Paul Hand and David Pink, from HRI Wellesboume continue this series of scientific features by considering the sustainable use of host resistance to downy mildew of lettuce. Most lettuce growers would agree that downy mildew, caused by Bremia lactucae, is the most important disease of lettuce in the UK. Infection results in loss of yield but more importantly loss of quality since susceptible plants develop chlorotic lesions on leaves with profuse sporulation on the underside of the leaf. A combination of resistance breeding and chemicals are currently used to control the disease and according to Defra the majority of fungicide applied to UK lettuce is for downy mildew control. However, the pathogen has evolved insensitivity to the fungicide metalaxyl, which limits the effectiveness of this approach.
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