Developing integrated approaches for pest and disease control in horticultural field crops (IAPAD)

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Turnip yellows virus (TuYV) is a very important pathogen of vegetable brassicas (Latin name Brassica oleracea; cabbage, cauliflower, Brussels sprout, broccoli etc.) and oilseed rape (OSR) in the UK & Europe. Many crops sampled have had very high levels of TuYV infection. Unlike many viruses, TuYV does not cause very obvious symptoms in most brassicas (storage cabbage where it causes tipburn is the exception). This has meant many growers are unaware of the infections. Despite lack of obvious symptoms we showed that TuYV reduces the yield of cabbage by upto 36% and Brussels sprouts by upto 65%. Estimates of OSR yield reductions in the UK alone are upto 30% (losses of GBP 67-180 million/annum). TuYV can move between vegetable brassicas, oilseed rape and weeds, resulting in the high levels of infection of crops seen.A very common greenfly (peach-potato aphid) transmits TuYV; once they acquire the virus they transmit for life. In glasshouse experiments we have identified the best insecticide seed treatments and sprays for controlling TuYV. We have also shown in the field that different cabbage and Brussels sprout cultivars have different susceptibilities to TuYV (all are susceptible, but some less so than others) and that the earlier plants are infected, the greater the yield loss. We have also found a number of sources of extreme resistance to TuYV in Brassica oleracea and have been studying the diversity of TuYV by determining the genetic code of many isolates. Collaborators in the project have a network of suction traps around the UK that trap flying greenfly. They identify the different greenfly species including the peach potato aphid and count them. They are also developing a molecular technique to detect TuYV in the greenfly.All these discoveries provide the opportunity to combine them in to an integrated programme that will give optimal control of TuYV. To develop this integrated control programme we intend to do field experiments in two regions of the UK. At one location we will introduce greenfly carrying TuYV to provide high infection pressure and at the other location we will rely on natural infection. In these experiments we will apply the individual components (partial plant resistance, the best seed treatment and the best sprays) separately, in pairs and in threes in order to quantify the efficacy of individual and combined treatments. This will identify the best combinations and quantify synergy between treatments.The timing of spray treatments will be informed by when peach-potato aphids are flying, this will be known from the suction trap and water trap catches around the experiment.To build on and improve the integrated programme we will identify the best source of extreme resistance to TuYV in our resistant B. oleracea lines. This will be crossed with a susceptible line. The offspring will be tested for resistance/susceptibility by challenging plants with TuYV and testing for TuYV using a quantitative test called ELISA. Some of the next generation of plants will be susceptible to TuYV and some will be resistant. By analysing the genes/chromosomes/RNA/DNA of these plants and comparing this with the susceptibility/resistance status of the plants, it will allow the development of molecular markers. Seed companies will use these to significantly speed up the incorporation of the resistance genes into commercially acceptable varieties. We are collaborating with Syngenta and Dow in the optimal use of seed treatments and sprays and with the seed companies Tozer, Sakata UK, Enza Zaden and Rijk Zwaan UK on the TuYV resistance exploitation. We are also working with Allium and Brassica Agronomy who work with farmers. Through these collaborations the outcomes of the research (integrated programme for TuYV control and new sources of resistance to TuYV) will be exploited by growers in order to reduce residues in vegetables and inputs and increase yields, thereby contributing to food security.