Exploiting new sources of broad-spectrum resistance to Turnip mosaic virus in brassicas (ExBSR)

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Turnip mosaic virus (TuMV) is an important pathogen that infects many crops worldwide (rated 2nd most important virus infecting field vegetables worldwide). It is most damaging in brassicas (cabbage, cauliflower, oilseed rape etc.) and spread by >89 different aphid species. It's very broad host range and the inability of pesticides to control it, emphasise the need for the development of plants with natural resistance to the virus.Many different strains of TuMV exist and resistances to restricted ranges of strains have been described. We have identified Brassica rapa (the most important vegetable brassica worldwide) lines with natural resistance to a broad range of TuMV strains. We have been unable to find any TuMV strains able to overcome these resistances, indicating they may be durable. Having identified the genes responsible for one of the sources of resistance and their mechanism, we developed a simple test to identify lines possessing different sources of broad-spectrum resistance. By deploying additional/new sources of resistance to TuMV, this will reduce the selection pressure for resistance-breaking strains of the virus. This project aims to exploit the best of these new sources of broad-spectrum resistance to TuMV. It will be necessary to breed the resistance into commercial plant varieties. This will be achieved in a collaborative venture between the University of Warwick (UoW), the student and the seed company, Sakata UK Ltd. To significantly speed up this process, the student will develop molecular markers for the plant genes responsible for TuMV resistance. The student and Sakata will use these markers in a process known as marker-assisted selection to get the resistance genes into plant varieties that have all the other plant traits needed for commercial production.The student will be trained at UoW in a range of scientific skills related to plant pathology and molecular biology with generic applicability and in plant breeding during a 3 month placement at Sakata. There is a lack of students being trained in plant pathology and horticulture; this student will help to address these skills gaps. The student will learn to handle and transmit plant viruses whilst testing the new sources of TuMV resistance against a broad range of TuMV isolates from Sakata and from the large Warwick TuMV diversity collection. The B. rapa line showing the most extreme resistance to the broadest range of TuMV isolates will be taken forward.The student will then cross the best virus-resistant plant line to a rapid-cycling plant line and commercial plant lines. The offspring will be tested for resistance / susceptibility to TuMV with careful visual observation and ELISA testing of plants for TuMV infection. If the offspring from the rapid-cycling cross are resistant, they will be backcrossed to the susceptible rapid-cycling parent and if they are susceptible, they will be backcrossed to the resistant parent. This will be done to develop a large plant population for mapping. The offspring of the cross with the commercial plant lines will be back-crossed with the commercial parents to commence introgression of the resistance in to commercially acceptable plant lines.The large plant population will be challenged with TuMV. Genotyping combined with the phenotyping will allow the resistance gene(s) to be mapped to regions of the chromosomes of the plant. This will acilitate the development of molecular markers that will make it possible for the student and subsequently Sakata, to track the resistance genes in later crosses between the offspring of crosses with the resistant plants and commercially acceptable plants. This will dramatically speed up the breeding of TuMV-resistant varieties. Using molecular markers to identify plants carrying the resistance genes for crossing will take hours, conventional means take months.