Stegophora ulmea

Symptoms of black spot on elm in the summer.
Symptoms of black spot on an Elm leaf in the fall.

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Stegophora ulmea
Scientific classification
Kingdom: Fungi
Phylum: Ascomycota
Class: Sordariomycetes
Subclass: Sordariomycetidae
Order: Diaporthales
Family: Gnomoniaceae
Genus: Stegophora
Species: S. ulmea
Binomial name
Stegophora ulmea
(Fr.) Syd. & P. Syd., (1916)
Synonyms

Asteroma ulmeum (Miles) B. Sutton, (1980)
Cylindrosporella ulmea (Miles) Arx, (1957)
Dothidella ulmi (Fr.) Ellis & Everh., (1892)
Gloeosporium ulmeum Miles, (1921)
Gloeosporium ulmicola Miles [as 'ulmicolum'], (1921)
Gnomonia ulmea (Fr.) Thüm., (1878)
Lambro ulmea (Fr.) E. Müll., (1962)
Sphaeria ulmea Fr., (1823)
Xyloma ulmeum Schwein., (1822)

Stegophora ulmea is a foliar disease of elms commonly known as black spot of elm, twig blight, and elm leaf scab.[1] It is characterized by yellow spots that become black spots on the leaves. The pathogen is an ascomycete fungus native to North America. Stegophora ulmea is its teleomorph name.[2] It has two anamorph names, Gloeosporium ulmicolom referring to the macroconidia stage and Cylindrosporella ulmea referring to the microconidia stage.[1] This pathogen was formerly known as Gnomonia ulmea[3].

Hosts and Symptoms

S. ulmea infects all Ulmus species and Japanese zelkova.[2] It is most virulent on American white elm, Ulmus Americana[1]. Other elms it is known to infect include:[1]

S. ulmea is characterized by chlorotic yellow spots 1 millimeter in diameter with a black center that develop early in the spring.[1][2][4] They darken and become raised. The black center can increase to occupy the entire chlorotic area.[4] The black spots can become about 5 millimeters in diameter.[1] As the season continues, the tissue around the original spot may become necrotic.[4] In severe cases of the disease there is premature shedding of leaves, blight of young leaves and shoots, and complete defoliation early in the fall.[1] Fruits that are infected become crumpled.[1] Infection of mature trees is rarely fatal.[1][2]

Disease cycle

In the spring, new leaves are infected with ascospores which develop from the survival structure, perithecia, found in leaf debris.[1] It is thought that inoculum from overwintered buds can also result in infection.[1][4] The perithecia are the structure in which S. ulmea survives the winter. Ascospore release is synchronized with the foliar development of the elms.[4] Ascospores commonly infect lower leaves and leaves near the bud.[1] A period of wetness and dryness with a temperature over 7 degrees Celsius is required before ascospores are released.[1] The ascospores disperse through the air and have the potential to travel over long distances.[1] Acervuli develop in the center of the lesions.[1] Acervuli can release macroconidia, which are white.[1] They mature 10–20 days after infection.[1] During spring and early summer, the macroconidia act as a secondary inoculum. This is the asexual part of S. ulmea’s life cycle.[1] Water is necessary for the dispersal of the macroconidia.[1] Microconidia are produced in the lesions during midsummer.[1] They act as spermatia in the sexual stage of the S. ulmea’s life cycle.[1] During late summer and fall perithecia, the sexual structure, begins to develop.[1]

Control

Sanitation, or removal all leaf debris seems to be the best method of control.[1] In commercial growing arenas, it is suggested that overhead watering should not be used, because it helps spread the pathogen.[1] Resistance greatly varies between species.[1] U. thomasfi seems to be the most resistant.[4] The majority of elms seem to be tolerant.[4] A dominant gene conferring resistance to U. parvifolia was discovered, though it did not provide absolute resistance.[5] There is currently no information about fungicides used to control this disease.[1] This disease is not typically fatal and is not actively addressed.[3] Aeration seems to moderately reduce growth and sporulation.[6] Cool temperatures and high humidity enhance the disease, so avoidance of these conditions will decrease the prevalence of disease.

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 "Stegophora ulmea" (PDF). Ltd. European and Mediterranean Plant Protection Organization. Blackwell Publishing. 2005.
  2. 1 2 3 4 Lane, Reed, Matthews-Berry (2013). "Rapid pest risk analysis for stegophora ulmea" (PDF). The Food and Environment Research Agency. Retrieved 1 December 2016.
  3. 1 2 "Elm diseases". Penn State college of agricultural sciences. Penn State Extension. 2016.
  4. 1 2 3 4 5 6 7 McGranaham G. H. (1982). "Stegophora ulmea (Schwanniomyces: Fries) sydow & sydow: biology and host resistance". The University of Wisconsin Madison, Porquest Dissertations Publishing.
  5. ↑ Benet. H., guries R., Boury, S., Smalley E. (1995). "Identification of RAPD markers linked to a black leaf spot resistance in Chinese elm". Theor Appl Genet. 90: 1068–1073.
  6. ↑ McGranahan G.H., Smalley E.B. (1984). "Conidial morphology, axenic growth and sporulation of stegophora ulmea". Phytopathology.
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