Gaeumannomyces graminis (Sacc.) Arx & D. Olivier var. tritici J. Walker
- Symptoms: A field infected by the fungus may have poorly defined patches where plants are stunted, have few tillers, and display drought symptoms. White heads are produced after flowering where plants produce no seed. Whole plants are affected, unlike crown rot where whiteheads affect single tillers, on plants (picture at left). The fungus causes rotting of the roots and lower stems. Basal stem and leaf sheath tissues, as well as roots, may turn a shiny black color (picture at right). When examined with a hand lens (10x1), dark fungal hyphae may often be found on the sub-crown internode between the old leaf sheaths. Coarse, black runner hyphae are conspicuous on the roots, and roots typically have black centers when broken and viewed end on.
- Development: The fungus persists on crop debris in the soil. Initial infections come from contact with hyphae or ascospores in the soil. Infection can occur throughout the crop cycle, but is favored by cool (12-18 degrees Celsius) soil temperatures and mildly alkaline or nutrient deficient soils, particularly coarse-textured, sandy soils. Nitrate also appears to enhance disease development. Infections of the roots in the fall and early spring generally progress to the crown and lower stem tissues; infections occurring later in the crop cycle cause less damage since they are usually confined to the roots.
- Hosts/Distribution: The take-all fungus displays a degree of specialization for wheat, triticale, and several related grasses. The disease is largely associated with temperate growing regions, but has been found in a wide range of environments, including tropical regions.
- Importance: Take-all is widespread in mono-cropped areas, especially where liming or minimum tillage is practiced. Losses to take-all can be severe, with large patches in fields having 100% grain yield loss.
Reference:
- Dr. Hugh Wallwork- Senior Plant Pathologist, South Australian Research Development Institute, Australia.