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Understanding Sclerotinia infection in oilseed rape to improve risk assessment and disease escape - LK0957

Description
Background and purpose: Sclerotinia in oilseed rape is a sporadic disease, but occasional severe outbreaks occur. If these are not controlled, fungal resting bodies are left in the soil, which increase the risk of disease for several years. Hence, approximately one third of oilseed rape (OSR) crops are sprayed for Sclerotinia – the majority unnecessarily. Resistance to MBC fungicides is now widespread in France and is likely to occur in the UK. Fungicide dependence could be reduced by: (i) improved forecasting of the disease risk, and (ii) the development of varieties with ‘field resistance’. Both would be advanced by improved understanding of the dynamics of the infection process. Infection is known to occur via ascospore infected petals, but there is unexplained variation in the relationship between petal infection and subsequent development of disease. The importance of primary infection via tissues other than petals is not currently known. These early phases of the epidemiology will be quantified utilising near isogenic lines (NILs) of OSR, developed by CPB-Twyford, that differ only for the presence or absence of petals. These will allow mechanisms for this variation to be tested and, additionally, the disease escape benefits from apetalous varieties to be assessed. Previous ‘apetalous’ winter oilseed rape lines have not been sufficiently apetalous or genetically stable to allow this.

Objectives: (1) Determine the distribution of S. sclerotiorum ascospore inoculum on plants within experimental plots of winter OSR. (2) Quantify the relative importance of petals and other floral parts, including pollen, in the Sclerotinia stem rot infection process. (3) Compare disease incidence in apetalous and full-petal NILs of oilseed rape under conditions of similar inoculum pressure. (4) Assess the potential of PCR-based inoculum detection as an aid to risk assessment by correlating inoculum density determined by such assays with realised stem rots. (5) Test the infection model using an array of recombinant doubled haploid lines segregating for the apetalous/fully petal trait.

Benefits to industry, science and the environment: (1) The PCR method for detection of S. sclerotiorum will be evaluated as a potential tool to use in a risk assessment protocol. (2) A quantified estimate will be made of the importance of primary inoculum, petals and other tissues in the initial infection process. (3) An improved understanding of the importance of different infection routes for S. sclerotiorum will have a wider relevance to infection of other crops by this pathogen. (4) An improved understanding of the S. sclerotiorum infection process could help to develop a forecasting protocol, which would lead to reduced fungicide use on existing oilseed crops, with potential cost savings and an increase in gross margins. (5) The potential for avoidance of S. sclerotiorum infections by apetalous OSR will be evaluated.

Programme of work: In year 1 and 2, NILs of apetalous and full petal OSR will be established at ADAS Rosemaund (field site) and CPB Twyford (polytunnels and a naturally infected field site), and in year 3, new recombinant lines of apetalous and full petal OSR will be established at Rosemaund and CPB Twyford. All plots will be inoculated with Sclerotinia (sclerotia and ascospores). The presence of Sclerotinia on petals, stamens and sepals will be quantified during flowering, by agar plating, and by PCR testing at Rothamsted Research. The time course of Sclerotinia growth along the petiole to the main stem will be determined. Airborne inoculum will be monitored by continuous spore trapping. Stem rot and yields of the NILs will be compared, and related to measurements of spores in the air and on flower parts.

Exploitation: The increased understanding of the infection process for Sclerotinia will enable improved guidance on Sclerotinia control to be given, which could be delivered by DSS such as the PASSWORD system. The PCR assay may lead to a commercial petal test for farmers as part of their decision making process. This may be extended to regional risk assessment for Sclerotinia infection. CPB Twyford is developing apetalous material based on the physiological advantages. Improved knowledge of the basis of Sclerotinia avoidance will be used to aid the breeding efforts of CPB Twyford and other breeding companies.

Objective
11 Objective(s)

11.1 Scientific objective(s)
Objective 1: Determine the distribution of S. sclerotiorum ascospore inoculum on plants within experimental plots of winter oilseed rape.

Objective 2: Quantify the relative importance of petals and other floral parts, including pollen, in the Sclerotinia stem rot infection process.

Objective 3: Compare disease incidence in apetalous and full-petal NILs of oilseed rape under conditions of similar inoculum pressure.

Objective 4: Assess the potential of PCR-based inoculum detection as an aid to risk assessment by correlating inoculum density determined by such assays with realised stem rots.

Objective 5: Test the infection model using an array of recombinant doubled haploid lines segregating for the apetalous/fully petal trait.
11.2 Interdependence of objectives
Objective 1 (determining distribution of Sclerotinia) is not dependent on objectives 2 or 3, but is partly dependent on objective 4 (development of PCR). Objective 2 (quantifying relative importance of flower parts in infection) depends on objectives 3 (a significant level of Sclerotinia stem rot) and 4. Objective 3 is not dependent on the other objectives. Objective 5 is partly dependent on all other objectives.
11.3 Chances of achieving objectives
There is a high probability of achieving the objectives. The participants have a proven record of work with oilseed rape establishment and monitoring, and with production of Sclerotinia inoculum and detection of Sclerotinia in plants. Sclerotinia development in field plots is dependent on weather factors and spring inoculum levels, but the chances of disease will be maximised by introducing inoculum, and irrigating the crop if necessary during flowering to create a wet canopy. Oilseed rape grown in CPB Twyford polytunnels which have been cropped continuously with oilseed rape and are known to be infested with Sclerotinia, will provide an additional source of diseased plants for sampling and detection. Previous work has shown that PCR-based assays can detect S. sclerotiorum inoculum in spore trap samples and on oilseed rape petals.
11.4 Factors, specific to the project, which might delay achieving the objective(s)

If establishment of the field crops is less than satisfactory in any year, this would mean loss of data for that year and crop. All measures will be taken to achieve the best establishment possible. Plots for the 2004 harvest year have already been established successfully. If inoculum of S. sclerotiorum is low in any one field year, and environmental conditions are unsuitable for infection during flowering, this will result in low stem rot and thus difficulties in interpreting data on infection from various flower parts. Introduction of S. sclerotiorum inoculum, and irrigation during flowering, should maximise stem rot development. If necessary, progress on determining the relative importance of the different routes of infection could be achieved through artificial inoculation experiments in the polytunnel at CPB Twyford and in controlled environments at Rothamsted Research.
Time-Scale and Cost
From: 2004

To: 2007

Cost: £118,007
Contractor / Funded Organisations
Rothamsted Research (BBSRC), CPB Twyford Ltd, Home Grown Cereals Authority, ADAS UK Ltd.
Keywords
Arable Farming              
Crop Diseases              
Crops              
Farming              
LINK Programme              
Sustainable Farming and Food              
Sustainable Production              
Fields of Study
Arable Crops