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Discolorations and Pathogens Associated with Wheat Kernels (05/04/17)

Small grain planting season is in full swing and several questions pertaining to discolored wheat seed lots have been asked over the past few weeks.

Discolorations and Pathogens Associated with Wheat Kernels

Small grain planting season is in full swing and several questions pertaining to discolored wheat seed lots have been asked over the past few weeks. There can be several causes of kernel discolorations and this article will address some of the common pathogens that can be associated with a wheat seed lot.

Red Smudge (Figure 1b.) – Red smudge (caused by the tan spot pathogen) is characterized by a reddish discoloration of the seed coat and tends to be more common in durum. Kernels remain relatively plump as opposed to kernels infected with Fusarium.

Scabby Seed (Figures 1c and 2b) – Fusarium head blight (scab) results in yield and quality losses in the field. This disease also increases the presence of Fusarium infected kernels (scabby seed). Scabby seed tends to be chalky, pink, shriveled and lifeless. However, late season Fusarium infections during grain development may leave kernels asymptomatic, and still harbor the Fusarium pathogen. When seeded, Fusarium infected kernels will increase the risk for seedling blight and root rot.

Black Point (Figures 1d and 2c) – As the name implies, black point refers to a brown to black discoloration observed on the embryo of the seed extending down the kernel. This common kernel discoloration is caused by an assortment of fungi including the pathogen responsible for common root rot (Cochliobolus sativus) as well as saprophytic fungi (Cladosporium sp. and Alternaria sp.) associated with sooty mold of wheat heads.

Common Bunt (Figure 2d) – Common bunt can be identified using the human senses of sight and smell. Infected kernels tend to look dull gray-green and be filled with black dusty spores. Grain lots with noticeable amounts of common bunt will have a fishy-odor.

Ergot (Figure 2e) – Ergot bodies (sclerotia) are black to purple irregularly shaped fungal structures. Ergot bodies can resemble the size of a kernel or be 2-4 times larger. When ergot bodies are split open, a white interior will be observed.

Loose Smut (Figure 3) – Loose smut is one of the most common seed borne diseases in North Dakota. There are no kernel discolorations associated with loose smut and germination rates will be normal. The fungus remains in the embryo of the kernel and grows systemically with a developing plant. When a wheat spike emerges from a leaf sheath, the spike will be replaced with dusty black spores and no kernels will develop. Winds will displace the spores on the head leaving an empty rachis.

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Pest Management

Seed-borne pathogens and pathogens associated with wheat seed lots can be managed using several tools, however not every tool is applicable for every pathogen. The use of certified seed will drastically reduce the risk of seed-borne pathogens. If using a bin-run seed source, be aware of any potential pathogens that could impact germination and stand establishment. Cleaning can have a significant impact on lowering the amount of Fusarium infected kernels and can help reduce the occurrence of ergot bodies. Fungicide seed treatments are extremely effective for managing loose smut and common bunt, and can help suppress seedling blights and root rots caused by Fusarium and Cochliobolus. On the other hand, fungicides are not recommended for managing ergot. For more information on seed treatments, please consult the 2017 North Dakota Field Crop Plant Disease Management Guide PP622.

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Andrew Friskop

Extension Plant Pathology, Cereal Crops

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