Identifying wheat and barley seed affected by fusarium head blight

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Seed symptoms mistaken for fusarium head blight

Wheat

a) 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 FHB. This type of fungal growth is frequently that of Septoria nodorum or one of the fusaria.

b) 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.

c) 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 FHB. 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

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

e) 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 FHB, this discolouration is internal, and cannot be scraped off the seed.

f) 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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