Incidence and Ascospore Dispersal from Cut Hazelnut Branches Colonized by Anisogramma anomala. Plant Disease 98:834-838.

8. Johnson, K. B., Mehlenbacher, S. A., Stone, J. K., Pscheidt, J. W., and Pinkerton, J. N. 1996. Eastern filbert blight of European hazelnut. It's becoming a manageable disease. Plant Disease 80:1308-1316.

9. Mehlenbacher, S. A. 2002. Eastern filbert blight. Pages 44-46 in: Compendium of nut crop diseases in temperate zones. B. L. Teviotdale, T.J. Michailides, and J.W. Pscheidt, eds. American Phytopathological Society Press, St. Paul, MN.

10. Mehlenbacher, S. A., and Smith, D. C. 2009. 'Red Dragon' ornamental hazelnut. HortScience 44:843-844.

11. Mehlenbacher, S. A., Smith, D. C., and McCluskey, R. L. 2013. 'Dorris' hazelnut. HortScience 48:796-799.

12. Mehlenbacher, S. A., Smith, D. C., and McCluskey, R. L. 2011. 'Jefferson' hazelnut. HortScience 46:662-664.

13. Mehlenbacher, S. A., Smith, D. C., and McCluskey, R. L. 2014. 'Wepster' hazelnut. HortScience 49:346-349.

14. Mehlenbacher, S. A., and Thompson, M. M. 1991. Four hazelnut pollenizers resistant to Eastern filbert blight. HortScience 26:442-443.

15. Molnar, T. J., Walsh, E., Capik, J. M., Sathuvalli, V., Mehlenbacher, S. A., Rossman, A. Y., and Zhang, N. 2013. A real-time PCR assay for early detection of eastern filbert blight. Plant Disease 97:813-818.

16. Sinclair, W. A. and Lyon, H. H. 2005. Eastern Filbert Blight. Pages 158-159 in: Diseases of Trees and Shrubs. Comstock Publishing Associates, Cornell University Press, Ithaca, NY.

Acknowledgements

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)