Figure 6

Localization of phenolic compounds, flavonoids and lignin in infected leaf tissues. Sensitive (a,b,e,f,i,j) and resistant (c,d,g,h,k,l) leaves have been inoculated with P. viticola. Phenols (a,c) and lignin (i,k) are visualized in bright field microscopy following nitrous reaction and phloroglucinol-HCl staining respectively, whereas flavonoids (e,g) and pathogen structures (b,d,f,h,j,l) in fluorescence microscopy following Wilson reaction and aniline blue staining respectively. (a) Phenolic compounds (red) on palisade cells of cv Chardonnay at 5 dai. (b) Wide diffusion of P. viticola mycelium inside the same tissue showed in (a). (c) Phenolic compounds (red-brown) inside the spongy mesophyll cells in close proximity to a failed penetration site. Hybrid Bianca at 5 dai. (d) Sporangia (s) and germinating zoospore (arrow) on the leaf epidermis showing fluorescent cells (asterisk), indicative of cell death. (e) Absence of a specific reaction to Wilson reagent in cv Chardonnay at 5 dai. (f) Regular diffusion of the mycelium in (e) sample. (g) Specific reaction to Wilson reagents (orange) inside the spongy mesophyll cells of cv Chardonnay at 5 dai. (h) Infected stoma covered by callose and poorly fluorescent, probably degenerating, P. viticola mycelium (m) with haustorial necks clearly visible in the same area showed in (g). (i) Presence of lignin (red-brown) inside the leaf veins of hybrid 18048 at 15 dai. (j) Wide diffusion of the pathogen inside sample (i). (k) Lignin on the host cell walls and inside cytoplasmic vesicles in the cells surrounding an infected stoma. Bianca at 15 dai. (l) Absence of mycelium, probably degenerated, inside (k) sample.