SMART Bacteriophage Mixes: Sustainable Biocontrol for Onion Soft Rot

Globally, onions are the second-most popular vegetable, with an annual production of 99 Million tonnes. In the UK, they are the fourth-most consumed vegetable and growing in popularity, with recent lockdowns increasing the publics' perceived health benefits of eating vegetables and enthusiasm for home cooking. Currently, home onion production fulfils only ˜50% of UK demand (˜800kt p.a.), with the deficit made up by imports, mainly from The Netherlands but as far away as New Zealand, associated with greater environmental impact and higher overall prices, passed onto the customer.

**Our vision** is to allow UK growers to grow, store and supply onions to the UK market all-year-around, adding economic value and implementing more sustainable production methods. Improved-crop quality is key to increased productivity and this project will address bacterial-crop infections that produce significant in-store rots, resulting in crop right-offs, economic losses (£8.5M p.a.) and reputational damage. These losses tighten the UK supply, increasing the reliance on imports.

To date, a lack of detailed knowledge of the relevant onion-rot pathogens has hampered the development of effective rot-disease control, with the industry having access to relatively cursory identification methods. This project's **innovation focus** lies in using new pathogen-characterisation data to target control measures, bringing both economic and environmental added value to the UK-onion sector, in addition to being applicable to the £32.8Bn global market.

The **key objective** is to harness new knowledge of onion-rot pathogens to develop a sustainable, low-risk biological-control approach based on bacteriophage; naturally-occurring, highly-specific antimicrobial agents, which kill bacteria, with zero non-target effects. The lead partner has made considerable progress in developing the technology for plant protection but in relatively niche markets and with often limited pathogen characterisation extending development timelines. The biology and genetics of onion-rot pathogens and those from the wider-onion growing environment (microbiome) will be characterised, effectively creating a comprehensive library of the most prevalent and virulent onion-rot bacteria. This will act as a valuable resource for bacteriophage isolation and more focussed matching against key pathogens. The **aim** is to derive a pilot-bacteriophage formulation and investigate the feasibility of the rot-control approach, both in the laboratory, as well as in glasshouse and field investigations.

The project addresses a timely opportunity given the impact of rot-induced losses on the UK onion industry and the wider global opportunity. New methods of targeted-pathogen characterisation will also enable the lead SME to maximise commercialisation opportunities, within a rapidly-growing global biopesticide market.