Leaf and Glume Blotch

Pathogen

Phaeosphaeria nodorum (Stagonospora nodorum formerly Septoria nodorum)

Hosts

The disease mainly attects wheat, but occasionally barley and rye.

Symptoms

S. nodorum can be seed borne and infect seedlings, resulting in water-soaked, dark green areas on the coleoptile, later becoming necrotic. Twisted, distorted and stunted seedlings may also occur. On mature leaf tissue the first symptoms of infection are small necrotic lesions.  Later these develop into brown oval lesions surrounded by a chlorotic halo.  These lesions frequently coalesce to produce large areas of dead, dry and sometimes split tissue. Pycnidia form within affected tissue, but these are a pale pinkish brown colour and difficult to see in the field, even with a hand lens. They are best seen by viewing the lesions in transmitted light with a hand lens. S. nodorum can also infect the ears, particularly of wheat, causing glume blotch.  Dark brown patches like burn-marks develop on the glumes, which later become purple-brown. Glume blotch symptoms are easiest to see on green ears.

Although more usually associated with necrotic blotching of leaves and glumes, S. nordorum can cause post-emergence seedling blight in cool wet soils.

Life Cycle

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Septoria nodorum survives as dormant mycelium, and as pycnidia and pseudothecia on seed, stubble, debris, autumn-sown crops and volunteers. In the absence of crop debris, initial infections in the autumn or spring may result from wind-borne ascospores released from pseudothecia long distances away. As temperatures rise and humidity increases pycnidiospores are produced from the pycnidia. These are splash-dispersed up the infected plant and from plant to plant. Temperatures of 20-27°C, together with 100% relative humidity, are optimal for spore production and germination and a period of rain is essential for spore dispersal. The disease cycle can be completed in 10-14 days during such conditions. Spores produced from pseudothecia and pycnidia, which develop on the flag leaf and ear at the end of the season, can initiate infection in early autumn-sown crops and volunteers and may also remain dormant for the winter. Glume blotch infection of the ear can lead to infection of the seed.

Like the Fusarium spp., S. nodorum can survive on seed or plant debris. While trash-borne inoculums is usually more important in initiating the later phases of the disease (leaf and glume blotch), fungus carried on the seed is more likely to be responsible for septoria seedling blight.

Importance

S. nodorum was once the most serious pathogen on cereals in the UK, although it now rarely causes significant losses except in wet seasons in the south west of England. Yield losses up to 50% have been reported in trials although average annual losses in the UK probably do not exceed 3%. Losses caused by septoria seedling blight are generally not significant.

Cultural control

Disposal of crop debris by ploughing can help prevent early infection. Few varieties are particularly susceptible.

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