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Factors Affecting the Inoculum potential of soilborne plant pathogens - HH3230SFV

Soilborne pathogens remain among the most intractable problems for horticulture. Chemical control methods are often limited and where they do exist, rely on prophylactic treatments. Similarly, resistant varieties are often not available or are ineffective. Consequently, a clear understanding of the biology of such pathogens is imperative to plan appropriate disease control or avoidance procedures and to target available chemicals optimally, thus reducing chemical inputs into the environment.

Three economically important soilborne pathogens have proven particularly difficult to control in the UK. The first, Pythium violae causing carrot cavity spot, is considered the major disease problem on this crop, as effectively, any lesion on the root makes sale impossible. In bad years, losses have been estimated at £20-30M per annum in the UK based on marketed value (Defra Horticultural Statistics). The second, Sclerotium cepivorum responsible for white rot of Allium species, is the major soilborne pathogen of onions and their allies with estimated annual losses due to this disease of £5M. The third, Sclerotinia sclerotiorum is a pathogen of numerous horticultural crops and in field lettuce alone losses of £10M per annum due to this pathogen have been estimated. Significantly, the continued presence of these pathogens in soil has resulted in some fields being taken out of production which constrains future cropping patterns.

A key gap in the knowledge of the biology of each of these pathogens concerns inoculum potential. Without an understanding of how much pathogen is present and the ability of this inoculum to cause infection, successful strategies for their control cannot be planned. Consequently, the major aim of this project is to examine the factors affecting inoculum potential of P. violae, S. cepivorum and S. sclerotiorum. Quantitative PCR procedures will be developed and used to monitor levels of P. violae both temporally and spatially under a range of environmental conditions in the field. Initially, for both S. cepivorum and S. sclerotiorum, the environmental factors (temperature and water availability) that break dormancy or condition sclerotia (overwintering resting bodies) so that they are capable of germination will be studied. Subsequently, the germination response to environmental treatments of sclerotia conditioned to varying extents will also be investigated. This information will be useful in predicting the likely problems associated with the presence of each of these pathogens in the soil and aid in developing strategies for disease control and more timely application of control measures for use by the industry.

Overall this work relates to Defra’s remit of developing a sustainable, diverse and dynamic farming industry and a competitive, safe and integrated food supply chain which is responsive to the needs of consumers. This will be achieved by optimising inputs and minimising pesticide usage which is considered environmentally desirable and would also conform to consumer demand for reduced pesticide levels in food. It will also lead to more sustainable production. Thus, it addresses the policy objective of ROAME A HH32 to provide robust strategies and methods of disease control suitable for integrated crop and farm management in line with the Government’s policy for pesticide minimisation.
Cavity spot of carrot - Pythium violae

1. To complete development and validation of a PCR based test for the quantitation of P. violae in soil from an infested field.
2. To determine the dynamics of P. violae in a field soil over four years and to correlate this with environmental factors (soil temperature; soil moisture; crop grown) and, where carrots are grown, with cavity spot disease incidence.
3. To test samples from commercial growers for the presence of P. violae and P. sulcatum and to correlate these with the grower’s reports on the severity of the disease outbreak.

Allium white rot - Sclerotium cepivorum

4. To develop a garlic extract (DADS) assay to test the germination response of conditioned sclerotia of S. cepivorum.
5. To determine the effect of soil temperature and water potential on the conditioning and survival of S. cepivorum sclerotia.

Sclerotinia disease - Sclerotinia sclerotiorum

6. To collect and characterise 50 UK isolates of S. sclerotiorum using DNA fingerprinting and mycelial compatibility tests.
7. To determine the initial response of sclerotia from at least five dominant S. sclerotiorum clones to environmental conditioning and the subsequent effect of temperature and water potential on germination.
Project Documents
• Final Report : Factors affecting the inoculum potential of soilborne plant pathogens   (464k)
Time-Scale and Cost
From: 2005

To: 2009

Cost: £1,056,366
Contractor / Funded Organisations
Warwick - HRI
Allocated - WHRI              
Sustainable Farming and Food              
Sustainable Production              
Fields of Study