Life cycle and symptoms of fusarium and microdochium in cereals

This disease complex can be seedborne, soilborne or trashborne. Learn about the life cycle and the main symptoms associated with infection in cereals.

There are many fungal pathogens in this disease complex, including: Fusarium avenaceum, F. culmorum, F. graminearum, F. poae, F. langsethiae, Microdochium nivale and M. majus.

The complex can form on seeds, seedlings and adult plants.

Infection can result in a range of symptoms on cereals (wheat, barley, oats, rye and triticale) and grasses.

Seedling blight is associated with pre- and post-emergence damping off and can impact crop establishment.

Infected seedlings may die and survivors may develop a brown lesion near the soil, which can eventually lead to foot and root rot.

Symptomless infections can also occur.

Each species has a specific temperature requirement for infections, for example:

• Microdochium seedling blight is most severe in cool and wet soils
• Fusarium seedling blight is most severe in warmer and drier soils

Notes

The seedborne pathogens M. nivale and M. majus were formerly known collectively as Fusarium nivale. M. nivale is the primary pathogen in the group that causes seedling blight, which also causes snow mould.

Foot rot infections become obvious from late stem extension onwards.

Symptoms include dark-brown staining of the lower nodes. Long dark streaks may also appear at the stem base.

Infection can also lead to a true foot rot on older plants, where the stem base becomes brown and rotten, resulting in lodging and whiteheads.

This symptom is rare in the UK but it can develop in very dry seasons.

Note

The foot rot symptoms associated with Fusarium spp are similar to those caused by Cochliobolus sativus (Drechslera sorokiniana).

Fusarium species also cause many symptoms on the ear.

In the UK, the most common fusarium species are Fusarium culmorum and F. graminearum (which also mainly produce the key mycotoxins DON, NIV and ZON).

Primary infection by fusarium is from infected seed, soil, crop debris and volunteers or host weed species.

Spores from seedling blight or foot rot lesions, which can be splashed up the plant or move from leaf to leaf, are the main source of ear blight infection.

Although spores of some fusarium species are also spread by the wind, this is not an important infection source.

Ear blight infection occurs during flowering, which is favoured by warm, wet and humid conditions*.

Bleached ears often show above the point of infection around the milky ripe stage (GS 75), unless relatively late infection occurred (which may be associated with no obvious bleaching).

The presence of orange/pink fusarium spores may also be visible on infected spikelets.

Further rainfall and humid conditions encourage fungal growth, secondary infection and mycotoxin production.

As the crop ripens, symptoms become less visible.

At harvest, fusarium ear blight can result in shrivelled grains with a chalky white or pink appearance, although this is not always the case.

Notes

*T-2 and HT-2 mycotoxins are produced by fusarium species that are favoured by drier conditions, such as F. langsethiae. Therefore, risk factors are different to those for DON/ZON.

Microdochium nivale and M. majus do not produce mycotoxins.

Figure 1. Fusarium and microdochium life cycle