Taphrina caerulescens (leaf blister on oak)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Taphrinomycotina
Class	Taphrinomycetes
Order	Taphrinales
Family	Taphrinaceae
Genus	Taphrina

Scientific Name

Taphrina caerulescens

Common Name

oak leaf blister

Author: Clarissa Balbalian, Mississippi State University

Reviewed by: Matthew T. Kasson, Virginia Tech

Pathogen

Taphrina caerulescens is a filamentous ascomycete and obligate parasite of oak (Quercus spp.). On the leaves of the oak host, the fungus forms unprotected "naked" asci that are characteristic of Taphrina sp. Asci are cylindric or clavate, rounded at the top, 30-120 μm x 11-34 μm. Each ascus contains 8 nearly globose ascospores about 5.5 μm in diameter, however ascospores are rarely observed. Instead, asci are typically filled with yeast-like conidia formed inside the ascus by enteroblastic budding directly off the ascospore. Blastospores are ovate to elliptic and 3-7 μm x 1-1.5 μm.

In culture the fungus is yeast-like and composed of unipolar, budding blastospores. Colonies on potato dextrose agar are opaque and pale pink. The pink color darkens with age. Colonies are circular with entire margins, smooth, viscid, and glisten. Ascospores are not formed in culture.

Symptoms and Signs

Leaf spots start out as pale green to yellow and are slightly swollen, convex-concave blisters that vary in size. As the leaf matures, the spots become necrotic. A layer of asci form on the lower leaf surface (concave side). When fresh, the layer of asci resembles a palisade-like layer that is translucent-white and granular on the leaf surface. The fungus also can deform the entire leaf.

Ecology and Spread

Taphrina caerulescens infects the genus Quercus (oak). The fungus overwinters as blastospores on twigs and in bark scales. In the spring these spores can infect leaves as they emerge from buds. Infection is indirect and occurs through leaf stomates. Blastospores that bud off of ascospores are forcibly discharged from infected leaves and can reinfect the host or grow saprophytically on the leaf surface in a yeast-like phase. Severity of the disease is dependent on environmental conditions. Wet springs enhance disease severity.

Geographic Distribution

Taphrina caerulescens is endemic to North America, occurring throughout the United States and Canada. The fungus has also been reported from Asia, Africa and Europe.

Africa: Algeria and Morocco Asia: Armenia, China, Japan, and Korea Europe: Austria, Denmark, France, Germany, Greece, Ireland, Italy, Norway, Portugal, Sicily, Spain, Ukraine, United Kingdom, USSR, and Yugoslavia

Management

Management of any pathogen is often dependent upon both cultural and chemical options. Consult your local extension specialist or agent for recommendations relevant to your particular host and state. Chemical management of oak leaf blister is rarely recommended because injury to the tree is primarily aesthetic. To be effective, fungicides must be applied preventively in the spring, at bud break. Products containing the active ingredient chlorothalonil are labeled for use on the red oak group only. The active ingredient mancozeb is labeled for use on oak in general.

Remember: the label is the law.

Diagnostic procedures

Leaf blisters on an oak host, and the presence of naked asci characteristic of Taphrina sp. are good diagnostic characteristics for field and microscopic diagnosis. The fungus can be isolated on potato dextrose agar or acidified PDA, and produces similar cultural characteristics on malt agar, or pea agar as well. A useful technique for isolating the fungus is to fasten a piece of the leaf tissue to the lid of the petri dish, with the ascospore-bearing surface facing the agar surface. Incubate cultures at 20-25°C. Taphrina sp. also produce a negative diazonium blue B (DBB) reaction, negative extracellular DNase activity and postive urease activity.

Resources and References

• Camp, R.R., and W.F. Whittingham. 1974. Ultrastructural alterations in oak leaves parasitized by Taphrina caerulescens. American Journal of Botany, 61(9): 964-972.
• Martin, E.M. 1925. Cultural and morphological studies of some species of Taphrina. Phytopathology, 15: 67-76.
• Mix, A.J. 1949. A monograph of the genus Taphrina. University of Kansas Bulletin, 33(1): 3-167.
• Nagao, H. and K. Katumoto. 1998. Leaf blister of Quercus phyllyraeoides caused by Taphrina caerulescens. Mycoscience, 39: 173-178.
• Sinclair, W.A. and H.H. Lyons. 2005. Diseases of Trees and Shrubs, second edition. Cornell University Press. Ithaca, NY.
• Taylor, J. and D.O. Birdwell. 2000. A scanning electron microscopic study of the infection of water oak (Quercus nigra) by Taphrina caerulescens. Mycologia, 92(2): 309-311.
• USDA-ARS Systematic Mycology and Microbiology Fungal Database. http://nt.ars-grin.gov/fungaldatabases/index.cfm

Acknowledgments

• 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)