Browsing by Person "Haag, Nicolai"

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Grapevine Trunk Diseases : Epidemiologie und Molekulardiagnose wichtiger Esca-Erreger während der Pflanzguterzeugung
(2018) Haag, Nicolai; Vögele, Ralf
Esca is one of the most important grapevine trunk diseases (GTDs) worldwide. In Europe, the wood-inhabiting fungi Phaeomoniella chlamydospora (Pch), Phaeoacremonium aleophilum (Pch) and Fomitiporia mediterranea (Fmed) are considered the main causal agents of this disease. Even young vineyards and planting material can be affected by pathogens of Esca. So far, control possibilities were mainly limited to prophylactic measures, such as prevention of overly large pruning wounds, minimizing stress of affected grapevines and elimination of dead wood. By now, biological control is basically possible; its efficacy however, still remains to be fully proven under practical conditions. According to previous studies in Germany investigating the infection status of planting material, Pch is considered the most important causal agent for an early infection in grapevine nursery propagation. Based on this, the objective of the present study was to comprehensively assess the occurrence of Pch and other GTD-pathogens in grapevine wood and potential inoculum sources and to visually evaluate Esca-associated symptoms in rootstocks and scions during the propagation process including indoor working steps and the outdoor rooting phase. The results should then be used to point up possible control measures. For this purpose, from 2014 to 2016 visual ratings of Esca-associated wood symptoms were conducted on grapevine material collected from three different nurseries over the entire propagation process as well as from planting material ready for sale. Further assessments on pathogen occurrence by nested PCR and traditional culturing methods focused on rootstock material, which is more affected from experience, and were at first limited to the detection of Pch. For each year, a strong increase of wood symptoms, both in rootstocks and scions, was observed in the course of the production process. Compared to that, PCR- and culture-based detection rates of Pch in rootstock wood were considerably lower revealing a marked discrepancy between symptom incidence and the actual presence of the pathogen. Interestingly, a previously unconsidered fungus, Caophora luteo-olivacea (Clo), which is suspected to be a further GTD-pathogen, was frequently isolated from symptomatic rootstocks. Based on this observation, a multiplex nested PCR method was subsequently developed to specifically detect Pch, Clo as well as species of the Esca-relevant genus Phaeoacremonium (Pm). By using this method, Pch and Pm spp. were detected in ~9% and ~15% of tested rootstocks, respectively (average of all nurseries and years of observation), whereas detection rates of Clo were comparatively high at ~78%. This way, it was possible to harmonize previously observed discrepancies between symptom and pathogen incidence to a great extent. Regarding the occurrence of pathogens and expression of wood symptoms significant differences between nurseries were noticed at single sampling dates, in general however, infestation situations were quite similar. Further investigations were conducted to identify potential inoculum sources in the propagation process. Herefore, sampling was done from various hydration tanks, callusing media and nursery soil. In addition, spore traps were installed in nursery fields in order to monitor airborne inoculum. Samples were subsequently analysed by multiplex nested PCR and/or fungal isolation. PCR-based detections of Pch, Pm spp. and Clo were obtained from hydration tanks as well as from callusing media and air with Clo being the most common species in every respect. Furthermore, viable inoculum of Pch and Pm spp. were found in rootstock wood only, whereas Clo could be additionally isolated from hydration tanks, callusing media and nursery soil. However, isolation rates of Pch, Clo and Pm spp. respectively corresponded to only ~9%, ~9% and ~2% of the detection frequencies when using multiplex nested PCR. The present study allowed for a comprehensive and in part previously unknown insight into the infestation situations of planting material regarding Pch and further Esca-associated pathogens. It provides specific information on potential inoculum sources in grapevine nursery propagation and emphasizes the possible role of pre-infected planting in the development and spread of Esca. With respect to a targeted control of Esca and associated diseases, the obtained results provide an important basis to verify efficacy and practicabilty of existing or yet to be developed control measures.