Abstract
Grape phylloxera (Daktulosphaira vitifoliae) can infest both roots and leaves of Vitis species. In commercial vineyards planted with Vitis vinifera scions grafted on rootstocks, grape phylloxera infestation is generally limited to root feeding. Vineyards are, however, increasingly subjected to vineyard-wide foliar infestations that last throughout the growing season. While some vineyards are affected by the infestation pressure of external leaf-feeding populations, other annually affected V. vinifera vineyards do not have these in their vicinity. Much is known about the damage potential of grape phylloxera root feeding; however, data on how phylloxera leaf infestation affects V. vinifera grapevines in commercial vineyards are lacking. This study, therefore, aimed to assess whether grapevine growth and yield are affected due to leaf infestation as it occurred in three commercial vineyards in the study area. Treatments were based on phylloxera leaf infestation and additional defoliation. Single-leaf carbon acquisition was measured with gas exchange analyses on healthy and galled leaves. Pruning weight and internode length were measured to assess the effect of leaf infestation and the effect of plant growth and vigour on leaf gall outbreaks. Yield quantity and quality were measured, and grapes were vinified for sensory analyses. Furthermore, using enzymatic analyses, non-structural carbohydrates were analysed in perennial wood. A significant decrease in sugar content in grapes (10 %) and starch reserves in perennial wood (11 %) was found in the most heavily infested vineyard. Grape must of infested plants in another vineyard furthermore showed a significantly higher level of titratable acid (7.5 %). Significant infestation effects seen in one vineyard were not significant in the other two vineyards. No significant differences were seen for carbon acquisition, harvest quantity, wine sensory analysis, pruning weight or internode length. The overall effect of phylloxera leaf infestation in the studied vineyards was, therefore, marginal. Grapevine vigour did not differ between infested vines, insecticide-sprayed vines, and vines on which no leaf infestation outbreaks took place. By analysing phylloxera leaf infestation under field conditions, these preliminary results form a basis for future long-term field studies about phylloxera leaf feeding on Vitis vinifera within the context of other biotic and abiotic plant stresses.
Highlights
IntroductionGrape phylloxera (Daktulosphaira vitifoliae Fitch) (from here on phylloxera) is a destructive pest for global viticulture
Grape phylloxera (Daktulosphaira vitifoliae Fitch) is a destructive pest for global viticulture
In commercial vineyards planted with Vitis vinifera scions grafted on rootstocks, grape phylloxera infestation is generally limited to root feeding
Summary
Grape phylloxera (Daktulosphaira vitifoliae Fitch) (from here on phylloxera) is a destructive pest for global viticulture. This plant sap-sucking and gall-forming insect is an obligate biotroph of Vitis L. spp, on which it can infest both roots and leaves. Most plant damage is caused when phylloxera infests mature roots and creates tuberosities. When these are formed, the root vascular system is laid bare, disrupting water and nutrient flows and enabling the entry of soil pathogens (Niklowitz, 1954; Powell et al, 2013). Though nodosity feeding (root tip galling) does not pose this extent of host plant damage, it can amplify the extent of other biotic (Edwards et al, 2007) and abiotic (Savi et al, 2019; Savi et al, 2021) plant stresses. Root and leaf galls are known to impact the functioning of the grapevine, modifying primary and secondary host plant metabolism, to alter plant defences and promote carbon importation into the gall tissue (Eitle et al, 2017b; Eitle et al, 2019a; Eitle et al, 2019b; Griesser et al, 2015; Nabity et al, 2013)
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