Browsing by Person "Brandenburg, Elisa"

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Arthropods as possible vectors of grapevine trunk disease pathogens in German vineyards
(2025) Brandenburg, Elisa; Vögele, Ralf
The health of grapevines worldwide is highly threatened by grapevine trunk diseases (GTDs), which are caused by various fungal pathogens that colonize and destroy the vascular system of the vine wood. The esca disease complex is one of the most important GTDs. Typical symptoms are the characteristic "tiger stripe" patterns on leaves, gummosis, necrosis and white rot inside the vine wood as well as the sudden dying of individual shoots or even the entire vine. The ascomycetes Phaeomoniella chlamydospora and members of the genera Phaeoacremonium and Cadophora can cause the death of even young vines. Air currents and/or rain splashes carry the pathogenic spores to their entry points in the vine wood, which are mainly susceptible winter pruning wounds. The involvement of arthropods has also been described in South African studies. The aim of this dissertation was to determine and evaluate the risk of arthropod-mediated transmission of GTD pathogens for German vineyards. Over the course of two years (2019-2020), the spectrum of possible vectors was determined in two different vineyards and arthropod visits of presumably susceptible winter pruning wounds were documented using camera-based monitoring in April 2019. The presence of esca-related pathogens on the exoskeletons of various arthropods was examined using nested multiplex PCR. Of the total of 2099 samples, 35 %, 21 % and 7 % tested positive for Pa. chlamydospora, Phaeoacremonium spp. and C. luteo-olivacea, respectively. The European earwig (Forficula auricularia) and various spiders were the most common arthropods on vines, with frequencies of 30 % and 27 %, respectively. Under artificial conditions, it was confirmed that earwigs and black garden ants (Lasius niger) can transmit the pathogens Pa. chlamydospora and Pm. minimum to healthy potted vines. The potential of earwig feces as an inoculum source for Pa. chlamydospora and Pm. minimum was also discussed. Under artificial conditions, it was shown that the germination ability of the spores is not impaired by earwig gut passage and that healthy potted vines can be infected with contaminated earwig feces. However, fecal samples from earwigs collected in vineyards showed only a very low detection rate of at least esca pathogens. The number of Pa. chlamydospora spores on the exoskeletons of earwigs, ants and two jumping spider species collected in vineyards was determined by qPCR. The spore number was in 40 % of the samples that had previously tested positive for Pa. chlamydospora in the nested PCR below the detection limit of the qPCR. In 56 % of the samples analyzed by qPCR, fewer than 1000 spores were detected. Under natural conditions, a number of 100-2000 Pa. chlamydospora-spores is sufficient to infect susceptible wounds in the vine wood. In this work, the mycobiome of the surface of the exoskeleton of earwigs collected in vineyards was analyzed for the first time. Nine GTD-associated genera were detected, of which Phaeomoniella and Eutypa were found to have relative abundances of 6.6 % and 2.8 %, respectively. This could indicate a possible involvement of earwigs in the dissemination of esca and eutypiosis. The present investigations have shown that arthropod-mediated transmission of GTDs, especially esca pathogens, is theoretically possible in vineyards. However, the practical relevance of this fact seems low compared to the numbers of airborne spores of the pathogens, especially Pa. chlamydospora, detected during the presumed period of susceptibility of winter pruning wounds. In addition, the simultaneous occurrence of susceptible winter pruning wounds and potential vectors in the field is only present with late-pruned vines, while the risk of wounds during the growing season requires a more detailed assessment. The results of this work underline the importance of protecting all types of wounds in the vine wood in order to reduce the invasion of pathogens.