To reduce the pronounced effects of secondary microbial contamination,
which was observed on non-sterilized filter paper,
used as standard underlay in visual rating tests and also in the
previous experiment A, open PUR plastic foam was applied in
another experiment. PUR plastic foam largely prevented microbial
contamination but also seriously delayed the development of
Bremia infection. On the other hand, clear effects of infection could
be measured with CFI. This effect helped to clearly identify infection
pressure and plants responses to Bremia.