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Research ArticleArticles

A Cylindrosporium Leaf Spot on Oak

Gary P. Munkvold and Dan Neely
Arboriculture & Urban Forestry (AUF) July 1989, 15 (7) 162-164; DOI: https://doi.org/10.48044/joa.1989.15.7.162
Gary P. Munkvold
Section of Botany and Plant Pathology, Illinois Natural History Survey, 607 E. Peabody, Champaign, Illinois 61820
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Dan Neely
Section of Botany and Plant Pathology, Illinois Natural History Survey, 607 E. Peabody, Champaign, Illinois 61820
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Abstract

A Cylindrosporium fungus was consistently associated with and isolated from circular leaf spots on Quercus rubra. It was examined in pure culture and on leaves by light and electron microscopy and identified as C. quercus Sorok. Growth of the fungus in culture was best at 27°C; germination of conidia was best at 24-27°C. Typical symptoms were produced on only 1 of 56 inoculated oak seedlings. This report is the first of C. quercus in Illinois and the first of a Cylindrosporium on Q. rubra.

Leaf spot diseases on trees vary from those that are merely displeasing to those capable of killing trees, usually after two or more consecutive years of premature defoliation. Diseases that defoliate trees in midsummer and permit refoliation late in the growing season are especially harmful to tree health because stored carbohydrates are used inappropriately. Diseases that do not substantially reduce the photosynthetic area of the leaf are primarily of aesthetic importance.

Cylindrosporium is a fungus genus that has been associated with leaf spots on many woody plants, including Shepherdia, Salix, Ulmus, Alnus, Corylus, Robinia, Rhus, Juglans, Morus, Ostrya, Prunus, Betula, Castanea, Fraxinus, Acer, Celtis, Carpinus, and Quercus (10). Although associated with leaf lesions, proof of pathogenicity of the causal fungus has not been established for many tree genera. The leaf spot of cherry, caused by C. lutescens or C. hiemalis (teleomorphs are Coccomyces spp.), has, however, been studied extensively because it is destructive to fruit and may cause tree death (4,5).

In Illinois, Cylindrosporium spp. have been found on pin, shingle and California black oak (1, 7). In other states, Cylindrosporium spp. have been reported on white, bur, Oregon, and live oak (2, 9). The only report of C. quercus in the United States was on an oak species from Ohio (6). The objectives of this study were to describe the observed Cylindrosporium leaf spot on oaks, to characterize the associated fungus, and to prove pathogenicity of the fungus.

Materials and Methods

The Cylindrosporium isolates used in this study were obtained in pure culture by placing small sections of diseased leaf tissue on potato dextrose agar (PDA) or by placing necrotic leaf lesions in moist chambers for 24 hours and transferring the fungus cirrhi onto PDA in culture dishes. The fungus isolates were then placed on four agar media (PDA, prune juice agar, corn meal agar, and V-8 juice agar) to determine the best medium for growth. Fungus isolates on agar media were also incubated at 18, 21, 24, and 27°C to determine the optimum temperature for growth. Conidia from the isolates were incubated at the same temperatures to determine optimum temperature for spore germination.

The genus and species of the associated fungus were determined by examining the fruiting structures and the conidia. Freehand sections through the leaf lesion were examined with a light microscope. Specimens of diseased leaf tissue were also prepared for scanning electron microscopy and photographed. Characteristics of the fungus in culture were also observed.

Pathogenicity of the fungus was tested by inoculating potted seedlings of northern red (Q. rubra) and scarlet oak (Q. coccinea) with spore suspensions from PDA cultures or from acervuli on lesions of diseased leaves. The spores were brushed or sprayed onto injured and noninjured leaves and covered with plastic bags for 48 hours. Leaves were observed for lesion development in the greenhouse for 3 months.

Results and Discussion

The Cylindrosporium studied here was first collected from northern red oak in Urbana and Lisle, Illinois, in 1985. The disease was present on red oak in 1986, 1987, and 1988, and found at least once on English oak (Q. rober) and on bur oak (Q. macrocarpa). The lesions were first evident in July or August. Only on one red oak was it sufficiently serious to cause extensive defoliation on lower branches, an effect that resulted in branch dieback the following year.

The leaf spots associated with this fungus are dark brown when small and later became light tan with a dark margin. The spots are roughly circular in shape and may be surrounded with a yellowed halo (Fig. 1). Spots average 2.3 mm in diameter but are commonly as large as 3.5 mm and range up to 6 mm. They are spread randomly over the leaf surface and rarely coalesce. Each spot typically has one acervulus located in the center of the lesion on the abaxial surface. Occasionally spots have several acervuli. Acervuli appear yellow-orange in color, are pulvinate, subcuticular and erumpent and exude a gelatinous mass containing many conidia. Acervuli are 200-300 μm in diameter. Conidiogenous cells are phialidic, cylindrical, unbranched, and hyaline. Conidia are hyaline and filiform or cylindrical, sometimes nearly falcate, 18-35 x 3-4 jum and 0-3 septate. No sexual fruiting structures were observed.

Figure 1.
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Figure 1.

Cylindrosporium quercus. (A) Photomicrograph of conidia. (B) Scanning electron micrograph of acervulus. (C) Typical lesions. (D) Northern red oak leaf with typical lesions. (E) Scanning electron micrograph of acervulus and epidermal fragment forced up by emerging conidia. (F) Photomicrograph of cross section through the acervulus. (G) Scanning electron micrograph of conidia showing the flattened basal scar.

The fungus isolated from oaks in Illinois belongs to the species Cylindrosporium quercus Sorok. (8, 9). It grows very slowly in culture but somewhat faster on PDA than on the other media tested. Growth averaged 12 mm per week at the optimum temperature of 27°C. Seventy percent of the conidia produced germ tubes within 24 hours at 24 and 27°C.

Unfortunately, pathogenicity of C. quercus on oak was not proven conclusively. Of the 56 trees inoculated throughout the study, only 1 northern red oak developed the characteristic leaf spot, which appeared 11 weeks after inoculation. This tree developed six spots on three leaves, all with typical acervuli and conidia. No scarlet oaks developed disease symptoms.

A second leaf disease caused by the fungus Tubakia dryina (Actinopelte dryina) (3) is occasionally found associated with the Cylindrosporium lesions. It seems likely that Cylindrosporium is the primary invader, with Tubakia invading the stressed tissue near the Cylindrosporium lesion. The Cylindrosporium lesion then becomes greatly enlarged and contains numerous Tubakia fruiting structures.

Footnotes

  • ↵1 This project was funded in part through a J.B. Turner Scholarship, College of Agriculture, University of Illinois at Urbana-Champaign.

  • © 1989, International Society of Arboriculture. All rights reserved.

Literature Cited

  1. 1.↵
    1. Carter, J.C.
    1941. Preliminary investigation of oak diseases in Illinois. Illinois Natural History Survey Bulletin 21:195–230.
    OpenUrl
  2. 2.↵
    1. Ellis, J.B. and
    2. B.M. Everhart
    . 1987. New species of North American fungi from various localities. Bulletin Torrey Botanical Club 24:277–328.
    OpenUrl
  3. 3.↵
    1. Glawe, D.A. and
    2. J.L. Crane
    . 1987. Illinois fungi XIII. Tubakia dryina. Mycotaxon 29:101–112.
    OpenUrl
  4. 4.↵
    1. Heald, F.D.
    1933. Manual of Plant Diseases. Second edition. McGraw-Hill, New York. 953 pp.
  5. 5.↵
    1. Higgins, B.B.
    1914. Contribution to the life history and physiology of Cylìndrosporium on stone fruits. American Journal of Botany 1:145–173.
    OpenUrl
  6. 6.↵
    1. Martin, G.H.
    1920. Diseases of cotton, sugar cane, forest trees, ornamentals, and miscellaneous plants in the United States in 1919. Plant Disease Reporter Supplement 11:274–306.
    OpenUrl
  7. 7.↵
    1. Nance, N.W.
    1939. Diseases of plants in the U.S. in 1938. Plant Disease Reporter Supplement 119:119–289.
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  8. 8.↵
    1. Saccardo, P.A.
    1985. Cylìndrosporium quercus Sorok. Sylloge Fungorum 11:574.
    OpenUrl
  9. 9.↵
    1. Sorokin, N.V.
    1886. Rastite’ nye Parazity chelovieka 1 Zhnivotnykh, kak prichina zaraznykh’ bolieznei, volume 4. St. Petersburg. 646. pp.
  10. 10.↵
    1. Weiss, F.
    1960. Index of plant diseases in the United States. U.S. Department of Agriculture Agriculture Handbook #165. U.S. Government Printing Office, Washington, D.C. 531 pp.
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A Cylindrosporium Leaf Spot on Oak
Gary P. Munkvold, Dan Neely
Arboriculture & Urban Forestry (AUF) Jul 1989, 15 (7) 162-164; DOI: 10.48044/joa.1989.15.7.162

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A Cylindrosporium Leaf Spot on Oak
Gary P. Munkvold, Dan Neely
Arboriculture & Urban Forestry (AUF) Jul 1989, 15 (7) 162-164; DOI: 10.48044/joa.1989.15.7.162
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