Phylloxera-infested grapevines have reduced chlorophyll and increased photoprotective pigment content - can leaf pigment composition aid pest detection?

Grape phylloxera (Daktulosphaira vitifoliae Fitch) is a root-feeding pest of grapevines. In Australia, phylloxera-infested vineyards are subjected to quarantine restrictions and early detection remains vital for the timely implementation of post-outbreak quarantine protocols. Current detection methods rely on time-consuming ground surveying, which involves detailed examination of grapevine (Vitis vinifera L.) root systems. Leaf pigment composition is often a sensitive indicator of plant stress. The increasing popularity of remote sensing systems, which exploit those changes in pigments observed with plant stress, offers a real possibility for the development of a phylloxera-specific remote detection system. Our objective was to investigate changes in grapevine leaf pigments associated with phylloxera infestation and to relate any changes to appropriate reflectance indices. This was achieved with a glasshouse experiment in which the responses of two vine cultivars (Cabernet Sauvignon and Shiraz) to phylloxera infestation were compared with their responses to water and nitrogen deficiencies. The responses of leaf pigments to phylloxera infestation were also investigated in Pinot Noir and Cabernet Sauvignon grapevines grown under field conditions. A reduction in the leaf chlorophyll content and an increase in photoprotective pigment concentrations were observed in leaves of phylloxera-infested grapevines compared with uninfested vines. The photochemical reflectance index (PRI) was found to be most closely associated with the ratio of total carotenoid to chlorophyll in these vines.