Yellow Wheat Blossom Midge (YWBM) is a poorly understood and often under-reported insect pest of wheat, the UK's most widely grown crop. Midge larvae feed on the wheat flower, preventing grain formation and leading to significant yield losses. All wheat varieties are reported to be susceptible to this pest. In some years, the ideal conditions required for adult midges to emerge from dormancy in the soil, mate and lay eggs occur just as the wheat is at its most vulnerable to attack. However, YWBM damage varies from year-to-year and is currently difficult to predict. This project aims to further our knowledge of this pest and its impact on the wheat crop. In related pest midges, adult females produce a volatile sex pheromone which allows adult males to locate females prior to mating. Synthetic versions of these pheromones released from simple traps are widely used in many crops to monitor midge pests and identify when and where control strategies must be applied. By identifying the sex pheromone of YWBM in this project, we will have completed the necessary first step in developing an appropriate monitoring tool for use in UK wheat crops. We have previously identified experimental NIAB wheat lines that showed no YWBM damage in seasons when midge levels were high in adjacent varieties. With help from plant breeding companies, we will test these promising lines more thoroughly. We will grow them in small field plots at several locations across the UK, and measure YWBM levels in resistant NIAB lines and in susceptible commercial varieties. We will collect unripe wheat ears containing live YWBM larvae, and soil samples containing dormant pupae, from these and other sites to provide a source of midges. Young midges will be reared individually at NIAB East Malling until they emerge as adults. NIAB and NRI specialists will collect the volatile chemicals produced by groups of adult males and females. Through electrophysiological experiments at NRI, we will identify which chemicals produced by female midges can be detected by the males as likely components of the sex pheromone. Using chemical analysis and our experience in identifying other midge pheromones, we will begin identification of the YWBM sex pheromone components. If supply of midges and time allows, we will synthesize these likely components for further testing. NIAB will also explore the feasibility of maintaining a laboratory colony of YWBM for future work into the life cycle of this important pest.

Use of host resistance is the most effective and environmentally friendly way to control plant diseases. Oilseed rape (Brassica napus) is an important arable crop in the UK. The disease phoma stem canker, caused by Leptosphaeria maculans, poses an increasing threat to sustainable production of this crop. In the UK, phoma stem canker cause losses of > £100M p.a., despite use of fungicides. These losses will increase if the most effective fungicides are no longer permitted by EU legislation. Furthermore, it is predicted that global warming will continue to increase the range and severity of phoma stem canker epidemics. There is thus a challenge to produce cultivars with effective resistance in a changing climate to contribute to national food security. This project aims to decrease future risk of severe phoma stem canker on oilseed rape by developing a scheme for effective use of host resistance and by improving understanding of operation of host resistance against the pathogen to guide resistance breeding. The two types of resistance to L. maculans identified in B. napus are major resistance (R) gene mediated qualitative resistance that operates in cotyledons and leaves in autumn and quantitative resistance that operates in leaf stalk and stem tissues, after initial leaf infection until harvest in summer. R gene mediated resistance to L. maculans is single-gene race-specific resistance that is effective in protecting plants only if the corresponding avirulent allele is predominant in the local L. maculans population. R gene resistance often loses its effectiveness in 2 to 3 years after widespread use in commercial cultivars because of changes in L. maculans populations. To maintain the effectiveness of R gene resistance and decrease the risk that it will become ineffective, races in L. maculans populations in different regions will be determined. The L. maculans race information will be used to develop a scheme for deployment of cultivars with different R genes in space and time. Previous work at Rothamsted showed that temperature influences the effectiveness of both R gene resistance and quantitative resistance against L. maculans. To identify effective resistance in oilseed rape that will operate against L. maculans in a changing climate, this project will assess effectiveness of different types of resistance in both in controlled environments and natural conditions. Cultivars with only R genes, only quantitative resistance or combinations of R gene & quantitative resistance will be tested in different environments. From the results, we can assess which R gene or which combination of resistance is more effective. This information can be used to improve breeding strategies. To understand how temperature influences the effectiveness of host resistance, this project will focus on the three R genes which show a differential response to temperature; two of them map in the same region on chromosome A10 at distinct loci. To investigate mechanisms of operation of R gene and quantitative resistance against L. maculans, sets of materials with these R genes in the same background or the same R gene in different backgrounds will be used. These materials will enable us to investigate whether the difference in temperature response between these three R genes is due to the resistance loci or host background. Results from this project will help to minimise the risk of severe epidemics on oilseed rape so that yields are maintained to contribute to national food security and avoid unnecessary fungicide use. Breeders will benefit from improved strategies for breeding cultivars with effective disease resistance. The environment will also benefit from reduced greenhouse gas emissions through improved disease control in oilseed rape.

Nitrogen fertiliser is essential to sustain wheat yields but is also an important determinant of grain quality. This is because nitrogen is required for the synthesis of grain proteins, with the gluten proteins forming the major grain protein fraction. About 40% of the wheat produced in the UK is used for food production, particularly for making bread and other baked products. Wheat is also widely used as a functional ingredient in many processed foods, while bread wheat and imported durum wheats are used to make noodles and pasta, respectively. The gluten proteins are essential for these uses, providing visco-elastic properties to dough. Consequently, the content and quality of the grain proteins affect the processing quality, with a minimum of 13% being specified for the Chorleywood Breadmaking Process (CBP) which is used for over 80% of the "factory produced" bread in the UK. The requirement of nitrogen to produce wheat for bread making is also above the optimum required for yield, and farmers may apply up to 50 kg N/Ha above the yield optimum to achieve 13% protein (2.28% N). This is costly with nitrogen fertiliser contributing significantly to crop production, and may also contribute to a greater "nitrogen footprint" in the farmed environment. It may be possible to reduce the requirement for breadmaking wheats, to a limited extent, by optimising the efficiency of nitrogen uptake and use within the wheat plant. However, this will only have limited benefits and a more viable long-term solution is to develop new types of wheat and processing systems which will allow the use of lower protein contents for bread making. We will therefore identify types of wheat which have good and stable breadmaking quality at low grain protein. Genetic analyses of the trait will provide molecular markers to assist wheat breeders while studies of underpinning mechanisms will allow new selection procedures to be used to identify germplasm and select for quality in breeding programmes. We will also work with millers and bakers to establish optimum conditions for processing of wheats with lower protein contents.

Although oilseed rape (OSR; Brassica napus) has traditionally been grown as the most profitable break crop, a loss of controls for cabbage stem flea beetle (CSFB; Psylliodes chrysocephala), has resulted in UK cropping area declining by 35% between 2012 and 2019. The National Farmers Union (NFU) estimate the removal of neonicotinoid seed treatments has cost farmers ~£94 million/year in lost opportunity and crop loss. Additional costs have been absorbed by the UK crushing industry because of the need to import OSR. Collectively, this poses a serious risk to the viability of the UK OSR industry and current farm crop rotation practices. With the withdrawal of chemical controls, resistant cultivars are central to supporting Integrated Pest Management (IPM) strategies. However, unlike plant-pathogen interactions, our understanding of the interactions between host plants and chewing insects is limited. CSFBs are attracted to glucosinolates, chemicals used by Brassica species to deter non-specialist insect pests. Even if B. napus has defence or resistance mechanisms that deter CSFB feeding, the genetic control of such mechanisms and whether they can be exploited to breed for resistance has remained an open question. There are no known examples of resistance in B. napus and little knowledge of resistance mechanisms within our UK crop species. No resistant cultivars are currently available for any insect pest of OSR. This proposal builds on preliminary data using controlled feeding studies and field trials, which shows that variation for reduced adult CSFB feeding is present within a diverse panel of B. napus. The panel, comprising historical varieties of winter and spring OSR, Chinese OSR, swede and kale, contains genetic diversity which is unlikely to be present in elite cultivars. This has enabled us to identify loci associated with CSFB feeding damage. Controlled larval infestation studies within this population have also identified variation in the numbers of emerging adult CSFB, demonstrating the presence of resistance to CSFB larvae. Together these observations indicate that some varieties of B. napus carry genes which can 1) deter adult CSFB feeding and 2) confer resistance against larval infestation or reduce larval fecundity. If identified, this variation can be exploited to breed OSR resistant to both damaging stages of CSFB. This proposal developed by two research institutes (JIC and Rothamsted Research), seven major plant breeders and the OSR growers' Levy board (AHDB), aims to discover loci associated with adult CSFB feeding and larval resistance in B. napus. In parallel, we aim to develop an understanding of crop adaptations which affect OSR-CSFB interactions. This will be coupled with larval development studies, gene expression analysis and metabolite profiling to further elucidate key mechanisms by which Brassica plants identify and defend themselves against beetle attack. Key genes implicated in resistance and defence responses will be investigated using candidate gene studies in model plants, including candidate genes which underlie two loci implicated in the supporting data. Collectively, this knowledge, combined with germplasm and markers that will be used by participating breeders to integrate resistant alleles into commercial breeding pipelines, will facilitate the introduction of tolerant varieties into the UK OSR market.

Wheat is the UK's major food crop. A major constraint on wheat production is the disease yellow rust (YR), caused by the fungus Puccinia striiformis f.sp. tritici (Pst), with yield losses up to 50% in untreated crops. The two major control measures for this disease, used in combination, are use of resistant varieties and application of fungicides. Fungicide application is effective but expensive, limited by weather conditions and increasingly restricted in use due to environmental concerns. Host (i.e. wheat) resistance can also be very effective, with several known resistance genes conferring immunity to known races of Pst. However, populations of the pathogen regularly change and resistance genes suddenly become ineffective when the pathogen mutates. In Europe, there was a recent rapid incursion of an exotic Pst population, which is much more diverse than the established population it has displaced. As a result, there have been dramatic and ongoing changes in the patterns of YR resistance in commercial wheat varieties. In 2016 alone, seven varieties on the UK wheat Recommended List had their resistance ratings substantially reduced, with significant cost impact on growers. Breeding improved wheat varieties with effective, long-lasting YR resistance to withstand current and future incursions is now a top priority for northern European (NE) wheat breeders. In Yellowhammer, we will employ a strategy based on detecting and utilizing multiple race non-specific adult plant resistance (APR) genes, for long-term genetic control of the disease. These genes usually confer partial resistance, are characterized by reduced and slower pathogen growth, and can be 'stacked' with each other or with 'major" genes in the same plant to provide effective long-lasting resistance. We previously identified several APR genes - but finding the most effective combinations is challenging as different genes interact with each other in complex ways. To address this challenge, we are collaborating with seven NE breeding companies and the UK's Agriculture and Horticulture Development Board to develop experimental wheat populations based on elite European varieties, but which differ in the combinations of YR APR genes they carry. We will use these to: 1. Identify the most effective combinations of APR genes, and the times of the season they become effective, in field tests at twelve sites in NE over four years. We will investigate what is the most effective combination of strong and weak APR genes to achieve YR resistance in wheat. We will also determine the effectiveness of APR genes in hybrid wheat and any side-effects APR genes have on grain yield. 2. Determine, using 'microphenotyping', the timing and location of action in the plant of different APR genes involved in the pathogen-host interaction, helping us select functionally complementary APR genes to combine. 3. Identify which wheat genes and genetic pathways are switched on or off in response to the pathogen in the presence of different APR gene combinations in order to understand how to best assemble APR gene combinations with complementary molecular genetic mechanisms of resistance. We will also conduct field pathology trials of newly available populations and varieties to identify new APR genes. The results will allow us to determine the best combinations of resistance alleles to stack, and provide new genetic markers to aid the process. Results will be validated in active commercial breeding material and will immediately be translatable into the breeding programs of our commercial partners, enabling them to breed more durably resistant wheat varieties equipped to resist the current Pst population and potential future incursions. This will improve UK arable production and food security, and reduce environmental harm, as farmers benefit from having access to more consistently performing, longer-lasting varieties with reduced fungicide requirements.