Understanding population diversity of Bremia lactucae in the UK

Lettuce downy mildew is a foliar disease caused by Bremia lactucae, that results in reduced quality, yield and marketability of lettuce crops. This disease is more prevalent in cooler climates, such as the UK and is currently managed through a combination of routinely sprayed fungicides and host resistance. Understanding the population diversity both genotypically and phenotypically would allow for more informed decisions on crop breeding along with fungicide and resistance gene stewardship.  Appropriate tools are required to analyse a pathogen population and to detect pathogen presence.  Simple Sequence Repeat (SSR) markers are widely used in pathogen population monitoring, providing a good resolution for distinguishing genotypic differences between species and isolates of the same species in a given population. However, there are currently no SSR marker multiplexes developed to monitor B. lactucae. The International Bremia Evaluation Board (IBEB) collaborates to identify new races of B.  lactucae that may threaten the lettuce industry and has developed standardised systems of determining virulence of B. lactucae with a host differential assay and defined race denomination. If these phenotypic traits can be linked to genotype it would aid immensely in management decisions.  Therefore,  analysing  phenotypic characteristics and genotype of the contemporary population is an aim of this project. This project also aims to validate a detection assay (rt-LAMP) for B. lactucae in a commercial field environment, to determine threshold values and to analyse utility in providing an early warning of B. lactucae infection to growers.

The aims are:

• To develop Simple Sequence Repeat (SSR) markers to analyse lactucae populations,
• To link genotype to phenotype in lactucae,
• To validate a lactucae detection test, to provide outbreak information to growers to improve integrated management of lettuce downy mildew.