The role of the sexual cycle in escalating wheat rust diversity in the UK

Wheat rusts are a major threat to cereal production worldwide. As is common among rust pathogens, the wheat rusts require two hosts to complete their life cycles; stem and yellow rust undertake asexual reproduction on wheat and complete sexual reproduction on barberry (Berberis), where recombination can lead to emergence of novel genotypes. The eradication of barberry in the UK drove stem rust to almost complete extinction. However, over the past decade, barberry planting has been reinitiated and is advancing at speed in many major wheat growing regions. In the UK, this is largely driven by the habitat conservation programme for the endangered barberry carpet moth, Pareulype berberata. This is worrying because in the same time period we have seen an increasing number of sporadic stem rust epidemics in Europe, including severe outbreaks as far apart as Sweden and Sicily. Here in the UK in our preliminary study, we identified one wheat plant infected by stem rust in 2013 which illustrates the potential for stem rust to infect wheat crops in the UK. Furthermore, in 2017 we recorded for the first time in decades stem rust aecia on barberry in the UK. In parallel our collaborators in Sweden in the same year identified the first sexual population of wheat stem rust derived from barberry.

The overall aim of this project is to characterize the composition of rust on Berberis to determine if this mass re-planting could be facilitating the future re-emergence of stem rust in the UK, whilst also enhancing wheat yellow rust diversity. This will provide vital information for the future design and deployment of surveillance and management strategies that fully consider the threat of Berberis. However, it must also carefully balance the desire to minimise the risk of intensifying wheat rust diversity with (where possible) protecting habitat for the barberry carpet moth.

The proposed research aims to: (1) define the composition of rust on Berberis in the UK, (2), determine the risk of barberry-derived sexual rust populations to UK wheat and barley production, and (3) develop a UK risk model for wheat rust dispersal from Berberis and associated management actions. This research project will provide a wealth of information regarding the role of the sexual cycle in exacerbating the diversity of cereal rusts. Furthermore, it will provide vital information that will directly inform policy regarding the re-planting programme for Berberis across the UK and identify areas of high risk that should be avoided or (if plants are already present) regularly monitored. Herein, we aim to achieve a careful balance that manages the immediate needs of the farming community, ensures future resilience in UK wheat by accessing the susceptibility of breeding material to wheat stem rust, whilst conserving the biodiversity of UK fauna.

Stem and yellow rust are major threats to cereal production worldwide. Like many rust pathogens, they require two hosts to complete their life cycles, undertaking asexual reproduction on cereals and complete sexual reproduction on barberry, where recombination can lead to emergence of novel genotypes. The eradication of barberry in the UK drove stem rust to almost complete extinction. However, over the past decade, barberry planting has reinitiated in many major wheat growing regions. In the UK, this is largely driven by the habitat conservation programme for the endangered barberry carpet moth, Pareulype berberata. This research aims to characterize the composition of rust on barberry to determine if mass re-planting could facilitate the future re-emergence of stem rust in the UK, whilst also enhancing wheat yellow rust diversity.

The central hypothesis is that, in contrast to the position since c.1850, there is potential for rust aecia to play a significant role in generating new races, enhancing pathogen diversity and generating epidemics of wheat rust in the UK. The rationale is based on a preliminary study that provided the first evidence for many decades that wheat stem rust is present in the UK and could potentially be overwintering and infecting barberry. Furthermore, Sweden also witnessed the first report in Europe for decades in 2017 of a highly diverse sexual wheat stem rust epidemic that originated from barberry.

The proposed research will: (1) define the composition of rust on Berberis in the UK, (2), determine the risk of barberry-derived sexual rust populations to UK wheat production, and (3) develop a UK risk model for wheat rust dispersal from Berberis and associated management actions. Herein, we aim to achieve a careful balance that manages the immediate needs of the farming community, ensures future resilience in UK wheat by accessing the susceptibility of breeding material to wheat stem rust, whilst conserving the biodiversity of UK fauna.

PI Saunders will take the lead in managing the impact plan that will be an agenda item at monthly project meetings with Co-I Brown. Both researchers have excellent track records in communicating the outcomes of their research to a broad audience and sharing tools, resources and associated code in a free and open manner (e.g. crowdsourcing of ash dieback genomics). The PI and Co-I are regularly invited to speak about their research at national/international meetings and at various other venues.

Beneficiaries will include:

Those involved in wheat rust surveillance and management such as the UK Cereal Pathogen Virulence Survey (UKCPVS), which is funded by AHDB. They will benefit from establishing the role of the sexual cycle in generating new rust races in the UK. Throughout the project, information will be relayed to the UKCPVS as soon as relevant. PI Saunders is a regular speaker at their annual stakeholder meeting and Co-I Brown chairs the UKCPVS.

Researchers working with wheat rust disease. All data will be made freely available where practical, at the earliest possible opportunity for use by the wider scientific community. The data will initially be hosted via a project-specific website to ensure rapid release under a creative commons license (CC BY-NC-SA 3.0). Once submitted for publication all data will be deposited in public repositories and linked to via the project-specific website.

Breeders, farmers, agronomists and wheat variety testing authorities will benefit from new information regarding the resilience of current and future wheat varieties to rust infection through screens carried out in South Africa and Pakistan. In particular, assessments regarding general susceptibility to wheat stem rust in South Africa and for susceptibility to the more diverse populations of wheat yellow rust located in the Himalayan region. This may lead directly to decisions regarding the selection of future breeding material. This audience will also benefit from assessment of the risk to rust control posed by replanting of barberry and climate change. They will be reached as participants in our annual project meeting and through communication of results via relevant farming press outlets.

Researchers studying cereal rusts. The development of markers for Puccinia striiformis and P. graminis that are specific to the various formae speciales will be especially valuable. In particular, the KASPar markers (that can be more readily adopted by our breeding partners) will be of great interest to national pathogen surveillance programmes and rust researchers that are increasingly interested in evaluating the role of the sexual cycle in generating diversity for cereal rusts.

The general public, which will benefit from interactions with the PI and Co-I, who have given talks to public audiences (e.g. CropTec and Friends of JIC) on a variety of issues such as plant biosecurity. They will specifically focus on further educating the public on genome science and pathogen dispersal in relation to plant pathogens and the crops they infect. They aim to give one talk to a public audience (e.g. Science Café, Friends of John Innes) relating to this project, at least once per year throughout the project.

The PDRA's recruited for this project will benefit from improved skills, knowledge and experience gained from the research and wider training. This will contribute to their future economic activity in the public and/or private sectors. The innovative nature of the project is such that these individuals will likely develop unique skills that should prove highly attractive in the marketplace. This proposal also brings together an array of disciplines that will provide an exciting training ground for a cadre of excellent young scientists. The resulting innovation and training will provide the next generation of skilled crop scientists, with benefits beyond the immediate outcomes of this project.