Pyrenophora teres

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Pyrenophora teres conidia (click on image to enlarge it)
Author(s): A.R. McTaggart, Department of Primary Industries and Fisheries
Source: PaDIL

Pyrenophora teres Drechsler 1923

The fungus causes barley net blotch, a serious disease in temperate regions. It can also infect other cereals. The symptoms are characterized by dark brown leaf streaks, often arranged in a net-like pattern (net form). A different variety of the fungus causes dark brown oval spots (spot form). The lesions are usually bordered by a chlorotic halo. Yield losses of up to 50% have been estimated. The spores disperse through rain and wind. The fungus can be also transmitted through seeds.

Pyrenophora teres hilum of conidium (click on image to enlarge it)
Author(s): A.R. McTaggart, Department of Primary Industries and Fisheries
Source: PaDIL

Infections are promoted by cool (10-15°C) and rainy conditions and often start at the older leaves. When conidia are formed, the fungus spreads to younger leaves. The fungus persists in plant debris (as mycelium or pseudothecia) and in volunteer barley plants. The main options for management are crop rotation, resistant cultivars and deep ploughing to remove infected debris.

The conidia are cylindrical with rounded ends, approximately 80-150 µm long and about 20 µm wide. They have 4-6 pseudosepta and a hilum at the base which is about 5 µm broad (see image at left). The fungus goes through sexual reproduction in autumn when pseudothecia are formed. These are 1-2 mm large with black spines around their openings. Ascospores are elliptical, light brown and about 50-60 x 20-25 µm large with 3-4 septa. They are restricted at the septa.

Pyrenophora teres f.sp. teres - causes net lesions and is the more common form
Pyrenophora teres f.sp. maculata - causes spot lesions

Vernacular names
• Deutsch: Netzfleckenkrankheit der Gerste
• English: barley net blotch
• Español: mancha reticular de la cebada
• Français: rayure réticulée de l'orge
maladie des stries foliaires de l'orge


Synonyms:
Drechslera teres (anamorph synonym)
Helminthosporium teres
Pyrenophora trichostoma

For a review see Liu et al., 2011.