Exploiting sources of resistance to Turnip yellows virus for deployment in oilseed rape.

- The virus, Turnip yellows virus is found every year infecting most oilseed rape crops in the UK. In some crops, every single plant is infected. The virus has been shown to reduce the seed yield of oilseed rape crops in the UK by up to 30%. - The virus is spread by greenfly and growers use insecticides to try to stop the greenfly spreading the virus to oilseed rape crops; the insecticides are not always particularly effective at stopping spread of the virus. - We have identified a number of different plant lines with natural resistance to Turnip yellows virus. - The different resistance sources we have identified will be evaluated against genetically different Turnip yellows virus isolates. - The purpose of our research is to produce tools (markers) that will allow plant breeding companies to incorporate the natural virus resistance we have found in to their commercial oilseed rape varieties. - Once the seed and markers have been handed over to seed companies, we will support them in incorporating / breeding the resistance in to their commercial oilseed rape varieties. - The ultimate aim is to provide farmers with virus resistant oilseed rape varieties that will not become infected by the virus, or will tolerate some virus infection with minimal loss of yield. - This will increase production whilst at the same time reducing inputs and energy costs / consumption. It will also reduce the farmers' dependence on insecticides and provide an environmentally friendly, sustainable means of increasing oilseed rape yields.

The virus, Turnip yellows virus (TuYV) is found every year infecting most oilseed rape (Brassica napus) crops in the UK. In some crops, there is 100% infection. The virus has been shown to reduce the seed yield of rape crops in the UK by up to 30% and our experiments on a current revealed a seed yield loss of 45%. TuYV is spread by aphids and growers use insecticidal treatments to try to stop aphid transmission to oilseed rape crops; the insecticides are not always particularly effective in stopping spread of the virus. We have identified an oilseed rape cultivar with quantitative resistance to TuYV (infected plants accumulated significantly less virus than 25 B. napus lines from the Warwick HRI Diversity Fixed Foundation Set ). The seed yield of infected plants was not significantly less than that of uninfected plants in this cultivar. We have also identified complete resistance (no virus infection detectable) to TuYV in some Brassica oleracea lines and Brassica rapa lines. The different resistance sources we have identified will be evaluated against genetically different Turnip yellows virus isolates from the UK. We will take a twin track approach and map the QTLs associated with the quantitative resistance in B. napus and also map the gene(s) controlling the extreme resistance in B. oleracea and B. rapa. Molecular markers for the resistances will be developed that will allow the quantitative resistance to be incorporated in to commercial rape varieties by conventional marker-assisted breeding and the extreme resistance to be incorporated via a resynthesised B. napus route. Once the seed and markers have been handed over to seed companies at the end of the project, we will continue to support them in incorporating the resistance(s) in to their commercial rape varieties. The ultimate aim is to provide farmers with virus resistant oilseed rape varieties in order to increase yields and reduce inputs .

The new plant genes providing natural resistance to an important virus with allele-specific markers for crop improvement will benefit the breeding companies initially. High levels of TuYV infection of oilseed rape have been seen in recent years. Estimates of yield losses due to TuYV in the UK range from 9-30%. Experiments we have carried out on a current cultivar indicate the losses could be much greater than this (45%) in years of high infection. Consequently, virus-resistant oilseed rape lines will have an advantage in the market place, provided they are otherwise competitive. The use of marker-assisted selection to introgress the virus resistances in to current oilseed rape varieties should minimise linkage drag. The delivery of three different natural sources of resistance to breeders will provide options for combining the genes (pyramiding) or deploying separately and prolonging the useful life of the resistances in the field. The farmers will also be major beneficiaries as they will be able to reduce crop losses in an environmentally and economically sustainable way. Resistance to the major virus in oilseed rape (TuYV) will remove the dependence on and need for insecticidal treatments aimed at controlling the virus (the aphids that transmit the virus are not a major problem in oilseed rape in their own right; growers use the autumn insecticidal treatments primarily in the hope of controlling the virus). This will have environmental as well as economic benefits. The reduction in pesticide usage will also reduce the selection pressure for aphid biotypes with insecticide resistance. The general public will benefit from the research in that it will contribute to food security by providing control measures for a widespread and important crop virus, where currently there appear to be no viable control measures. The academic beneficiaries are listed in the 'Academic Beneficiaries' section.