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

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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.