Ralstonia solanacearum

Ralstonia solanacearum is an aerobic non-spore-forming, Gram-negative, plant pathogenic bacterium. R. solanacearum is soil-borne and motile with a polar flagellar tuft. It colonises the xylem, causing bacterial wilt in a very wide range of potential host plants. It is known as Granville wilt when it occurs in tobacco. Bacterial wilts of tomato, pepper, eggplant, and Irish potato caused by R. solanacearum were among the first diseases that Erwin Frink Smith proved to be caused by a bacterial pathogen. Because of its devastating lethality, R. solanacearum is now of the more intensively studied phytopathogenic bacteria and bacterial wilt of tomato is a model system for investigating mechanisms of pathogenesis.Ralstonia was recently classified as Pseudomonas with similarity in most aspects, except that it does not produce fluorescent pigment like Pseudomonas. The genomes from different strains varies from 5.5 Mb up to 6 Mb, roughly being 3.5 Mb of a chromosome and 2 Mb of a megaplasmid. While the strain GMI1000 was one of the first phytopathogenic bacterias to have its genome completed, the strain UY031 was the first R. solanacearum to have its methylome reported. Within the R. solanacearum species complex, the four major monophyletic clusters of strains are termed phylotypes, that are geographically distinct: phylotypes I-IV are found in Asia, America, Africa, and Oceania, respectively. R. solanacearum was once considered as a possible biological control of Kahili ginger (Hedychium gardnerianum), which is a member of '100 of the World's Worst Invasive Alien Species' in 2004. However, R. solanacearum is no longer used as a biological control for Kahili ginger in Hawaiian forests because of its wide host range. The ginger strain infects numerous ginger species, including edible ginger (Zingiber officinale), shampoo ginger (Zingiber zerumbet, pink ginger (Alpinia purpurata), and red ginger (Alpinia purpurata). Plant hosts that R. solanacearum infects include: Geranium: Potato: R. solanacearum can overwinter in plant debris or diseased plants, wild hosts, seeds, or vegetative propagative organs like tubers. The bacteria can survive for a long time in water (up to 40 years at 20–25 °C in pure water), and the bacterial population is reduced in extreme conditions (temperature, pH, salts, e.g.). Infected land sometimes cannot be used again for susceptible crops for several years. R. solanacearum can also survive in cool weather and enter a state of being viable but not culturable. In most cases, this stage is not an agricultural threat because the bacteria usually become avirulent after recovering. R. solanacearum causes wilting at high populations (108 – 1010 cfu/g tissue) and disperses in several routes. The large number of R. solanacearum can shed from roots of symptomatic and nonsymptomatic plants. Besides that, bacterial ooze (which is usually used as a sign for detection) on plant surfaces) can enter the surrounding soil or water, contaminating farming equipment or may be acquired by insect vectors. In addition, this pathogen can be spread by contaminated flood water, irrigation, contaminated tools, or infected seeds. In northern Europe, the pathogen has become established in solanaceous weeds which grow in slow-moving rivers. When such contaminated water is used to irrigate potatoes, the pathogen enters the potato production system. Some EU states and Middle Eastern countries have not yet been able to eradicate this pathogen. R. solanacearum usually enters the plant by a wound. Natural wounds (created by excision of flowers, genesis of lateral roots) and unnatural ones (by agricultural practices or nematodes and xylem-feeding bugs attack) could become entry sites for R. solanacearum. The bacteria get access to the wounds partially by flagellar-mediated swimming motility and chemotaxic attraction toward root exudates. Unlike many phytopathogenic bacteria, R. solanacearum potentially requires only one entry site to establish a systemic infection that results in bacterial wilt.