Identifying wheat and barley seed affected by fusarium head blight

Photographic guide to identifying wheat and barley seed affected by fusarium head blight and seed symptoms mistaken for fusarium head blight.

  • Fusarium head blight

    Fusarium head blight

    Fusarium head blight is a fungal disease of small grain cereals. In North America, the three species of fungus most often responsible for the disease are Fusarium avenaceum, F. graminearum, and F. culmorum. F. graminearum and F. culmorum may produce a number of fungal toxins, called mycotoxins, in the grain. The most commonly produced mycotoxin is deoxynivalenol, also known as vomitoxin. Economic losses from fusarium head blight arise from yield and grade reductions as well as problems associated with the presence of mycotoxins.

    In wheat, subsceptibility to fusarium head blight peaks at flowering and declines as the grain matures. Durum wheats are more susceptible to fusarium head blight than are the common wheats. Fusarium infection occurs only if there is precipitation during the period of susceptibility. Early infection results in shriveled, chalky white seeds or sterile florets. Many of the shriveled, light seeds are lost during combining, although some may remain in the harvested grain. Those seeds remaining are referred to as fusarium damaged kernels or fusarium damaged kernels in Canada and scabby kernels in the United States. The grading systems in Canada and the U.S. allow only a small number of fusarium damaged kernels in grain destined for milling and other human uses.

    In barley and oats, symptoms of fusarium head blight are often difficult to find. In most years, few infected seeds display the fungal sporodochia or perithecia which are typical symptoms of seed infection in these crops. The symptoms become more common during wet harvests. Blackpoint is often present on barley seeds affected by fusarium head blight, but the resulting discolouration is not specific to Fusarium. Blackpoint is also associated with infection by Helminthosporium sativum, a cause of common root rot. Deoxynivalenol, often associated with fusarium damaged kernels, is one of the milder mycotoxins. Non-ruminants, such as hogs, are the most sensitive to the presence of deoxynivalenol in their diets. A typical response is reduced feed consumption resulting in slower weight gain. The presence of detectable amounts of deoxynivalenol in a barley sample can lead to its rejection as malting barley.

    Monitoring

    Since 1984, when a few fields in southeastern Manitoba were found to have high levels of fusarium damaged kernels caused by F. graminearum, researchers at the Grain Research Laboratory have been monitoring grain samples from western Canada for the presence of fusarium damaged kernels and identifying the fungal species responsible. The fungal species of most concern is F. graminearum, an aggressive pathogen and a capable deoxynivalenol producer. F. graminearum appears to have spread westward from southern Manitoba, and is now an important pathogen in Manitoba and eastern Saskatchewan. However, it is only at very low levels outside of this area.

    Presence of fusarium damaged kernels is not always associated with the presence of deoxynivalenol, but depends upon which species produced the fusarium damaged kernels.

    Definitions

    DON (Deoxynivalenol)
    The mycotoxin most commonly produced by some of the fungal species which cause fusarium head blight. Also known as vomitoxin.
    FDK
    Fusarium damaged kernels. They are called scabby kernels in the U.S.
    FHB
    Fusarium head blight. This fungal disease of small grain cereals is caused by several species of Fusarium. In North America, the three species most often responsible for the disease are F. graminearum, F. culmorum, and F. avenaceum.
    Mycelium
    A fibrous, thread-like mass of fungal growth.
    Perithecia
    Bluish black fungal structures that produce a spore called an ascospore. The presence of these structures on the seed indicates that the seed was infected by F. graminearum.
    Pycnidia
    Small, black, spore-producing structures produced by a variety of fungi. The spores formed in these structures are called pycnidiospores. Pycnidia are not formed by Fusarium species.
    Sporodochia
    Masses of fungal spores. In Fusarium species they are typically orange. The spores in these frequently slimy masses are called conidiospores. All Fusarium species that cause fusarium head blight produce sporodochia.
  • Fusarium head blight on wheat

    Fusarium head blight on wheat

    Fusarium head blight on wheat, Orange sporodochia

    Fusarium head blight on wheat, Orange sporodochia are formed at the base of the glumes, as shown. Infected spikelets ripen prematurely.

    Fusarium head blight on wheat. Bluish black perithecia

    Fusarium head blight on wheat, Bluish black perithecia are occasionally formed on the head.

    Red Spring

    Red spring wheat, left to right, Sound red spring wheat seed, Not a Fusarium Damaged Kernel, FDK with light symptoms, FDK with severe symptoms

    From left to right

    Sound red spring wheat seed.

    Not a Fusarium Damaged Kernel. This seed does not have sufficient seed discolouration or fibrous fungal growth, also called mycelial growth, to qualify as a fusarium damaged kernel according to the Canadian Grain Commission Official Grain Grading Guide

    Fusarium damaged kernels with light symptoms. Mycelial growth is visible around the germ and in the broad crease, and the seed looks shriveled and chalky white.

    Fusarium damaged kernels with severe symptoms. Abundant mycelial growth is visible on both seed surfaces, with some pink discolouration at the germ. The seed has a shriveled, chalky white appearance.

    Amber Durum

    Amber Durum, Sound durum wheat seed

    Sound durum wheat seed.

    Amber Durum, Moderate symptoms of FDK

    Moderate symptoms of fusarium damaged kernels. Mycelial growth is visible at the germ and crease. Other symptoms are the wrinkled seed coat, broad crease and bronzy colour.

    Amber Durum, Severe symptoms of FDK

    Severe symptoms of fusarium damaged kernels. Mycelial growth is abundant, the seed coat is wrinkled, the crease is broadened, and the colour is bronzy.

    Prairie Spring

    Prairie Spring, Sound Canada Prairie Spring Red wheat seed

    Sound Canada Prairie Spring Red wheat seed.

    Prairie Spring, Moderate symptoms of FDK

    Moderate symptoms of fusarium damaged kernels. Mycelial growth is visible at the germ and crease. Other symptoms are a wrinkled seed coat, a broad crease and a chalky white appearance.

    Prairie Spring, Severe symptoms of FDK

    Severe symptoms of fusarium damaged kernels. Abundant mycelial growth is found at the germ and crease. The seed coat is wrinkled, the crease is broadened, and the appearance is chalky white with pink at the germ.

    White Winter

    White Winter, Sound white winter wheat seed

    Sound white winter wheat seed.

    White Winter, Moderate symptoms of fusarium damaged kernels

    Moderate symptoms of fusarium damaged kernels. Mycelial growth is visible at the germ and crease. Other symptoms are a wrinkled seed coat, a broad crease and a whitish colour.

    White Winter, Severe symptoms of fusarium damaged kernels

    Severe symptoms of fusarium damaged kernels. The seed coat is wrinkled, the crease is broadened, and the appearance is pink and chalky white.

  • Fusarium head blight on barley

    Fusarium head blight on barley

    Fusarium head blight on barley

    Fusarium head blight on barley. Symptoms on barley heads are more subtle than on wheat. Orange sporodochia may be seen at the base of infected florets as well as some dark discolouration. Heads occasionally have perithecia present.

    Sound hulless barley seed.

    Sound hulless barley seed.

    Hulless light symptoms

    Hulless with light symptoms. Mycelial growth is visible in the crease and the germ. The perithecia and sporodochia characteristic of fusarium head blight in covered barley are absent in hulless barley because of removal of the hull where these structures are normally found. In this respect, damaged kernels of hulless barley more closely resemble fusarium damaged kernels of wheat.

    Hulless moderate symptoms

    Hulless with moderate symptoms. Mycelial growth is more apparent, with some dark discolouration of the seed and reduced seed size.

    Hulless severe symptoms

    Hulless with severe symptoms. Seeds are thin, with some dark discolouration and abundant mycelial growth.

    Sound barley seed

    Sound barley seed.

    Sound barley seed Black perithecia

    Black perithecia. Bluish black perithecia encrust the seed surface. The dark discolouration of this seed and the seed in the next image is also typical of infection of barley seed by fusaria and other pathogens.

    Sound barley seed Orange sporodochia

    Orange sporodochia. These orange spore masses may be formed by a number of Fusarium species, some of which do not produce deoxynivalenol.

  • Seed symptoms mistaken for fusarium head blight

    Seed symptoms mistaken for fusarium head blight

    Wheat

    Wheat Midge damage with mould

    Midge damage with mould. Feeding by the larva of the orange wheat blossom midge can result in shrunken, misshapen seeds. Depending upon the growing conditions, midge-damaged seeds may become visibly mouldy. A whitish fungal mycelia can result in seeds similar in appearance to seeds formed as a result of fusarium head blight. This type of fungal growth is frequently that of Septoria nodorum or one of the fusaria.

    Wheat Asteromella species

    Asteromella species. This fungus is recovered from seeds with a somewhat chalky appearance and visible mycelial growth. The seeds characteristically have an orangish translucence and black pycnidia on the surface, frequently at the brush end. In culture, Asteromella sp. grow very quickly and form a dense, white mycelial growth.

    Wheat Septoria nodorum

    Septoria nodorum. Infection of the seed by this fungus, which causes glume blotch in wheat, can result in a seed visually indistinguishable from those formed by fusarium head blight. This type of seed appears primarily in Saskatchewan and Alberta durum wheat. However, no samples yet examined have shown a great number of these seeds present.

    Barley

    Barley Fungal pycnidia

    Fungal pycnidia. These pycnidia are smaller and more discreet than the perithecia of F. graminearum.

    Barley Helminthosporium

    Helminthosporium species. The net blotch fungus Helminthosporium teres (and sometimes the leaf stripe fungus H. graminea) is frequently recovered from barley seeds that display an orange discolouration at the basal end. Unlike the discolouration of sporodochia associated with fusarium head blight, this discolouration is internal, and cannot be scraped off the seed.

    Barley Sooty moulds species

    Sooty moulds. The dark, sooty moulds, usually species of Alternaria and Cladosporium, present on barley seed in years of wet harvests may be mistaken for perithecia. The sooty moulds, however, are fibrous and easily scraped off.

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