The degree of infection with B. lactucae and, occasionally contamination
of layers of filter paper with secondary microbial plaque
was daily evaluated by visual inspection. Downy mildew was
rated in following steps: appearance of first conidiophores, 5%
affection and at 10–100% disease severity in 10% steps. Contamination
was only recorded as ‘‘+’’ if existing or ‘‘’’ if there was none.