Pathogen

• Alternaria spp. and Cladosporium spp.

Hosts

The disease can affect all cereal species although wheat and barley are most commonly affected. The same fungi can cause discolouration of oats.

Symptoms

Symptoms are only visible after harvest. Affected grain shows a darkening of the outer coat particularly at the embryo end of the grain.

Life cycle

The disease is associated with a number of airborne fungi including Alternaria spp. and Cladosporium spp. although the evidence for these fungi actually causing the disease is still limited and is mainly circumstantial. High humidity or frequent rainfall from the milky ripe to soft dough stage and lodging can often trigger infection by these fungi.

Importance

The disease has no significant effect on yield but can have serious implications for the quality of milling wheat, barley and oats for processing. The discolouration of the grain can lead to poor flour and bran colour, and rejection on the basis of discoloured grains. Durum wheat seems to be particularly susceptible.

The disease is commonly reported to be more severe on larger grains, so high specific weight grain can have a higher incidence. This is thought to be due to the larger grains producing a more open floret, allowing fungal spores greater access to the germ end of the grain.