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United States Department of Agriculture

Agricultural Research Service

Title: Ascochyta Leaf Spot

Authors
item Krupinsky, Joseph
item Cline, Erica

Submitted to: American Phytopathological Society Press
Publication Type: Book / Chapter
Publication Acceptance Date: June 20, 2006
Publication Date: January 31, 2010
Citation: Krupinsky, J.M., Cline, E. 2010. Asochyta leaf spot. p. 18-19. IN: Compendium of Wheat Diseases and Pests, 3rd Edition. Edited by W.W. Bockus, R.L. Bowden, R.M. Hunger, W.L. Morrill, T.D. Murray, and R.W. Smiley. American Phytopathological Society Press, St. Paul.

Interpretive Summary: Ascochyta leaf spot is a plant disease of wheat. It is often overlooked in association with other leaf spot diseases on wheat and is generally of minor economic importance in Europe, Japan, New Zealand, and North America. However, its distribution and frequency may be greater than realized, because Ascochyta species are found on most cereals and grasses throughout the world. Ascochyta leaf spot appears primarily on lower leaves. Fungal structures that appear as black dots may be associated with the leaf spots. Two Ascochyta species are relatively common pathogens of wheat: Ascochyta tritici and Didymella exitialis, the sexual stage of an unnamed Ascochyta species. Leaf spotting is often associated with high humidity, dense foliage, and leaves in contact with soil. Currently, no specific controls are prescribed for Ascochyta leaf spot.

Technical Abstract: Ascochyta leaf spot is a plant disease of wheat. It is often overlooked in association with other leaf spot diseases on wheat and is generally of minor economic importance in Europe, Japan, New Zealand, and North America. However, its distribution and frequency may be greater than realized, because Ascochyta species are found on most cereals and grasses throughout the world. Two Ascochyta species are relatively common pathogens of wheat: Ascochyta tritici Hori & Enjoji and Didymella exitialis (Morini) E. Müll, the sexual stage of an unnamed Ascochyta species. Ascochyta leaf spot appears primarily on lower leaves. The first visible symptoms are chlorotic flecks that develop into distinct, chlorotic, ellipsoidal or round lesions 1-5 mm wide. Later the lesions become diffuse and gray-brown internally and resemble those caused by Stagonospora nodorum. The pathogen sometimes produces pycnidia that appear as black dots within necrotic lesions. Pycnidia are submerged in host tissues except for a papillate projection. Didymella exitialis produces immersed pseudothecia, breaking the surface with small papillate ostioles, dark brown to black, subglobose. The Ascochyta anamorph of D. exitialis produces sparse, scattered, loosely aggregated, yellowish brown, subglobose, ostiolate, immersed to erumpent pycnidia. Conidia (pycnidiospores) are straight, hyaline, guttulate, ellipsoid, with rounded base and apex; and have one median septum. A. tritici apparently persists as mycelium and pycnidia in host residue. Leaf spotting is often associated with high humidity, dense foliage, and leaves in contact with soil. Currently, no specific controls are prescribed for Ascochyta leaf spot.

Last Modified: 4/24/2014
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