Archivio Journal of Plant Pathology

Abstract:

Chlorophyll fluorescence, UV-induced fluorescence and reflectance signals of grapevine leaf tissue naturally infected by Plasmopara viticola were inspected in three susceptible grapevine cultivars (Cabernet Sauvignon, Pinot Blanc and Pinot Gris). Distribution of FV/FM parameter over the leaf was found to be effective to discriminate symptomatic and asymptomatic leaf tissue. Reduction of FV/FM parameter ~ 25% was found in all infected leaf spots. Infected leaves also expressed significantly changed chlorophyll fluorescence induction kinetics expressing much slower electron transport rate on donor and acceptor site of photosystem II. Symptomatic leaves emitted high fluorescence signal under UV excitation 320nm, centered at 395nm, emanated mainly from highly fluorescent compound 2,4,6-trihydroxyphenanthrene-2-O- glucoside. Increase of this compound was found in all inspected grapevine varieties, while its concentration was strongly dependent on resveratrol concentration. Concentration of trans- resveratrol ranged in asymptomatic leaves from 0.1μg·g-1 (CS) to 0.2μg·g-1 (PB, PG). Highest increase of trans-resveratrol in infected leaf tissue was found in PB (4.4μg·g-1), followed by CS (1.6μg·g-1) and PG (1.1μg·g-1). 2,4,6-trihydroxyphenanthrene-2-O-glucoside concentrations varied from 0.41 (PB), 0.75 (PG) to 1.01μg·g-1 (CS) in asymmptomatic leaves, since its concentration rapidly increase with severity of infection [71.09 (PB), 79.37 (PG), and 26.14 μg·g- 1 (CS)]. Reflectance vegetation indices SRI R750/R700, (R780-R710)/(R780-R680) and CRI700 were the most powerful to follow changes in chlorophylls and carotenoids contents under Plasmopara viticola infection. Infected leaves also exhibited lower chlorophyll a (~50 %) and carotenoids (~70%) content. Combination of these optical signals can be used as an effective, non-invasive tool for an early detection of Plasmopara viticola in field.