Gaeumannomyces graminis

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Gaeumannomyces graminis hyphae on Cynodon dactylon (click on image to enlarge it)
Author(s): Kevin Ong, Texas AgriLife Extension Service
Source: IPM Images

Gaeumannomyces graminis (Sacc.) von Arx et D. Olivier - (take-all)

The fungus causes a serious, soil-borne disease of cereals and grasses which is wide-spread in temperate regions. The disease is particularly destructive in wheat and barley where losses of up to 70% can occur. The fungus invades the roots and lower stems which turn black and die off. The diseased plants can be pulled out easily. Above-ground symptoms include yellowing, stunting and poorly developed heads ("whiteheads").

Since the fungus spreads through the soil the disease is usually distributed in patches. Inoculum sources are plant residues from the previous year or alternate grass hosts like weeds. It can also survive saprophytically for 1-2 years in plant debris. Chemical control and resistant varieties have shown only limited success. Crop rotation is usually recommended to reduce the soil inoculum, but cases of suppressive soils have been also reported.

Vernacular names
• Deutsch: Schwarzbeinigkeit
• English: take-all
• Español: mal de pie de los cereales
• Français: piétin échaudage

Perithecia (ascoma) are black and 300-500 µm large. Mature ascospores are yellowish with 3-7 septa and around 70-100 µm long. Conidia are 4-7 x 1-1.5 µm large. Some strain form microsclerotia (about 1mm large) as well as chlamydospores.

Varieties of the fungus:
Gaeumannomyces graminis var. avenae (E.M. Turner) Dennis - attacks oats and turfgrasses
Gaeumannomyces graminis var. graminis (Sacc.) v. Arx and Olivier - infects turfgrasses and rice
Gaeumannomyces graminis var. tritici J. Walker - infects wheat and barley

Ophiobolus graminis