Junghuhnia vincta var. vincta - a root rot pathogen of Hevea in Mexico
by: E. Setliff
J. vincta var. vincta (Berk.) I.A. Hood & M.A. Dick var. vincta is a tropical to subtropical root rot pathogen that occurs in North America as far north as about 31° N latitude (Saucier, MS) along the Gulf Coast of the U.S. (1). In the field, var. vincta basidiocarps vary in pore surface coloration from ochraceous (Fig. 1) to pinkish-orange-gray (Fig. 2) and are similar in outward appearance to other Junghuhnia species. Also, there is macroscopic similarity with Rigidoporus albostygius (Berk. & M.A. Curtis) Rajchenb. except that the latter is much more pinkish when fresh [See forthcoming MycoNote 5]. Microscopically, J. vincta is recognized by having subglobose basidiospores (Fig. 3), obovate to cylindrical incrusted skeletocystidia (Fig. 4) and gloeopleurous mammiform cystidia (1,2) each with a papillum (Fig. 5).
J. vincta is present but unreported in the U.S. as a pathogen, however Weir (3) observed J. vincta on rubber (Hevea braziliensis) in Amazonia (Para, Brazil). Also, WJ Martin collections from Mexico in the SYRF herbarium labeled “A” and “B” showed fruiting bodies of J. vincta associated with decayed roots of rubber seedlings. In the southern U.S., vincta root rot may have been overlooked because the foliar symptoms are so similar to those caused by annosus and armillaria root diseases. Research will need to determine the level of virulence in American isolates. With the warming trend over the last several decades, the distribution of J. vincta may expand northward. Ecological exclusion also may be a controlling aspect of distribution.
In other locations, vincta root rot was reported on Aracaria cunninghamii (hoop pine) in Queensland, Australia (4), Pinus radiata in New Zealand (5) as well as other native plants (6, 7). The Australian fungus Poria hyposclera (Berk. ex Cooke) Sacc., TYPE on banana corm is synonymous with J. vincta var. vincta (2). The mammiform cystidia in the TYPE of P. hyposclera were more asymmetrical than those in North American collections. Differences in pore surface coloration has caused much confusion in the Poria vincta complex [See forthcoming MycoNotes 2, 3 and 5].
Acknowledgements: My thanks go to Drs. H.H. Burdsall and Karen Nakasone for their hospitality and laboratory support during my enjoyable visits to the Center for Forest Mycology Research (CFMR), U.S. Forest Service, Northern Research Station, Madison, WI. Photomicrographs shown in Figs. 3-5 were taken at CFMR.
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Created 5 June 2012