Differential interactions of <Emphasis Type="Italic">Verticillium longisporum</Emphasis> and <Emphasis Type="Italic">V. dahliae</Emphasis> with <Emphasis Type="Italic">Brassica napus</Emphasis> detected with molecular and histological techniques |
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| Authors: | C Eynck B Koopmann G Grunewaldt-Stoecker P Karlovsky A von Tiedemann |
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| Institution: | 1.Plant Pathology and Plant Protection Division, Department of Crop Sciences, Faculty of Agriculture,Georg-August University G?ttingen,Goettingen,Germany;2.Molecular Phytopathology and Mycotoxin Research Division, Department of Crop Sciences, Faculty of Agriculture,Georg-August University G?ttingen,Goettingen,Germany;3.Institute for Plant Diseases and Plant Protection,University of Hannover,Hannover,Germany |
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| Abstract: | The differential interactions of V. longisporum (VL) and V. dahliae (VD) on the root surface and in the root and shoot vascular system of Brassica napus were studied by confocal laser scanning microscopy (CLSM), using GFP tagging and conventional fluorescence dyes, acid fuchsin
and acridin orange. VL and VD transformants expressing sGFP were generated by Agrobacterium-mediated transformation. GFP signals were less homogenous and GFP tagging performed less satisfactory than the conventional
fluorescence staining when both were studied with CLSM. Interactions of both pathogens were largely restricted to the root
hair zone. At 24 h post-inoculation (hpi), hyphae of VL and VD were found intensely interwoven with the root hairs. Hyphae
of VL followed the root hairs towards the root surface. At 36 hpi, VL hyphae started to cover the roots with a hyphal net
strictly following the grooves of the junctions of the epidermal cells. VL started to penetrate the root epidermal cells without
any conspicuous infection structures. Subsequently, hyphae grew intracellularly and intercellularly through the root cortex
towards the central cylinder, without inducing any visible plant responses. Colonisation of the xylem vessels in the shoot
with VL was restricted to individual vessels entirely filled with mycelium and conidia, while adjacent vessels remained completely
unaffected. This may explain why no wilt symptoms occur in B. napus infected with VL. Elevated amounts of fungal DNA were detectable in the hypocotyls 14 days post-inoculation (dpi) and in
the leaves 35 dpi. Root penetration was also observed for VD, however, with no directed root surface growth and mainly an
intercellular invasion of the root tissue. In contrast to VL, VD started ample formation of conidia on the roots, and was
unable to spread systemically into the shoots. VD did not form microsclerotia in the root tissue as widely observed for VL.
This study confirms that VD is non-pathogenic on B. napus and demonstrates that non-host resistance against this fungus materializes in restriction of systemic spread rather than
inhibition of penetration. |
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| Keywords: | Oilseed rape GFP Confocal laser microscopy Agrobacterium-mediated transformation Non-host resistance Vascular diseases |
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