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Cryptodiaporthe Canker of Pagoda Dogwood in North Dakota

Cryptodiaporthe canker, caused by Cryptodiaporthe corni (Wehm.) Petrak (anamorph Myxosporium nitidum Berk. & Curt.), is known to occur only on pagoda dogwood (Cornus alternifolia L. fil.) throughout its native range in eastern Canada and most of the eastern United States (1). Cankered branches with yellow-to-orange pigmented bark were recently observed on four ≈25-year-old C. alternifolia plants in an ornamental planting on the campus of North Dakota State University in Fargo. Although the fungal anamorph was usually present on all symptomatic materials, the teleomorph was also present on branches with larger diameters (>15 mm). Collections of infected branches made on 25 April 2001 contained perithecia but did not contain mature ascospores. Shoot growth began during the first week of May. Subsequent collections made on 11 May and 8 June 2001 contained perithecia with mature ascospores. A previous collection made on 12 October 2000 contained fully developed perithecia devoid of ascospores. A range of symptoms was present among the individual trees: one tree was severely cankered (up to 4 cm diameter) with many dead branches; one tree showed only minor damage with tip dieback on a few small twigs; and two trees had intermediate symptoms (1 cm diameter with cankers) with several dead branches. Pagoda dogwood is generally seed propagated, and differences in disease severity observed in these plants may be the result of genetic variation in resistance. Selection for resistant genotypes may be a possibility. Specimens (BPI 840955A and B) consisting of cankered branches containing both fungal morphs were deposited at the U.S. National Fungus Collections at Beltsville, MD. Although Cryptodiaporthe canker was previously collected from a native woodland tree in Minnesota (1), the current North Dakota specimens were collected from cultivated plants in a landscape setting. To our knowledge, this is the first report of Cryptodiaporthe canker in North Dakota. Management of this disease may need to be considered when recommending C. alternifolia for horticultural plantings.

Reference: (1) S. C. Redlin and A. Y. Rossman. Mycologia 83:200, 1991.