Phylloxeration effects on the sink activity and assimilation rate in phylloxera (Daktulosphaira vitifoliae Fitch) infested grapevines (Vitis spp.)

Grape phylloxera (Daktulosphaira vitifoliae Fitch) induces root galls on tips of susceptible and partially resistant rootstocks. The monophagous parasite affects the host by inhibition of water- and mineral uptake, sink-source translocation, changes in secondary metabolisms and manipulation of root growth. Grafted phylloxerated vines rarely show severe plant damage. Compensation effects on leaf galled vines have been proposed, however no information is available for root galled vines. In two experiments we aimed to determine effects of root phylloxeration on the primary metabolism of Vitis spp. We hypothesise that affected vines respond with a compensation strategy consisting of an increased root growth, leaf respiration and photosynthetic activity. Experiment 1 was conducted to analyse phylloxeration effects on carbohydrate mobility within grafted vines (V. vinifera L. ‘Pinot Noir’ on SO4). Experiment 2 analyzed potential phylloxeration effects on vines under nitrogen deficiency on Teleki 5C (V. berlandieri × V. riparia). Assessed parameters included plant phenology, quantitative plant growth, levels of macro and micro nutrients, photosynthetic activity, gas exchange and activity of enzymes related to carbohydrate mobility (sucrose synthase, vacuolar invertase, cell wall invertase). Our results showed an increased root mass in combination with elevated carbon and nitrogen levels in the root system of phylloxerated vines. Gas exchange and enzymatic activity of enzymes related to carbohydrate mobility were increased upon phylloxeration. However shoot and berry growths were not reduced. In conclusion these results show that more carbohydrates are imported in the root system upon phylloxeration without reductions of shoot and berry growth indicating a compensation strategy of the host. However it is unclear whether grape phylloxera actively triggers the import of carbohydrates to the root system by potential effectors or the host counteracts the lack of nutrients withdrawn by the parasite.