Molecular Plant Pathology - Pathogen Profiles
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Gaeumannomyces graminis, the take-all fungus and its
relatives
Jacqeline Freeman and Elaine Ward
Wheat Pathogenesis Programme, Plant-Pathogen Interactions
Division, Rothamsted Research, Harpenden, Herts. AL5 2JQ, UK
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| Summary: |
Take-all, caused by the fungus Gaeumannomyces
graminis var. tritici, is the most important root disease of
wheat worldwide. Many years of intensive research, reflected by the large
volume of literature on take-all, has led to a considerable degree of
understanding of many aspects of the disease. However, effective and
economic control of the disease remains difficult. The application of
molecular techniques to study G. graminis and related fungi
has resulted in some significant advances, particularly in the development
of improved methods for identification and in elucidating the role of the
enzyme avenacinase as a pathogenicity determinant in the closely related
oat take-all fungus (G. graminis var. avenae). Some
progress in identifying other factors that may be involved in determining
host range and pathogenicity has been made, despite the difficulties of
performing genetic analyses and the lack of a reliable transformation
system. |
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Infection of wheat by Gaeumannomyces
graminis and Phialophora graminicola. (a) G. graminis
var. tritici: perithecia produced on wheat roots in a rotting test,
surrounded by released asci; (b) G. graminis var. tritici:
ascospores in a single ascus (arrowed, a), with one ascospore separated
from the ascus (arrowed, as); (c) G. graminis var. tritici:
dark runner hyphae on the surface of a wheat root; (d) a patch of stunted
and yellowed wheat plants (foreground), typical of take-all, in the
summer; (e) whiteheads of infected plants in a wheat crop with take-all,
in late summer; (f) similarities in discoloration of wheat roots, and
differences in stem-base blackening of wheat, caused by infection with G. graminis
var. tritici (Ggt) (left), G. graminis var. graminis
(Ggg) (centre) and P. graminicola (right), in a pathogenicity
test; (g) Phialophora sp. (lobed-hyphopodia): lobed hyphopodia on
the leaf sheath at the stem base of a wheat plant; (h) Phialophora
sp. (lobed-hyphopodia): swollen cells with pores (known as growth
cessation structures or vesicles) in a wheat root; (i) P. graminicola:
swollen cells with pores (known as growth cessation structures or
vesicles) in a wheat root. Images (a), (b), (d), (f), (h) and (i) were
kindly provided by Richard Gutteridge (Rothamsted Research).
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