Stagonospora Blotch of Wheat

Stagonospora Blotch of Wheat


Stagonospora blotch was formerly referred to as glum blotch or Septoria nodorum blotch. The causal organisms of the disease were also listed as incidents of speckled or Septoria leaf blotch. Today it is recognized as a separate disease. Both diseases may occur in the same areas although Stagonospora is favored by warmer temperatures. Yield losses associated with this disease may be as high as 50% in individual fields. The fungi listed as causal organisms are Stagonospora nodorum (Berk.) Castellani & E.G. Germano = Septoria nodorum (Berk.)berk. In Berk. & Broome (teleomorph: Phaeosphaeria nodorum (E. Muller) Hedjaroude) and Phaeosphaeria avenaria (G.F. Weber) O. Eriksson F. sp. triticea T. Johnson (anamorph : Stagonospora avenae (A.B. Frank) Bissett F. sp. triticea T. Johnson) = Septoria avenae A.B. Frank F. sp. triticea T. Johnson. While two fungi are listed as the causal organisms most of the current literature primarily lists Stagonospora nodorum in reference to Stagonospora blotch. Wheat is the primary host but the pathogen is also weakly virulent on barley and rye as well as grasses including Poa and Agrostis spp. The fungus overwinters as mycelium or pycnidia on leaves of cultivated or volunteer wheat and in infected seed at levels as high as 100%. The fungus may also survive in wheat stubble. Infection may occur in spring or fall. Plants arising from infested seed become infected when mycelium grows from the seed to the coleoptile. The fungus is spread via hyphae from the coleoptile to young leaves or pycnidia may be produced on the coleoptile. Primary inoculum in this case consists of conidia (pycnidiospores) which are exuded from pycnidia. These spores are water dispersed or wind blown to susceptible tissue. Conidia from fruiting structures on residue and infected live tissue are disseminated in the same manner. Infection occurs when conidia germinate and penetrate the host directly through stomata. A six-hour period of leaf wetness is required for infection to occur. Seed infection occurs when mycelium grows from infection sites on glumes into the developing seed. Infection may occur in spring or fall with disease development favored by a temperature range of 20-25oC and wet conditions. Inoculum from residue and infected plants is considered the most important source for primary infection where continuous wheat has been grown while infected seed is the most important source in new fields or where a different crop has been used in rotation. Several cycles of the disease may occur when the weather remains wet and temperatures are favorable. Ascospores are produced in pseudothecia during late summer and early fall and serve as inoculum for fall infections. The disease tends to increase in incidence and severity when high levels of phosphorous are present. Researchers have also found that short, early maturing wheat cultivars are more susceptible to Stagonospora blotch than taller, later maturing cultivars. Factors that slow or arrest disease development are hot, dry weather in late spring and summer and fall temperatures that consistently remain below 40oF.

Symptoms


All aerial parts of the plant may be infected. Coleoptiles emerging from infected seed are short and brown. Knob-like swellings may occur with some cultivars and cause the coleoptiles to be distorted. Elongated brown streaks may also be present on the coleoptile. Leaves emerging from plants showing these symptoms may be bent or misshapen. Leaf lesions arising from conidial infection are initially watersoaked. Lesions enlarge and become oval or lens shaped. They dry out, turn brown and are surrounded by a narrow band of chlorotic tissue. Leaf lesions may coalesce as they mature. Pycnidia eventually develop in the spots and are seen as tiny dark brown or black dots. Leaf sheaths and culms may also become infected. Nodes on infected culms become discolored and contain pycnidia. Glume lesions are tan to dark brown in color and linear to oblong in shape. Sunken pycnidia are present in these lesions. Infected seed is shriveled and may have a cracked pericarp. Germination is not affected but yield is reduced as a result of lowered kernel weight.

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.