Pathogen 

• Fusarium spp. and Microdochium nivale

Hosts

The disease infects wheat, barley, oats, triticale and grasses.

Symptoms

There are many species of Fusarium that affect cereals. These fungi form a complex of diseases on seeds, seedlings and adult plants. The seed-borne pathogen Microdochium nivale (formally known as Fusarium nivale) is also usually included in this group of fungi.

M. nivale is the primary pathogen in the group which causes seedling blight resulting in seedling death and thinning of the plant stand. Other species cause a range of symptoms including brown lesions on stem bases, often restricted to outer leaf sheath. Fusarium lesions often begin in the leaf sheath at the stem base where crown roots split the leaf sheath when emerging. This infection can then spread up the leaf sheath causing long dark brown streaks at the stem base. The most commonly seen symptom in the UK is the dark brown staining of the lower nodes. On older plants Fusarium infection can produce a true foot rot, where the stem base becomes brown and rotten, resulting in lodging and white-heads. This symptom is less common in the UK, although it can be found in very dry seasons.

Many of the Fusarium species cause a range of symptoms - often termed ear blights. F. culmorum and F. graminearum are the most commonly found species in the UK. Other species include F. avenaceum, F poae and F. langsethiae. Infection frequently results in the whole or part of the ear becoming bleached. This symptom is seen when ears become infected during the early flowering stages. Later infections may result in infection of the grain but without obvious bleaching of the ears. The ear blight phase of the disease can cause yield loss but is most important as it can result in mycotoxin production in the grain. Mycotoxins are substances toxic to animals and humans. Levels in grain, flour and flour products for human and animal consumption are limited under EU legislation. See HGCA 'Guidelines to minimize risk of fusarium mycotoxins in cereals' for more details.

Life cycle

The most important source of Fusarium for wheat crops is the seed but the fungus can also survive on debris in the soil. In seasons where weather conditions are wet during flowering and grain formation, spores are splashed from lower in the canopy causing ear blights and seed-borne infection. In such seasons seed-borne infection can pose a serious threat to crop establishment unless seed is treated to control Fusarium. All the cereal Fusarium species are common in soil. Most have competitive saprophytic abilities which allow them to colonise debris and stubble in soil. Volunteers may also act as a source of inoculums.

Importance

Symptoms of Fusarium infection are common in wheat crops in the UK and most cereal crops will have some symptoms of one or other of these diseases. When weather conditions are wet during flowering, high levels of ear blight can occur but their incidence is frequently over-estimated and losses are only rarely serious. Severe foot rotting is very rare in the UK and losses are generally very small. The seed-borne phase of the disease is potentially very damaging. Seed treatment plays a major role in preventing seedling losses in wheat. Seedling blight is rare in barley.