Molecular aspects
of endophyte and parasite infections of crop plants
C. Jansen (1), D. von Wettstein (2), W. Schäfer (3), K.-H. Kogel (1), A. Felk (3), F. J. Maier (3)
(1) Institute of Phytopathology and Applied
Zoology, Justus-Liebig-University Giessen, Heinrich-Buff-Ring 26-32, D-35392
Giessen, ALLEMAGNE
(2) Department of Crop and Soil Sciences,
School of Molecular Biosciences and Center for Integrated Biotechnology,
Washingston State University, Pullman, WA 99164-6420; USA
(3) Department of Molecular Phytopathology and
Genetics, University of Hamburg, Biocenter Klein Flottbek, Ohnhorststrasse 18,
D-22609 Hamburg, ALLEMAGNE
Fusarium head
blight epidemics of wheat and barley cause heavy economic losses to farmers due
to yield decreases and production of mycotoxin that renders the grain useless
for flour and malt products. No highly resistant cultivars are available at
present. Hyphae of germinating fungal spores use different paths of infection:
After germination at the extruded tip of an ovary, the hyphae travel along the
epicarp in the space between the lemma and palea. Infection of the developing
kernel proceeds through the epicarp, successively destroying the layers of the
fruit coat and finally the starch and protein accumulating endosperm. Hyphae
reaching the rachis proceed to apically located developing kernels. Using a
constitutively green fluorescence protein-expressing Fusarium wild-type
strain, and its knockout mutant, preventing trichothecene synthesis, we
demonstrate that trichothecenes are not a virulence factor during infection
through the fruit coat. In the absence of trichothecenes, the fungus is blocked
by the development of heavy cell wall thickenings in the rachis node of Nandu
wheat, a defense inhibited by the mycotoxin. In barley hyphae of both wild-type
and the trichothecene knockout mutant, are inhibited at the rachis node and
rachilla, limiting infection of adjacent florets through the phloem and along
the surface of the rachis. Effective resistance to Fusarium head blight
requires expression of genes that combat these different pathways of infection.