Plasmopara viticola is an economically
important pathogen of grapevine. Early detection of
P. viticola infection can lead to improved fungicide
treatment. Our study aimed to determine whether
chlorophyll fluorescence (Chl-F) imaging can be used
to reveal early stages of P. viticola infection under
conditions similar to those occurring in commercial
vineyards. Maximum (FV/FM) and effective quantum
yield of photosystem II (ΦPSII) were identified as the
most sensitive reporters of the infection. Heterogeneous
distribution of FV/FM and ΦPSII in artificially
inoculated leaves was associated with the presence of
the developing mycelium 3 days before the occurrence
of visible symptoms and 5 days before the
release of spores. Significant changes of FV/FM and
ΦPSII were spatially coincident with localised spots of
inoculation across the leaf lamina. Reduction of FV/
FM was restricted to the leaf area that later yielded
sporulation, while the area with significantly lower
ΦPSII was larger and probably reflected the leaf parts
in which photosynthesis was impaired. Our results
indicate that Chl-F can be used for the early detection
of P. viticola infection. Because P. viticola does not
expand systemically in the host tissues and the effects
of infection are localised, Chl-F imaging at high
resolution is necessary to reveal the disease in the
field.
