Department of Crop Sciences - Division of Plant Pathology and Crop Protection

General Plant Pathology and Crop Protection

Prof. Andreas von Tiedemann

arrow Dept. Crop Sciences arrow Div. Plant Pathology and Crop Protection  arrow Research Sect. General Plant Pathology  arrow Verticillium longisporum

Verticillium longisporum on oilseed rape

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Verticillium longisporum (VL) is a host-adapted, near-diploid, vascular fungal pathogen of oilseed rape (Brassica napus L. spp. oleifera) (Zeise & Tiedemann, 2001, 2002). The growing area of intense rapeseed cultivation has rendered this disease an increasing threat to oilseed rape (OSR) production particularly in Europe. Unlike other Verticillium diseases VL does not induce wilting, but premature senescence and ripening which may severely reduce yields (Fig. 1.). Fig.2.: Verticillium stunting of oilseed rape Fig.2.: Microsclerotia of Verticillium longisporum on oilseed rape stemsFig.3.: Verticillium stunting of oilseed rapeArtificially inoculated plants in the greenhouse show a distinct stunting of the shoots (Fig. 2.) . As fungicides for direct control of the disease are unavailable, crop protection relies on the resistance of cultivars. Recently, we identified some promising genotypes of cabbage (B. oleracea) with enhanced resistance (Rygulla et al. 2007a). Using such resistant genotypes of B. oleracea as parental lines OSR lines with high resistance against VL were resynthesized (Rygulla et al. 2007b).
A closely related species to V. longisporum is V. dahliae (VD). This ubiquitous soilborne fungus causes wilt diseases on many economically important crops, including cotton, cucurbits, alfalfa, sunflower, eggplant, mint, strawberry, tomato and potato. A differentiation of long-spored Verticillium isolates collected from horseradish, classified as Verticillium dahliae var. longisporum, was first made in the early 1960s, until the detailed description of distinct morphological, physiological and molecular traits led to the proposition of treating V. longisporum as a distinct species. Nonetheless, there is still controversy concerning the taxonomy of V. longisporum as a separate host-specific species of Verticillium. Thus it has been reported that Brassica crops can occasionally host short-spored Verticillium isolates and that V. longisporum is able to infect plant species outside the Brassicaceae family. Additional confusion has been caused by some misidentification of the two species. In several studies, V. dahliae has been regarded to be the causal agent of Verticillium wilt in Brassica crops or on horseradish, without considering that long-spored isolates may have been involved.
In earlier studies we investigated the host specificity of VL vs. VD and found a clear restriction of VD to non-Brassica hosts while VL was pathogenic only on Brassica species. Thus, both species possess non-overlapping host range (Zeise u. Tiedemann, 2001, 2002a & b). We also investigated the differential interactions of VL and VD on the root surface and in the root and shoot vascular system of Brassica napus L. by confocal laser scanning microscopy (CLSM), using GFP tagging and conventional fluorescence dyes, acid fuchsin and acridin orange (Eynck et al. 2007). Fig.4.: mycelium of Verticillium longisporum on the root surface of oilseed rapeVerticillium longisporum growing in vessels of oilseed rape VL and VD transformants expressing sGFP were generated by Agrobacterium-mediated transformation. Interactions of both pathogens were largely restricted to the root hair zone. At 24 hours 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.
An additional phenomenon investigated is the stunting of plants infected by VL in controlled environments. As wilting toxins are not present and water relations are unaffected we assume a distinct modulation of plant growth by chemical signals deriving from the fungus. As stunting of shoots becomes effective distinctly before the fungus invades the shoot vascular system a systemic signal secreted by the pathogen during colonization of the roots may be responsible for the disease phenotype. In our studies with susceptible rapid-cycling B. napus plants we did not detect any host responses typically found during penetration and establishment of fungal pathogens such as an oxidative burst or elevated levels of NO. Recently, a fungal metabolite secreted by VL was discovered which induces stunting. This compound is currently isolated in order to identify its chemical nature and to elucidate its biological function in the Verticillium-rapeseed interaction. This research is conducted in the framework of a DFG-funded research group.

Investigators: Dr. Karin Zeise, Christina Eynck (PhD), Nadine Riediger (PhD), Ruben Gödecke (Msc)
Supervisor: Prof. Andreas von Tiedemann

Selected publications:

Eynck, C., B. Koopmann, G. Grunewaldt-Stoecker, P. Karlovsky, A. v. Tiedemann (2007). Differential interactions of Verticillium longisporum and V. dahliae with Brassica napus detected with molecular and histological techniques. European Journal of Plant Pathology, 118:259-272.

Rygulla W, F. Seyis, C. Eynck, A. v. Tiedemann, W. Friedt, W. Lühs, RJ Snowdon (2007).  Combination of resistance to Verticillium longisporum from zero erucic acid Brassica oleracea and oilseed Brassica rapa genotypes in resynthesized rapeseed (Brassica napus) lines. Plant Breeding 126 (6), 596-602.

Rygulla W, RJ. Snowdon, C. Eynck, B. Koopmann, A. v. Tiedemann, W. Lühs, W. Friedt (2007).  Broadening the genetic basis of Verticillium longisporum resistance in Brassica napus by interspecific hybridisation. Phytopathology 97: 1391-1396.

Zeise, K. & A.v. Tiedemann (2001). Morphological and physiological differentiation among vegetative compatibility groups of Verticillium dahliae and V. longisporum. J. Phytopathology, 149, 469-475.

Zeise, K. & A.v. Tiedemann (2002a). Host specialization among vegetative compatibility groups of Verticillium dahliae in relation to V. longisporum. J. Phytopathology, 150, 112-119.

Zeise, K. & A.v. Tiedemann (2002b). Application of RAPD-PCR for analysis of virulence types within soil populations of Verticillium dahliae and V. longisporum. J. Phytopathology, 150, 557-563.