Black Chaff of Wheat

Black Chaff of Wheat


Black chaff, also referred to as bacterial stripe or bacterial streak is the most common bacterial disease of wheat. Yield losses associated with the disease range from a trace to 40%. Black chaff is generally more severe in humid climates but may also increase when overhead irrigation is used. The causal organism is Xanthomonas campestris pv. translucens (Jones et. al. ) Dye. Barley, rye, triticale and many grasses are also listed as hosts of the pathogen, but different strains vary in their ability to infect these plants. The bacterium overwinters on (and occasionally in) infected seed up to 5 years and on crop debris. Survival in the soil is also suspected but not proven conclusively. The pathogen is disseminated on infected seed, by splashing water (rain or irrigation), plant contact, and insects. Severe epidemics can occur when a small portion of the seed lot is infected if optimum environmental conditions exist. The bacterium enters the host through stomata or wounds. It multiplies in tissue creases and intercellular spaces that contain free water. Although water plays an important role in pathogen dissemination and disease development, free water may not be necessary for infection to occur. Once established, X. campestris pv. translucens multiplies and cells are exuded from the host in a slimy mass. Secondary infection occurs when environmental conditions are favorable. Wheat plants may support the bacterium as an epiphyte and not develop symptoms. These plants as well as wild grasses serve as reservoirs of secondary inoculum. Optimum growth of the pathogen on artificial occurs at 28-30oC. The most severe epidemics in the field develop when frequent rains occur during heading.

Symptoms


Symptoms may occur at most stages of development but are most evident after heading. All aerial structures may be infected. The disease gets its name from symptoms seen on glumes (chaff). Infected tissue is initially water-soaked. Dark brown to black necrotic blotches or streaks are visible on the glumes. The upper part of the glume is discolored in most cases but the entire structure may become discolored. Awns initially turn brown at their base then exhibit irregular brown patches or alternating bands of healthy and discolored tissue. Seed which develops on affected heads may appear healthy or be shrunken near its base. Affected seed may lose its ability to germinate. When the disease becomes severe early in the season heads are spongy, sticky, and sterile but are not discolored. Leaf symptoms also begin as water-soaked lesions. A lime-green halo may be present around the lesion. The infected areas appear as streaks on barley, rye and triticale and as spots or wheat. Affected areas coalesce and become necrotic. In severe cases, the entire leaf is blighted. All types of infected tissue may display droplets of yellowish bacterial slime during periods of wet weather or high humidity. The droplets are viscous when wet and become crystalline and scale-like when the weather turns dry.

Plant Health Management

References

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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. John Watkins, 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.