density-curves. All Fv/Fm-pixel values were allocated to ‘‘efficiency
classes’’ of photosynthetic activity at steps of 0.05. In addition, they
were accumulated to a ‘‘cumulative Fv/Fm’’ (%), starting from the
lowest values (0.00) and ending with 0.84. This was done individually
for each leaf disc. When the proportion of low Fv/Fm classes is
high (e.g. at 0.3), then infection is assumed to be successful and the
respective cultivar is indicated as potentially susceptible.