A CENANGIUM ASSOCIATED WITH SOOTY-BARK CANKER OF ASPEN 1

Ross W_ Davidson and Edith K. Cash 2

Sooty-hark canker of aspen, descrihed here forthe first time, is reported from the central RockyMountains. It is common mainly in mature andover-mature stands and occurs at various heightson the trunk. The hark hecornes blackened andremains intact over the cankered area. ln 3 to

SUMMARY

5 years, a discomycete fungus, Cenangium singulare(Rehm) comb. n. fruits abundantly on the cankeredbark. The fungus may occur in the centers ofcankers hefore they girdle the affected trees, butit is most abundant on diseased bark of killed trees.

Aspen (Populus tremuloides Michx.) is subject to anumher of canker diseases. Meinecke (3), in hisstudy of diseases of aspen in Utah, mentioned acommon trunk canker that is characterized by con-centric areas of exposed wood surrounded at thecanker margins by flaring, outrolled, dead bark.In Colorado, this canker occurs on occasional treesscattered through young or old stands. It is alsoabundant in localized areas where almost every tree isinfected. Often an affected tree may have a large, oldcanker near the base of the trunk and other pro-gressively smaller cankers higher up. The writershave never observed a fungus associated with thistype of canker, which Boyce (1) has referred to as"hlack canker of aspen."

Another large previously undescribed canker onaspen is common in most areas of the central RockyMountains. It is especially abundant in stands on thewestern slope of the Continental Divide in Colorado. Ithas heen tentatively named sooty-black canker ofaspen, and this paper presents a preliminary reportof the canker and describes a fungus that seems to beconsistently associated with it.

Sooty-bark canker is rather uniformly distributedthrough older or mature stands. It becomes especiallyabundant in timber that is dying from old age orother causes. The canker has seldom been found inyoung stands (up to 60 years), but is occasionallypresent in 60- to 80-year-old stands and sometimesabundant in stands 80-150 years old.

Sooty-bark canker develops rather rapidly and maygirdle a tree in a few years. Cankers develop at anypoint on the trunk up to a height of 60-70 feet. Some-

1Accepted for publication August 11, 1955.2 Forest Pathologist, Rocky Mountain Forest and Range

Experiment Station, U. S. Department of Agriculture, ForestService, with headquarters at Colorado A & M College,Fort Collins, Colorado; and Associate Mycologist, NationalFungus Collections, Horticultural Crops Research Branch,U. S. Department of Agriculture, Beltsville, Maryland,respectively,

times they start at old wounds, such as basal firescars or sun scald injuries, but they may also start atpoints where there are no apparent injuries. Cankersmay reach a length of 10-15 ft. on large stems beforethey girdle the tree. The bark over the cankered areausually remains intact and tightly attached to thewood, even after the tree dies (Fig, 1,A). Thecankers are not conspicuous but may have a slightlytarget-Iike appearance where part of the outer whitesurface has flaked away in a somewhat zoned patternexposing part of the blackened inner bark. Except forthe thin white outer layer, the bark becomes a uni-form sooty black. When the white outer surface is re-moved, the canker margin is very distinct (Fig. 1,B).

Young cankers do not fruit conspicuously, but Ire-quently numerous fruiting primordia (pycnidia?)cause roughened areas near the mar gins. None ofthese have been collected in good sporulating condi-tion. Small insects are often present and may feed onthese fruiting bodies. Cytospora chrysosperma Fr. issometimes found as a secondary fungus associated withthese cankers, but it does not cause thern.

The blackened bark usually remains tightly attachedto the wood for several years after the trees die andfaIl to the ground. The fungus seems to cement thebark to the trunk and produces a peculiar pattern onthe wood that is exposed after the hark finally weath-ers off (Fig. 1,D).

FRUITING OF CENANGIUMON OLO BARK.-Apotheciausually develop abundantly on the old diseased blackbark or underneath the loosened white surface layer(Fig. 1,C). They are light gray on the exterior andcurled up in angular to hysteroid shapes, which uponmoistening open to reveal themselves as discoid orurn-shaped (Fig. 2).

The discomycete is present at all seasons and proboably disseminates ascospores at any time of the yearwhen moisture and temperature are favorable. Thespores are forcibly ejected, indicating that they aredisseminated by wind.

FIG. 1. Sooty-bark canker of aspen. A) Canker at base of mature tree; B) Same canker with part of bark removedfrorn margin; C) Cenangium fruiting bodies on old bark; D) Wood from which old diseased bark has weathered ofI.

PHYTOPATHOLOGY for Decernber (45:639·696) was issued December 30, 1955.

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January, 1956] DAVIDSON AND CASH: ASPEN CANKER AND A CENANGIUM 35

36 PHYTOPATHOLOGY [VoI. 46

FIG. 2. Cenangium singulare (Rehm) , A) Closed apothe-cia; B) Apothecia opened or partly opened from exposureto moisture (magnified several times).

CLASSIFICATIONOF THE ASPENCANKERFUNGUS.-Thediscomycete described by Ellis and Everhart (2, p.100) in 1888 as Dermatea pruinosa Ell. & Ev., col-lected on decaying bark in Colorado by Cockerell, ap-pears to be the same as the fungus found fruiting soabundantly on the old sooty-bark cankers. Seaverplaced it in Cenangium. in 1951, making the combina-tion C. pruinosum. (EU. & Ev.) Seaver (5, p. 300).Seaver quotes from a note by Ellsworth Bethel on an1898 herbarium label that "this is abundant every-where in the mountains where aspen is found." Itsassociation with old cankered bark has not been men-tioned previously.

Apparently the species had been considered a va-riety of Cenangium. populneum by Rehm and pub-

lished as C. populneum (Pers.) Rehm var. singular eRehm by Starbãck in 1895 (6, p. 19, Fig. 7). The de-scription was copied hy Saccardo and Sydow in 1899(4, p. 796). The Ellis and Everhart name as given hySeaver (C. pruinosum) is preempted for a difIerentfungus, C. pruinosum. Ces. 1854. It is necessary, there-Iore, to rename it and the varie tal name used by Rehmis pbposed and raised to species rank as follows:Cenangiumrsingulare (Rehm) comb. n.

HERBARIUM!SPECIMENSEXAMINEO.- The 6 herhariumspecimens that foUow were examined and seemed to bethe same as. those collected recently from old cankeredaspen bark. The first 3 are from the New York Bo-tan ica l Garden; loaned through the courtesy of DI'.D. P. Rogers. The other 3 specimens are in the Na-tional Fungus Collections, Plant Industry Station,Beltsville, Maryland, and give information on distribu-tion.

Type specimen, Dermatea pruinosa Ell. & Ev., Colora do,1888, col!. T. D. A. Cockerell.

Bethel No. 258·a, on aspen, Buena Vista, Colorado, Au-gust, 1898.

Another specimen as Cenangium populneum. (changedfrom original C. [uriuraceuni) , Colorado, no other data.

Cenangium populneum. Rehm var. solare (error for sin-gulare Rehrn) . Reliquiae Farlowianae 104 on bark of Pop-ulus grandidentata, New Hampshire, May 18, 1908, W. G.Farlow.

Cenangium populneum. (Pers.) Rehm var. singulare Rehmon Populus trichocarpa, Priest Ríver, Idaho. October 1920,coll. J. R. Weir, det. E. K. Cash, Forest Path. 71044; onPopulus sp., Neebish, Mich. Oct. 1919, Herb. E. T. & S. A.Harper 1531, det. E. K. Cash.

Cenangium pruinosum. (E1l. & Ev.) Seaver, ou Populussp., S. Aurora Ontario, Oct. 2, 1932, coll. H. S. Jackson,det. F. J. Seaver.

ROCKY MOUNTAIN FOREST ANO RANGE EXPERIMENTSTATION

FOREST INSECT AND DISEASE LABORATORYFORT COLLINS, COLORADO

ANONATIONAL FUNGUS COLLECTIONS

PLANT INDUSTRY STATIONo:. BELTSVILLE, MARYLAND

LITERATURECITEO

1. BOYCE, J. S. 1938. Forest pathology. McGraw-Hill,New York. 600 p.

2. ELLIS, J. B., ANO B. M. EVERHART. 1888. New species offungi from various localities. Jour, Myc, 4: 97-107.

3. MEINECKE, E. P. 1929. Quaking aspen, a study in ap-plied forest pathology. U. S. Dept. Agr, Bu!' Tech.155, 33 p.

4. SACCARDO,P. A., ANO P. SYDow. 1899. Saccardo. Syl-loge Fungorum 14, 1316 p.

5. SEAvER, F. J. 1951. The North American cup-fungi(Inoperculates) . F. J. Seaver, New York. 428 p.

6. STARBACK, K. 1895. Discomyceten-Studien. SvenskaVetensk. Akad. Bihang til Handl. Afd. 3, 21(5):1·42.