Grape phylloxera meets drought: increased risk for vines under climate change?

Abstract

Context and purpose of the study ‐ Climate change is increasing the frequency and severity of drought periods leading to significant impacts on agro‐economic activities, with particular regard to viticulture. Moreover, in the last decades the wine‐making industry is further threatened by new outbreaks of grape phylloxera (Daktulosphaira vitifoliae Fitch) which have been reported worldwide. Phylloxera is a galling aphid native to eastern North America that targets grapevines as its single host and source of nutrition. Knowledge on how the aphid affects the whole‐plant physiological functions is limited, in particular when the phylloxera attack is accompanied by drought stress. In the light of prolonged drought periods forecasted for the near future in many viticultural regions, it is fundamental to understand and predict eventual negative cumulative effects of a combined biotic‐abiotic stress.

Material and methods ‐ In the present study we monitored water and carbon metabolism, gas exchange and photosystem functionality of grapevines subjected to drought stress (D) and/or phylloxera infestation (P). The experiment was carried out in pots using Riesling grafted on Teleki 5C (RR) and own‐ rooted Teleki 5C (5C, rootstock). P vines were root inoculated with phylloxera eggs collected from a field population. A subset of plants was subjected to an 8 week‐long moderate drought stress (PD), while the others were maintained in well‐watered conditions (PI). Non‐inoculated control plants were also included in the trial for both irrigated (CI) and drought stress (CD) conditions. Non‐structural carbohydrates (NSC) were measured in young leaves developed under the treatments. Differences in root infestation (presence of nodosities) were also investigated among experimental treatments.

Results ‐ Drought stress had a significant impact on the plants gas exchange leading to the reduction of NSC in the leaves. On the other hand, infestation with phylloxera did not induce notable shifts in physiological traits with the exception of a marked increase of leaf surface temperature recorded in RR (+1°C recorded in P plants compared to C). The insect induced starch depletion and enhanced glucose synthesis in the leaves. The inoculation efficiency was higher in D plants compared to I ones, suggesting that events of water shortage favor the insect spread.