Infection of barley roots by Chaetomium globosum: evidence for a protective role of the exodermis.
Plant pathogenesis by fungi is known to be dependent on the host genotype, the virulence of the pathogen and certain environmental conditions influencing fungal establishment. Previously, it has been shown that Chaetomium globosum, a fungus well-characterized for its biocontrol potential, causes necrosis on barley roots grown in Murashige and Skoog (MS)-agar. Using MS-agar and aeroponic culture as axenic plant growth systems, C. globosum pathogenesis was analyzed with serological and histological methods. Irrespective of the growth system, C. globosum infected the root epidermis. Roots grown in MS-agar were extensively colonized intercellularly and intracellularly up to the inner cortex and the tissue underwent necrosis. In contrast, roots grown in aeroponic culture were not colonized beyond the epidermis and the roots appeared healthy. Histochemical analyses revealed that hypodermal suberization stopped fungal invasion. In root tips known to lack suberization, epidermal papilla formation reduced overall infection frequency. The results indicate that specific environmental conditions are important for infection and disease expression in barley roots. Infection is restricted by two spatial and temporal distinct defence mechanisms: (1) papillae in root tips retarding fungal invasion; and (2) suberization of hypodermal cells blocking fungal radial growth.
Reissinger
Annette
A
Soil Ecosystem Phytopathology, Institute for Plant Diseases, University of Bonn, Nussallee 9, 53115 Bonn, Germany. a.reissinger@uni-bonn.de
Winter
Stephan
S
Steckelbroeck
Stephan
S
Hartung
Wolfram
W
Sikora
Richard A
RA
D000818:Animals; D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal; D002597:Chaetomium / Q000254:growth & development / Q000276:immunology / Q000472:pathogenicity*; D001467:Hordeum / Q000382:microbiology*; D006825:Hybridomas; D051379:Mice; D010935:Plant Diseases / Q000382:microbiology*; D018517:Plant Roots / Q000382:microbiology
D000908:Antibodies, Fungal; D000911:Antibodies, Monoclonal