The situation
Crook root disease of watercress (Rorippa nasturtium-aquaticum) caused by Spongospora subterranea f. sp. nasturtii is a serious problem for English watercress growers particularly during the colder months of the year (October to May). The pathogen has the aditional importance of acting as the vector of watercress yellow spot virus (WYSV) which can also cause major problems during winter and spring.
The producers apply routinely zinc to the supplied water to control the pathogen. But there are increasing concerns about envorinmental pollution.
Research
Research on both the vector (biology, control) and the virus has beeng carried out at HRI (see below).
Future rearch concentrates on the possibility of resistance breeding.
In collaboration with Dr Ueli Merz of ETH Zurich, the crook root agent with its supposed close relative Spongospora subterranea f.sp. subterranea (Sss) the agent of powdery scab of potato has been compared. Ssn is unusual in that it is the only plasmodiophoromycete known to transmit an isometric plant virus. Sss transmits the filamentous virus, potato mop-top virus. In collaboration with Dr Merz a polyclonal antiserum to the spore ball stage of Sss was produced. This was shown to give sensitive detection of spore balls in vitro and quantitative detection in soil, particularly when soils contained 2000 spore balls per g. soil. (Swiss National Science Foundation/British Council funded). Further a monoclonal antibody to spore balls was produced. Sporosori of both Spongospora showed the same reaction in ELISA.
John Walshs group has stopped the research on Ssn and works now on Turnip Mosaic Virus TuMV.
PUBLICATIONS
WALSH, J.A., CLAY, C.M., MILLER, A. & ROWE, J.C. (1989). A fungus-transmitted virus of watercress. Aspects of Applied Biology 22, 101-108.
CLAY, C.M. & WALSH, J.A. (1989). The ultrastructure of Spongospora subterranea f.sp. nasturtii. Aspects of Applied Biology 22, 415-417.
WALSH, J.A., CLAY, C.M. & MILLER, A. (1989). A new virus disease of watercress inEngland. OEPP/EPPO Bulletin 19, 463-470.
CLAY, C.M. & WALSH, J.A. (1989). The ultrastructure of Spongospora subterranea f. sp. nasturtii. In Electron Microscopy Applied in Plant Pathology Konstanz, p. 31.
CLAY, C.M. & WALSH, J.A. (1990). Ultrastructure of sporangial development in Spongospora subterranea f. sp. nasturtii infecting watercress. Mycological Research 94(4) 463-471.
WALSH,J.A. (1990). The epidemiology of watercress yellow spot virus. In: Proceedings of the First Symposium of the International Working Group on Plant Viruses with Fungal Vectors, Braunschweig, Germany, August 1990, (ed. R. Koenig), Schriftenreihe der Deutschen Phytomedizinischen Gesellschaft, Stuttgart, Ulmer, pp.173-176.
WALSH, J.A. & PHELPS, K. (1991). Development and evaluation of a technique for screening watercress (Rorippa nasturtium-aquaticum) for resistance to watercress yellow spot virus and crook root fungus (Spongospora subterranea f. sp. nasturtii). Plant Pathology 40, 212-220.
WALSH, J.A. (1992). The epidemiology and control of watercress yellow spot virus. 7th Conference ISHS Vegetable Virus Working Group. Recent Advances in Vegetable Virus Research, Athens, Greece, July 12-16, 1992. 2pp.
WALSH, J.A. (1992). Resistant Watercress. Grower, 118 (6), 18-21.
WALSH, J.A. & CLAY, C.M. (1993). A summary of research on watercress yellow spot virus and its fungal vector Spongospora subterranea f.sp. nasturtii. Proceedings of the Second Symposium of the International Working Group on Plant Viruses with Fungal Vectors, Montreal, Canada, 25th - 27th July 1993, pp 111-114.
WALSH, J.A. & CLAY, C.M. (1993). The characterisation, epidemiology and control of watercress yellow spot virus and its fungal vector Spongospora subterranea f. sp. nasturtii. Proceedings of the 6th International Congress of Plant Pathology held in Montreal, Canada, 28 July - 6 August 1993, p 305.
WALSH, J.A. (in press). Chemical control of fungal vectors of plant viruses. In: Plant Virus Disease Control. APS Press, St Paul, MN, USA.
CLAY, C.M. & WALSH, J.A. (1995). Cytopathic alterations in watercress leaf tissue infected with watercress yellow spot virus. Proceedings of the 8th International Conference on Virus Diseases of Vegetables, Prague, Czech Republic, 9-15 July 1995, ISHS Vegetable Virus Working Group, 133-135.
MERZ, U. & WALSH, J.A. (1995). The potential of serology for the detection of Spongospora subterranea f. sp. subterranea. Autumn meeting of the Swiss Society for Phytomedicine, ETH Zurich, October 5th. 1995.
CLAY, C.M. & WALSH, J.A. (submitted 30.1.96). Spongospora subterranea f. sp. nasturtii, ultrastructure of the plasmodial-host interface, food vacuoles, flagellar apparatus and exit pores. Mycological Research.
WALSH, J.A. & MERZ, U. (1996). Serological detection of Spongospora subterranea f. sp. subterranea. Proceedings of the 1996 BCPC Symposium, Diagnostics in Crop Production, University of Warwick, 1-3 April 1996, 151-156.
MERZ, U., WALSH, J.A. & HARRISON, J.G. (1996). The potential of serology for the detection of Spongospora subterranea in soil. Proceedings of the 1996 BCPC Symposium, Diagnostics in Crop Production, University of Warwick, 1-3 April 1996, 269-274.
WALSH, J.A., MERZ, U. & HARRISON, J.G. (1996). Serological detection of spore balls of Spongospora subterranea and quantification in soil. Plant Pathology 45 (5), 884-895.
Contact address:
Dr. John A. Walsh Plant-Virus Interactions Group Warwick HRI Warwick University Wellesbourne Warwick CV35 9EF UK Phone: 44-1789-470 382 Fax: 44-1789-470 552
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