Lettuce: biology and management of Fusarium wilt

Summary: Fusarium wilt of lettuce caused by Fusarium oxysporum f.sp. lactucae (FOL) results in severe losses in production areas globally. Four races occur, with race 1 being the most widespread in field and protected crops (USA, southern Europe). FOL was first reported in the UK in 2017, and genetic analysis at Warwick identified outbreaks were caused by FOL race4 (FOL4). FOL4 was initially reported in the Netherlands and Belgium and anecdotal evidence suggests it is more aggressive than FOL1, especially at low temperature. However, so far FOL4 is restricted to protected lettuce. Control of FOL4 is challenging as it produces long-lived chlamydospores and there is no varietal resistance available; consequently it represents a significant threat to the industry. This project will develop rapid molecular diagnostic tools for FOL4 detection/quantification which will aid monitoring of further outbreaks. These tools will also allow us to understand key aspects of pathogen biology such as infection, colonisation and survival on host/non-host plants. This will inform the potential use of rotation crops and/or fallow treatments for disease management. The effect of temperature and FOL inoculum level will also be examined to determine how these factors affect disease development. Finally, the potential of disinfectants and hot water/steam as hygiene treatments for trays and equipment will also be evaluated to provide growers with a means of minimising FOL spread. Industry representatives will be engaged during the project to ensure that results have direct application for growers/propagators, building on an extensive network already developed for the AHDB FOL technical review.

Aim: The main aims of the project are to develop molecular tools for FOL4 identification and quantification, understand key factors affecting FOL4 disease development and identify hygiene approaches to limit pathogen spread.

Objective: 

1. Develop tools for molecular detection and quantification of FOL / FOL4

2. Determine the effect of temperature and inoculum level on FOL4 disease development and the impact of non-hosts / fallow on FOL4 survival.

3. Test hygiene measures to eliminate FOL4 inoculum