Volcanic impacts on peatland microbial communities: A tephropalaeoecological hypothesis-test

Volcanic eruptions affect peatlands around the world, depositing volcanic ash (tephra) and a variety of chemicals including compounds of sulphur. These volcanic impacts may be important for many reasons, in particular sulphur deposition has been shown to suppress peatland methane flux, potentially reinforcing climatic cooling. Experiments have shown that sulphur deposition also forces changes in testate amoeba communities, potentially relating to the reduced methane flux. Large volcanic eruptions in regions with extensive peatlands are relatively rare so it is difficult to assess the extent to which volcanic eruptions affect peatland microbial communities; palaeoecological analyses across tephra layers provide a means to resolve this uncertainty. In this study, testate amoebae were analysed across multiple monoliths from a peatland in southern Alaska containing two tephras, probably representing the 1883 eruption of Augustine Volcano and a 20th Century eruption of Redoubt Volcano. Results showed relatively distinct and often statistically significant changes in testate amoeba community coincident with tephra layers which largely matched the response found in experimental studies of sulphur deposition. The results suggest volcanic impacts on peatland microbial communities which might relate to changes in methane flux

PM 7/44 (2) Xanthomonas citri pv. citri and Xanthomonas citri pv. aurantifolii

International audienc

Ralstonia pseudosolanacearum: risico’s van de aanwezigheid van deze nieuwe Q-bacterie in het Nederlandse oppervlaktewater voor akker- en tuinbouwgewassen

Ralstonia solanacearum (fylotype II), de veroorzaker van bruinrot in aardappel (Solanum tuberosum), is een quarantainebacterie die sinds de jaren ’90 voorkomt in het Nederlandse oppervlaktewater. Bitterzoet (Solanum dulcamara), een inheemse wilde plant die langs waterwegen groeit, is ook een waardplant van de ziekteverwekker en speelt een belangrijke rol in de vermeerdering van de bacterie en de overleving tijdens de winterperiode. In het voorjaar komt de bacterie vanuit de besmette bitterzoet planten in het water terecht. De bacterie kan ca. 5 weken buitende plant in het oppervlaktewater overleven (Janse1996). Er wordt jaarlijks een grote survey uitgevoerdom besmetting van de Nederlandse watergangen inkaart te brengen (Janse et al. 2009). Vondsten kunnenleiden tot een beregeningsverbodsgebied; het oppervlaktewater in deze gebieden mag niet gebruikt worden voor de teelt van aardappelen en tomaten ziewww.nvwa.nl/onderwerpen/plantenziekten-en-plagen/bruinrot/verbodsgebieden-gebruik-oppervlaktewater). In 2020 werd tijdens deze survey in tweeafzonderlijke gebieden (omgeving Midden-Regge enomgeving Breukelen) niet R. solanacearum (fylotypeII), maar een andere Ralstonia soort aangetoond,namelijk Ralstonia pseudosolanacearum

Assessing the Pathogenic Ability of Ralstonia pseudosolanacearum (Ralstonia solanacearum Phylotype I) from Ornamental Rosa spp. Plants

Ralstonia pseudosolanacearum (Ralstonia solanacearum phylotype I) isolates found in stunted, yellowing, and wilted ornamental rose (Rosa spp.) were assessed for their pathogenic ability in two rose cultivars (cv. “Armando” and cv. “Red Naomi”) and in four solanaceous crops: tomato (Solanum lycopersicum cv. “Money Maker”), tobacco (Nicotiana tabacum cv. “White Burley”), eggplant (Solanum melongena cv. “Black Beauty”) and sweet pepper (Capsicum annum cv. “Yolo Wonder”). Significant differences were observed in susceptibility between the two rose cultivars as well as between the two modes of inoculation performed. The cultivar “Armando” was significantly more susceptible than cultivar “Red Naomi,” exhibiting higher disease severity and incidence. Similarly, stem inoculation after wounding was found to be significantly more effective than soil drenching, resulting in higher disease severity. Additionally, a temperature dependency in susceptibility was observed for both cultivars irrespective of the mode of inoculation, however, this was significantly more pronounced upon soil drenching. The solanaceous crops all showed to be susceptible to the R. pseudosolanacearum isolates originated from the Rosa spp. plants. Furthermore, both rose cultivars were able to harbor symptomless infections with other R. pseudosolanacearum and R. solanacearum isolates than those isolated from rose. Our results clearly demonstrated that latent infections in a rose cultivar such as cv. “Red Naomi” do occur even at temperatures as low as 20°C. This latency poses high risks for the entire floricultural industry as latently infected Rosa spp. plants are propagated and distributed over various continents, including areas where climatic conditions are optimal for the pathogen