Incidence of Lettuce Downy Mildew (Bremia lactucae) and Powdery Mildew (Golovinomyces cichoracearum) in Natural Populations of Prickly Lettuce (Lactuca serriola)

The study was focused on the wild pathosystem Lactuca serriola-lettuce downy mildew (Bremia lactucae) and lettuce powdery mildew (Golovinomyces cichoracearum). Observations were focused mainly on recording natural infection of prickly lettuce (Lactuca serriola) by downy and powdery mildews in the East Bohemia and Moravia (the Czech Republic) in the May-September period of 2007-2011, and on the influence of environmental conditions on disease incidence. Only data for July and August were used for the detailed comparisons of occurrence of both pathogens, because intensity of disease in this period was the highest. Data were linked with the average monthly temperature and rainfall rate in the Czech Republic. G. cichoracearum prefers rather low levels of precipitation and temperatures around 20 C, therefore significantly higher incidence of this pathogen was recorded in August 2007. On the other hand in July 2009 and 2010, when the intensities of precipitation were higher, incidence of Bremia lactucae prevailed. In August 2010 and 2011 incidence of both pathogens were more or less similar at all locations. Our observations showed that climatic conditions influence the incidence and prevalence of both pathogens in weedy growing populations of Lactuca serriola.