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Epidemiology of downy mildew on HNS. - HH1749SHN


Downy mildew, caused by Peronospora sparsa, is a serious disease on roses. The biology and epidemiology of this disease are poorly understood and this hinders the development of a more rational disease management strategy. A three-year research project on the biology and epidemiology of rose downy mildew is proposed. Overwintering pathogen structures will be observed. Techniques will be developed to maintain and bulk up the fungus on detached leaves and/or micro-propagated plants in vitro, a fundamental requirement for research on quantitative epidemiology and molecular pathogen detection. Histological work will be done to determine the infection and colonisation processes and thus to determine whether and to what extent the fungus is able to invade the vascular tissues, leading to the establishment of systemic infections. Efficient methods will be developed to assess the host resistance/susceptibility to this fungus. The effects of environmental conditions on infection and sporulation will be determined and mathematical models will be developed to describe such effects.

The research work will provide essential knowledge for developing sustainable management of rose downy mildew. It will also provide essential techniques for future studies of host-pathogen genetics and for breeding cultivars with durable resistance. These techniques will also enable similar work on downy mildews of other HONS or ornamental crops to be carried out. This would assist growers in increasing the quantity and quality of rose production whilst minimising the use of fungicides to satisfy public demand.

The overall objectives are:
to determine the overwintering stage(s) of the fungus;
to establish efficient techniques for maintaining and producing spore/mycelium in vitro;
to develop histological techniques for observing infection structures and colonising host tissues;
to conduct preliminary work to develop molecular methods for detecting the fungus in the host;
to design an optimum scheme for sampling diseases incorporating the effects of wind direction and speed on pathogen dispersal using a stochastic model.

The specific objective to achieve these are:
1. To observe and determine the overwintering structures and initial spring epidemic development in field conditions.
2. To establish techniques for micro-propagation of rose cultivars susceptible to the fungus.
3. To develop an efficient protocol for inoculating micropropagated plants for subsequent histological, epidemiological and molecular studies.
4. To develop an efficient and consistent method for producing and storing spores on micropropagated plants.
5. To conduct initial histological studies to determine the processes of infection, colonisation and sporulation on host tissues including leaves and buds.
6. To conduct preliminary experiments to determine the possibility of the fungus invading vascular tissues and thus establishing the probability of systemic infection.
7. To complete the literature search on PCR primer(s) for downy midlew in general with a view to developing primers specific to P. sparsa.
8. To design an optimum scheme for sampling diseases incorporating the effects of wind direction and speed on pathogen dispersal using a stochastic simulation model.
Project Documents
• Final Report : Epidemiology of downy mildew on HNS.   (4119k)
Time-Scale and Cost
From: 1999

To: 2002

Cost: £253,050
Contractor / Funded Organisations
Horticulture Research International
Crop Diseases              
Hardy Nursery Stock              
Fields of Study