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

Interlaboratory test performance studies for identification of Ralstonia solanacearum and molecular confirmation of its virulence : Euphresco Final Report

The EU directive 2006/63/EC describes a detailed protocol for the official testing of Ralstonia solanacearum, that is internationally recognized and has been implemented in many diagnostic laboratories across Europe and beyond. In this protocol, the confirmation of the identity of the bacterium is performed by a laborious, time-consuming and expensive pathogenicity test. Additionally, the described protocols involved in the official testing of Ralstonia solanacearum (for detection and/or identification) require a lot of time, a high level of quarantine measures, and a high degree of expertise. The aim of this project was to develop, and evaluate molecular diagnostic methods for the detection and identification of Ralstonia solanacearum and verification of its virulence that would be faster, more specific and robust. Based on the current taxonomic insights, the high degree of heterogenity present inside the Ralstonia solanacearum species complex (RSSC) has resulted in the clear distinction of three new species inside this complex; the requirement defined in this Euphresco project was that the new molecular tests could be optimally implemented for the detection and identification of Ralstonia solanacearum and Ralstonia pseudosolanacearum, but not of Ralstonia syzygii.The two main objectives of the project were:1) To identify Ralstonia solanacearum virulence genes, and subsequently develop a PCR test on those virulence genes. The development of such a test could substitute the pathogenicity test required by EU directive 2006/63/EC for complete diagnosis of Ralstonia solanacearum.2) To verify other molecular methods to detect or identify Ralstonia solanacearum strains. These methods include the real-time Loop-mediated isothermal amplication test (LAMP) and the recombinase-polymerase amplification assay (RPA)