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

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.

Turnip yellows virus (TuYV) is a very important pathogen of vegetable brassicas (Brassica oleracea) and oilseed rape (OSR) in UK & Europe. Very high levels of infection have been detected in many crops. It reduces the yield of cabbage by upto 36% and Brussels sprouts by upto 65%. Estimates of OSR yield reduction in the UK are upto 30% (GBP 67-180 million/yr). The very common aphid Myzus persicae transmits TuYV.

The best insecticide seed treatments and sprays for TuYV control have been identified. Different cabbage and Brussels sprout cultivars have different susceptibilities to TuYV (all are susceptible, but some less so than others) and the earlier plants are infected, the greater the yield loss. A number of sources of extreme resistance have been found in B. oleracea and TuYV genetic diversity determined. Rothamsted Insect Survey has a network of suction traps around the UK trapping aphids including M. persicae which are identified and counted. They are also developing a molecular test to detect TuYV in the aphids.

These discoveries provide the opportunity to develop an integrated programme for optimal TuYV control. To develop the programme we intend to do field experiments in 2 regions of the UK. In the experiments we will apply the individual components (partial plant resistance, the best seed treatment and the best sprays) separately, in pairs and threes to quantify their efficacy. This will identify the best combinations and quantify synergy between treatments. The timing of spray treatments will be informed by suction and water trap catches.

To improve the integrated programme the best source of extreme resistance to TuYV will be crossed with a susceptible line. F1s will be tested for resistance/susceptibility to TuYV. A segregating BC1 population will be developed to map the resistance genes.

The project includes 2 research organisations, 2 agrochemical companies, 4 seed companies and an extension company facilitating extensive exploitation.

A broad range of stakeholders will benefit from the research - consumers, processors, growers, seed companies and agrochemical companies. The nation's health and wealth will also benefit.

Consumers will benefit from the reduced virus infection of brassica vegetables the project will deliver. Less virus infection will mean increased quality of brassicas, better security of supply and lower prices. More precise and less spraying that the integrated programme will facilitate will result in reduced insecticide residues in brassicas.

The processing industry will benefit through security of supply. Processors producing coleslaw from stored cabbage have turned away tonnes of cabbage due to tipburn caused by TuYV. Reducing TuYV in cabbage will reduce the amount of tipburn developing during storage, resulting in less waste and processors not having to buy cabbage from abroad at inflated prices. This will also result in less waste form the energy used to maintain stored cabbage at just above 0C for upto 8 months of the year.

Growers will benefit from having more options to control TuYV in the field. Having a decision support mechanism on when to use treated seed and the timing of sprays will take a lot of guesswork out of aphid and virus control resulting in much more effective insecticide use. This will reduce inputs, costs and residues and give better aphid and virus control, which in turn will increase profitability and security of supply. In the longer term having TuYV-resistant brassica varieties will help growers even more and reduce their reliance on insecticides, reducing costs and residues further.

Seed companies involved in the project will benefit from having a source of TuYV resistance they can introgress in to their commercial brassica varieties. The molecular markers developed in the research project will dramatically speed up the introgression for the seed companies. Being able to market TuYV-resistant brassica varieties should increase market share and improve the competitiveness of the seed companies and hence profitability.

The agrochemical companies involved will benefit from hard data on the effectiveness of their products in controlling aphids and TuYV in brassica field crops. Information on the best combinations of treatments and treatment timing based on a decision support mechanism will allow them to give better instructions and guidance to growers on the most effective way to use their products. This will improve their relationship with growers and result in more effective use of their products.

Brassicas are a nutrient-dense food containing a broad range of beneficial compounds especially protective against cancer and heart disease. Deployment of the integrated control strategy resulting in reduced virus infection, reduced pesticide residues, better quality vegetables and security of supply will be beneficial to the nation's health.

Warwick has a track record of engaging beneficiaries, promoting impact/delivery and exploiting advice and plant material. They are currently working with vegetable breeders to introgress the broad-spectrum resistance to TuMV in to commercial varieties. Together, they have developed a precise allele-specific marker for the gene retr01. Delivery of the resistance was further supported by a BBSRC CASE PhD studentship with the company. Rothamsted has a long history of providing and disseminating information on aphid abundance, flight times and insecticide resistance. The project outcomes will allow more growers to use the current information and provide new information on TuYV prevalence in flying aphids, which will be even more beneficial for growers.

The benefits of sustainable food production will be communicated to wider audiences through engagement activities, including professional bodies (CIKTN & Bioscience KTN, UK Dept for Business, Innovation & Skills [BIS], Forum for the Future, VeGin) and the schools outreach we are already engaged in.