Adaptation of the standard method by changing the leaf disc
underlay from filter paper to PUR plastic foam could successfully
prevent contamination by secondary microbes. However, the new
underlay also resulted in a low sporulation of downy mildew.
The physiological impact of B. lactucae infection could, nevertheless
be show by evaluation mean Fv/Fm. For a reliable detection of
susceptibility of plants to B. lactucae the pixel wise analysis of relative
proportion of Fv/Fm was applied. This appropriate algorithm
could distinguish resistant and susceptible butterhead and batavia
lettuce cultivars/lines. The proposed CFI technique can be successfully
applied to routinely evaluate B. lactucae susceptibility of butterhead
and batavia lettuce cultivars/lines.