Within each Petri dish, the distribution of Fv/Fm among all leaf
discs of resistant lettuce lines was relatively even, irrespective of
inoculated or not (data not shown). In contrast, the local variability
of this fluorescence parameter largely increased with progressing
infection in susceptible lettuce lines (Fig. 1). In general, Fv/Fm of
inoculated leaf discs significantly declined only if the degree of disease
(dod) exceeded 5% as obtained by visual rating, irrespective of
the cultivar/line investigated (Fig. 2). Hence, detection limit for
analysis of Bremia infection by means of CFI can be assumed to