Ralstonia solanacearum race 3 biovar 2, the causative agent of potato brown rot (bacterial wilt), is an economically important disease in tropical, subtropical and temperate regions of the world.

A study was performed in order to assess the presence of Xylella fastidiosa in imported ornamental plants, among them Olea europaea, Coffea arabica and Nerium oleander. Positive results were only obtained from C. arabica, where 15 plant samples tested positive for X. fastidiosa by PCR, nine from Costa Rica and six from Honduras. Transmission electron microscopy observations indicated that rod‐shaped bacterial cells exhibiting the characteristics of X. fastidiosa cells were present in the xylem vessels of leaf petioles obtained from the infected C. arabica plants. Diversity of X. fastidiosa in C. arabica plants was assessed through a multilocus sequence typing (MLST) analysis of seven housekeeping genes (leuA, petC, lacF, cysG, holC, nuoL and gltT) and compared with X. fastidiosa infecting different host plants worldwide. Based on this MLST analysis, the prevalence of different sequence types (STs) of X. fastidiosa in the C. arabica ornamental plants was demonstrated and related to different X. fastidiosa subspecies, underlining the risk of introducing additional genetic diversity for X. fastidiosa to Europe. ST53, related to X. fastidiosa subsp. pauca, was frequently found in these C. arabica samples. A second ST related to X. fastidiosa subsp. pauca, ST73, has been assessed in coinfection with ST53 in one individual plant. Additionally, ST72 and ST76, related to X. fastidiosa subsp. fastidiosa, have been recorded. Next to these previously described STs, a novel ST, namely ST77 has been revealed, related to X. fastidiosa subsp. fastidiosa. Isolation of X. fastidiosa from leaf petioles and midribs of infected C. arabica plants was successfully performed only after the application of an additional ultrasonication step during the extraction procedure. Based on this approach, a number of X. fastidiosa isolates were obtained and further characterized.

This paper describes a comparison study of test methods and supports the use of real-time polymerase chain reaction (PCR) for the detection of Clavibacter michiganensis subsp. sepedonicus and Ralstonia solanacearum in potato tubers in routine testing. These 2 bacteria are quarantine organisms under European Union (EU) regulatory control and testing for (latent) infections of these bacteria in seed potatoes is mandatory. Real-time PCR tests were performed on 276 routine potato tuber samples, including samples infected with either C. michiganensis subsp. sepedonicus or R. solanacearum, and the performance of these real-time PCR tests was compared with that of immunofluorescence (IF). Real-time PCR tests, using different primer sets and extraction and PCR protocols, proved to be sensitive and specific for the detection of C. michiganensis subsp. sepedonicus and R. solanacearum in potato tubers in routine testing, and performed at least as well as IF. Real-time PCR is a good addition to the detection protocols as laid down in EU regulations (EU Council Directives 2006/56/EC and 2006/63/EC).

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.

During the last two years, greenhouse cultivation of rose (Rosa spp.) in the Netherlands has been challenged by an uncommon bacterial disease. Affected plants suffered from chlorosis, stunting, wilting, and necrosis. The bacterial isolates obtained from the different Rosa spp. cultivars were all identified as phylotype I, sequevar 33 from the 'Ralstonia solanacearum species complex' (RSSC), actually reclassified as Ralstonia pseudosolanacearum. The work in this paper considers the genetic diversity and the phylogenetic position of 129 R. pseudosolanacearum isolates from the outbreak. This was assessed by AFLP based on four different primer combinations and MLP using partial sequences of the egl, mutS, and fliC genes. The AFLP revealed identical profiles for all the isolates, irrespective of their association with Rosa sp. propagating material, Rosa spp. plants for cut flowers, or water used in the different greenhouse cultivations. These AFLP profiles were unique and diverged from profiles of all other reference isolates in the RSSC included. Furthermore, MLP on egl, fliC, and mutS gene sequences clearly demonstrated that all R. pseudosolanacearum isolates clustered in phylotype I, as a distinct monophyletic group. Interestingly, this monophyletic group also included phylotype I strain Rs-09-161 from eggplant (Solanum melongena), isolated in 2009 in India. AFLP and MLP were both efficient in revealing the genetic divergence from the RSSC isolates included. The phylogenetic tree constructed from the AFLP profiles was, in general, in agreement with the one obtained from MLP. Both phylogenetic trees displayed a similar clustering, supported by high posterior probabilities. Both methodologies clearly demonstrated that the R. pseudosolanacearum isolates from Rosa spp. grouped in a monophyletic group inside phylotype I, with a particular correspondence to a strain present in India, as revealed in MLP.