Potato Brown Rot Research Articles

Detection of Ralstonia solanacearum, which causes brown rot of potato, by fluorescent in situ hybridization with 23S rRNA-targeted probes.

During the past few years, Ralstonia (Pseudomonas) solanacearum race 3, biovar 2, was repeatedly found in potatoes in Western Europe. To detect this bacterium in potato tissue samples, we developed a method based on fluorescent in situ hybridization (FISH). The nearly complete genes encoding 23S rRNA of five R. solanacearum strains and one Ralstonia pickettii strain were PCR amplified, sequenced, and analyzed by sequence alignment. This resulted in the construction of an unrooted tree and supported previous conclusions based on 16S rRNA sequence comparison in which R. solanacearum strains are subdivided into two clusters. Based on the alignments, two specific probes, RSOLA and RSOLB, were designed for R. solanacearum and the closely related Ralstonia syzygii and blood disease bacterium. The specificity of the probes was demonstrated by dot blot hybridization with RNA extracted from 88 bacterial strains. Probe RSOLB was successfully applied in FISH detection with pure cultures and potato tissue samples, showing a strong fluorescent signal. Unexpectedly, probe RSOLA gave a less intense signal with target cells. Potato samples are currently screened by indirect immunofluorescence (IIF). By simultaneously applying IIF and the developed specific FISH, two independent targets for identification of R. solanacearum are combined, resulting in a rapid (1-day), accurate identification of the undesired pathogen. The significance of the method was validated by detecting the pathogen in soil and water samples and root tissue of the weed host Solanum dulcamara (bittersweet) in contaminated areas.

Situation of Ralstonia solanacearum in the EPPO region in 1997

In the early 1990s, Ralstonia solanacearum, an EPPO A2 quarantine pest which previously occurred only sporadically in some of the southern Member Countries, caused a number of outbreaks of potato brown rot over a wider area in the EPPO region. The National Plant Protection Organizations of the EPPO Member Countries concerned have taken action to eradicate the pest, and in particular the European Union has taken joint action through a Control Directive. Eradication has been successful in many cases, but is complicated by the fact that R. solanacearum can persist on wild Solanum dulcamara and be dispersed by water. EPPO has collected information from its Member Countries through the period of the outbreaks and eradication, and presents in this article an overall view and a detailed country‐by‐country situation.

Potato brown rot in western Europe – history, present occurrence and some remarks on possible origin, epidemiology and control strategies

Since 1992 an increased number of outbreaks of potato brown rot, caused by the bacterium Ralstonia (Burkholderia, Pseudomonas) solanacearum race 3, biovar 2, has been reported in several EPPO member countries, including more northern states like Belgium, France, The Netherlands and the UK. The largest outbreak took place in The Netherlands in 1995, mainly through one heavily infected seed‐tuber line. The bacterium was found in most infested countries in surface water and in the weed Solanum dulcamara growing along waterways. In some countries, tomato was also found to be infected. The history of the so‐called‘low‐temperature’race 3, adapted to more temperate climates (also occurring at higher altitudes in the tropics) is described, together with details on its host range and geographical distribution. Possible origins of the disease in western Europe are discussed, including introduction through import of infected early ware or industrial potatoes from some countries in the Mediterranean area, where the disease is established. The brown rot bacterium has many similarities concerning its biology and epidemiology with some other infectious diseases, e.g. with cholera, and useful comparisons can be made for control strategies. A detailed account on the epidemiology of P. solanacearum and possible prevention and control strategies is presented. These strategies are: (1) responsibility for prevention and control is for the country where the disease occurs; (2) countries where the disease occurs should report outbreaks as soon as possible; (3) early and sure detection and diagnosis of the pathogen are the core of the system; (4) adequate prevention and control measures should be taken after an outbreak; (5) production of healthy seed tubers should be guaranteed and surveys and (laboratory) checks for (latent) infections performed; (6) education of scientific personnel and the public (farmers, traders, advisory service, etc.) is essential. It is foreseen that hygienic measures and avoidance of surface water for irrigation will be key factors in successful control of the disease.

Survival and possibilities for extinction ofPseudomonas solanacearum (Smith) Smith in cool climates

The importance of biovar 2 ofPseudomonas solanacearum (syn.Burkholderia solanacearum; syn.Ralstonia solanacearum) in cool temperate climates has been recently emphasised by outbreaks of potato brown rot disease in some European countries. Dissemination of the pathogen in latently infected potato tubers and in contaminated irrigation water, and overwintering in aquatic roots of the weed hostSolanum dulcamara have been implicated. Evidence from the literature suggests that in cool climates the organism is unlikely to persist long term in soil in the absence of a susceptible host. Effective control strategies rely on the enforcement of quarantine legislation at both national and European Community levels. This requires knowledge of the biology of the pathogen in cool environments, methods for accurate monitoring of its survival and distribution at and around disease outbreak sites and application of effective measures for pathogen exclusion, containment and eventual eradication. This paper reviews current knowledge on the above.

Corynebacterium sepedonicum . [Descriptions of Fungi and Bacteria

Abstract A description is provided for Corynebacterium sepedonicum . Information is included on the disease caused by the organism, its transmission, geographical distribution, and hosts. HOSTS: On Solanum tuberosum , also on Solanum melongena , other species of Solanum and Lycopersicon esculentum by inoculation (24: 164; 28: 141). DISEASE: Ring rot. A vascular wilt affecting foliage late in the growing season and producing in tubers, a creamy-yellow or light-brown, crumbly rot, which develops in the tissues immediately surrounding the vascular strands, leading usually to the formation of a ring of disorganized tissue or a gap between the cortex and the pith of the tuber. Distinguished from brown rot of potato caused by Pseudomonas solanacearum [Ralstonia solanacearum] (CMI Descript. 15), by differences in tuber symptoms and in staining reactions of the two pathogens (41: 57) p. 69. GEOGRAPHICAL DISTRIBUTION: North America, Europe, doubtful records in Asia (CMI Map 20). TRANSMISSION: By infected tubers, on contaminated cutting knives and bags, and by insects. Where the tuber is cut into seed pieces the risk of spread by the cutting knife is very great.