Abstract
Oilseed rape (OSR) is a major crop in the UK (620,000 Ha in 2008, 13.1% of cropped land; Defra Statistics). It is subject to a number of well established diseases but this project addresses the potential of a disease new to the UK to damage production. Verticillium longisporum has had a major impact on OSR in northern Europe but is newly reported in the UK. The most important symptom is early ripening leading to loss of yield; this is exacerbated by dry weather. Other plant pathogenic Verticillium species are well established in the UK but these do not affect OSR. V. longisporum is effectively a pathogen only of crucifers. In OSR it has, until now, been confined to Europe. It does occur in other crops such as cauliflowers and horseradish, and in these is known in Europe, in Asia and in the USA. It is highly unusual genetically and appears to be a hybrid between the widespread and common V. dahliae and an as yet unidentified second species. The disease is soil-borne and can persist for many years in infested fields. Control is known is to be difficult as no fungicides are effective on infected plants. Generally the most effective means of managing verticillium wilt diseases has been through soil-sterilisation but this is not usually cost effective for broad-acre crops like OSR. At present there are no environmentally sustainable approaches to managing infested fields other than instigating very long rotations. (In Sweden, 10-15 years between susceptible crops has been recommended in some circumstances.) In the UK V. longisporum has only been reported from OSR to date. However, there are no discernable differences between most European isolates from OSR and those from vegetable Brassica crops and spread to the latter must be a possibility. Whilst we can gather some information from existing research, much remains unknown about the current situation and potentially how serious the disease will be under our conditions. This project sets out to provide tools for efficiently studying the disease and to start laying the ground for sustainable control through four objectives 1. To molecularly characterise UK isolates of V. longisporum. This will allows us to develop diagnostic procedures safe in the knowledge they are effective and appropriate for use in the UK. It will also tell us whether infection has been introduced from Europe or whether these particular hybrid isolates arose in the UK. 2. To develop fast, effective and specific procedures for detecting and identifying OSR-infecting isolates in soil and in planta. Identification of infection can be difficult – symptoms may be masked by other diseases or be rather indeterminate. Being able to rapidly quantitate the fungus in the soil will enable us to study risk factors and predict disease levels. Moreover, rapid and cost effective diagnostics will potentially allow soil-testing services which will allow growers to identify and avoid infested fields to be set up. 3. To undertake preliminary field studies. We need to study many aspects of the disease and its behaviour under UK conditions; how widespread is it; how long does it last in the soil; how serious is yield loss in our wetter climate? 4. To screen parents and progeny from mapped populations for sources of resistance. In the long term the most sustainable control is likely to be through the use of resistant varieties. No such varieties exist at present and this objective will look for sources of resistance that can be used in breeding programmes. Verticillium wilt in OSR has obvious potential to be damaging to individual farmers, but it is also possibly a cause of wider concern as growers seek to maintain yields by extending areas of monoculture and potentially by applying unsustainable approaches to control. This project aims to provide the tools to study the disease and to begin to begin broadening our knowledge of the situation in the UK, with the long-term intention of providing sustainable approaches to disease management.
United Kingdom