Safeguarding UK hop production from Verticillium nonalfalfae: Using genomics to develop race-specific diagnostics and generate Verticillium resistant

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Rational: Highly virulent races of the soil borne fungus Verticillium nonalfalfae have substantially contributed to the decline of the UK hop industry. Once this lethal disease has established within a field it can only be combatted through this use of resistant varieties as there are no effective chemical means for control. Four V. nonalfalfae UK races have been characterised (mild, PV1, PV2, PV3), with two understood to have evolved exclusively in the UK. Published work has focused on identifying pathogenicity factors causing lethal wilt (PV1) on the susceptible cultivar 'Fuggle', a significant problem in continental Europe. By contrast, this PhD will investigate the resistance breaking UK races causing lethal wilt on the resistant cultivars 'Wye Challenger' (PV2) and 'Wye Target' (PV3).Approaches: WP1 Determining V. nonalfalfae population structure in terms of virulence characteristicsWP2 Fungal population genomics in relation to UK and EU virulence profiles WP3 Identification of race specific pathogenicity factors through comparative genomics for use in the development of diagnosticsWP4 Validation of pathogenicity factors through knockouts of candidate genes and Host Induced Gene Silencing (HIGS)Impact: Identifying regions of the genome unique to each V. nonalfalfae race structure will allow the generation of soil diagnostic tools to inform planting and management decisions in hop production. Whereas the use of HIGS and gene knockouts will validate pathogenicity factors and allow the generation of Verticillium resistant hop varieties. Existing funding has been secured to characterise novel sources of Verticillium resistance in hop through QTL mapping. However, understanding the race structure of UK V. nonalfalfae will allow the Wye Hops breeding company to develop robust disease resistant hop varieties. This project will complement current host work and contribute to understanding of the arms race between hop breeders and Verticillium.