Invasive Species Compendium

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Datasheet

Ralstonia solanacearum
(bacterial wilt of potato)

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Datasheet

Ralstonia solanacearum (bacterial wilt of potato)

Summary

  • Last modified
  • 27 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Pest
  • Natural Enemy
  • Preferred Scientific Name
  • Ralstonia solanacearum
  • Preferred Common Name
  • bacterial wilt of potato
  • Taxonomic Tree
  • Domain: Bacteria
  •   Phylum: Proteobacteria
  •     Class: Betaproteobacteria
  •       Order: Burkholderiales
  •         Family: Ralstoniaceae
  • Summary of Invasiveness
  • The strains in the race 3 group are a select agent under the US Agricultural Bioterrorism Protection Act of 2002 (USDA, 2005). Peculiarly, the organism, if not yet already pre...

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Pictures

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PictureTitleCaptionCopyright
Left: early wilting symptoms in a potato plant (natural infection).
Right: severe wilting symptoms in potato, caused by R. solanacearum (natural infection).
TitleEarly and severe symptoms in potato
CaptionLeft: early wilting symptoms in a potato plant (natural infection). Right: severe wilting symptoms in potato, caused by R. solanacearum (natural infection).
CopyrightJ.D. Janse
Left: early wilting symptoms in a potato plant (natural infection).
Right: severe wilting symptoms in potato, caused by R. solanacearum (natural infection).
Early and severe symptoms in potatoLeft: early wilting symptoms in a potato plant (natural infection). Right: severe wilting symptoms in potato, caused by R. solanacearum (natural infection).J.D. Janse
Potato plants have wilted and leaves have become brown due to R. solanacearum.
TitleSymptoms on potato plants
CaptionPotato plants have wilted and leaves have become brown due to R. solanacearum.
CopyrightMauritius Sugar Industry Research Institute
Potato plants have wilted and leaves have become brown due to R. solanacearum.
Symptoms on potato plantsPotato plants have wilted and leaves have become brown due to R. solanacearum.Mauritius Sugar Industry Research Institute
Pepper plants show wilting due to bacterial infection.
TitleDamage symptoms on pepper
CaptionPepper plants show wilting due to bacterial infection.
Copyright©CABI BioScience
Pepper plants show wilting due to bacterial infection.
Damage symptoms on pepperPepper plants show wilting due to bacterial infection.©CABI BioScience
Potato tuber infected by R. solanacearum (natural infection) showing droplets of bacterial slime oozing from the eyes and clumps of soil sticking to this slime.
TitleInfected potato tuber
CaptionPotato tuber infected by R. solanacearum (natural infection) showing droplets of bacterial slime oozing from the eyes and clumps of soil sticking to this slime.
CopyrightPlant Protection Service
Potato tuber infected by R. solanacearum (natural infection) showing droplets of bacterial slime oozing from the eyes and clumps of soil sticking to this slime.
Infected potato tuberPotato tuber infected by R. solanacearum (natural infection) showing droplets of bacterial slime oozing from the eyes and clumps of soil sticking to this slime.Plant Protection Service
Left: early symptoms of brown rot in a potato tuber caused by R. solanacearum (natural infection); note vascular browning and drops of bacterial slime.
Right: advanced symptoms of brown rot in a potato tuber (natural infection); note vascular browning and drops of bacterial slime. A blackish soft rot, caused by secondary organisms has already started.
TitleEarly and advanced symptoms on tubers
CaptionLeft: early symptoms of brown rot in a potato tuber caused by R. solanacearum (natural infection); note vascular browning and drops of bacterial slime. Right: advanced symptoms of brown rot in a potato tuber (natural infection); note vascular browning and drops of bacterial slime. A blackish soft rot, caused by secondary organisms has already started.
CopyrightPlant Protection Service
Left: early symptoms of brown rot in a potato tuber caused by R. solanacearum (natural infection); note vascular browning and drops of bacterial slime.
Right: advanced symptoms of brown rot in a potato tuber (natural infection); note vascular browning and drops of bacterial slime. A blackish soft rot, caused by secondary organisms has already started.
Early and advanced symptoms on tubersLeft: early symptoms of brown rot in a potato tuber caused by R. solanacearum (natural infection); note vascular browning and drops of bacterial slime. Right: advanced symptoms of brown rot in a potato tuber (natural infection); note vascular browning and drops of bacterial slime. A blackish soft rot, caused by secondary organisms has already started.Plant Protection Service
Potato stem infected with R. solanacearum (natural infection). Stem has been cut and placed in a beaker of water; threads of bacterial slime ooze out of the vascular bundles.
TitleBacterial slime oozing from vascular bundles
CaptionPotato stem infected with R. solanacearum (natural infection). Stem has been cut and placed in a beaker of water; threads of bacterial slime ooze out of the vascular bundles.
CopyrightPlant Protection Service
Potato stem infected with R. solanacearum (natural infection). Stem has been cut and placed in a beaker of water; threads of bacterial slime ooze out of the vascular bundles.
Bacterial slime oozing from vascular bundlesPotato stem infected with R. solanacearum (natural infection). Stem has been cut and placed in a beaker of water; threads of bacterial slime ooze out of the vascular bundles. Plant Protection Service
Light micrograph of cells of R. solanacearum in and around a spiral vessel of potato. Gram stain.
TitleR. solanacearum cells in potato
CaptionLight micrograph of cells of R. solanacearum in and around a spiral vessel of potato. Gram stain.
CopyrightJ.D. Janse
Light micrograph of cells of R. solanacearum in and around a spiral vessel of potato. Gram stain.
R. solanacearum cells in potatoLight micrograph of cells of R. solanacearum in and around a spiral vessel of potato. Gram stain.J.D. Janse

Identity

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Preferred Scientific Name

  • Ralstonia solanacearum (Smith 1896) Yabuuchi et al. 1996

Preferred Common Name

  • bacterial wilt of potato

Other Scientific Names

  • Bacillus musae Rorer 1911
  • Bacillus musarum Zeman 1921
  • Bacillus nicotianae Uyeda 1904
  • Bacillus sesami Malkoff 1906
  • Bacillus solanacearum Smith 1896
  • Bacterium solanacearum (Smith) Chester 1897
  • Bacterium solanacearum var. asiatica (Smith) Magrou 1937
  • Bacterium solanacearum var. asiaticum Smith 1914
  • Burkholderia solanacearum (Smith 1896) Yabuuchi et al. 1992
  • Chromobacterium nicotianae (Uyeda) Krasil'nikov 1949
  • Erwinia nicotianae (Uyeda) Bergey et al. 1923
  • Erwinia solanacearum (Smith) Holland 1920
  • Phytobacterium solanacearum (Smith) Patel & Kulkarni 1951
  • Phytomonas ricini Archibald 1927
  • Phytomonas solanacearum (Smith) Bergey et al. 1923
  • Phytomonas solanacearum var. asiatica (Smith) Stapp 1928
  • Pseudomonas batatae Cheng & Faan 1962
  • Pseudomonas ricini (Archibald) Robbs 1954
  • Pseudomonas solanacearum (Smith 1896) Smith 1914
  • Pseudomonas solanacearum var. asiatica (Smith) 1928
  • Pseudomonas tectonae Roldan & Andres 1953
  • Xanthomonas solanacearum (Smith) Dowson 1943
  • Xanthomonas solanacearum var. asiatica (Smith) Elliott 1951

International Common Names

  • English: bacterial wilt; bacterial wilt of solanaceous crops; bacterial wilt of teak; brown rot of potato; brown rot of solanaceous crops; granville wilt of tobacco; moko disease: banana; seedling rot; slime disease: potato; southern bacterial blight of tomato
  • Spanish: marchitez bacteriana; marchitez del platano; marchitez del tomate; moco del platano; podredumbre parda de la patata; vaquita de la papa
  • French: bactériose vasculaire; bactériose vasculaire de la pomme de terre; flétrissement bactérien de la pomme de terre; flétrissement bactérien de la pomme de terre; flétrissement bactérien de la tomate; flétrissement bactérien des solanacées; flétrissement bactérien du bananier; flétrissement bactérien du tabac; maladie de moko du bananier; pourriture brune

Local Common Names

  • Germany: Bakterienwelke; Braunfäule der Kartoffel; Schleimkrankheit

Summary of Invasiveness

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The strains in the race 3 group are a select agent under the US Agricultural Bioterrorism Protection Act of 2002 (USDA, 2005). Peculiarly, the organism, if not yet already present in North America in pelargonium (Strider et al., 1981), was introduced with cuttings of this host by American companies producing these cuttings for their markets in countries like Kenya and Guatamala (Norman et al., 1999, 2009; Kim et al., 2002; Williamson et al., 2002; Williamson et al., 2002; O’Hern, 2004). A similar situation led to introductions of the pathogen from Kenya into some northern European nurseries. Once the source (contaminated surface water) was recognized and proper control measures (use of deep soil water, disinfection of cutting producing premises and replacement of mother stock), the problem was solved and the disease in greenhouses eradicated (Janse et al., 2004); Similarly race 1 has been introduced into greenhouses with ornamental plants (rhizomes, cuttings or fully grown plants) such as Epipremnum, Anthurium, Curcuma spp. and Begonia eliator from tropical areas (Norman and Yuen, 1998, 1999; Janse et al., 2006; Janse, 2012). Introduction can and did occur from Costa Rica and the Caribbean, Indonesia, Thailand and South Africa. However, this idea of placing pathogens on bioterrorist list for unclear and perhaps industry-driven reasons and its effects, is strongly opposed in a recent publication from leading phytobacteriologists. This is because R. solanacearum is an endemic pathogen, causing endemic disease in most parts of its geographic occurrence, moreover normal quarantine regulations are already in place where the disease is not present or only sporadically and are thought to be more efficient and less damaging to trade and research than placing this pathogen on select agent lists and treating it as such (Young et al., 2008). Peculiarly, it has been used in the control of a real invasive species, the weed kahili ginger (Hedychium gardenarium) in tropical forests in Hawaii. This is not without risks because strains occurring on this weed host were thought to be non-virulent, but later appeared to be virulent on many edible and ornamental ginger species as well (Anderson and Gardner, 1999; Paret et al., 2008). The earlier mentioned tropical strains belonging to phylotype II/4 NPB could become an emerging problem not only in the Caribbean, but also to Southern Europe and North Africa where higher yearly temperatures prevail. Another threat for these countries could be strains belonging to race 1, biovar 1 (phylotype I) that have already been reported from field-grown potatoes in Portugal (Cruz et al., 2008).

 

Taxonomic Tree

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  • Domain: Bacteria
  •     Phylum: Proteobacteria
  •         Class: Betaproteobacteria
  •             Order: Burkholderiales
  •                 Family: Ralstoniaceae
  •                     Genus: Ralstonia
  •                         Species: Ralstonia solanacearum

Notes on Taxonomy and Nomenclature

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Ralstonia solanacearum was originally included in the Approved Lists (Skerman et al., 1980) as Pseudomonas solanacearum, the name already given by Erwin Smith in 1914. In a comparative study of non-fluorescent species of the genus Pseudomonas, Yabuuchi et al. (1992) proposed the transfer of P. solanacearum and related non-fluorescent pseudomonads to a novel genus, Burkholderia. A subsequent study of this genus a few years later indicated that B. solanacearum was sufficiently distinct from other members of the genus to warrant assignment to the newly proposed genus, Ralstonia (Yabuuchi et al., 1995) with the closely related plant pathogenic species, Ralstonia syzygii, causal agent of Sumatra disease of clove tree (Syzygium aromaticum) and the distinct Blood Disease Bacterium, causal agent of blood disease of banana, in Indonesia (now classified as Ralstonia haywardii subspecies celebensis, see below).

R. solanacearum comprises sub-populations variously reported as groups, races, biovars, biotypes, sub-races and strains. The commonly applied terms biovar and biotype refer to differences in biochemical and phage reactions (Hayward, 1962). Races, distinguished on the basis of differences in plant host range (Buddenhagen et al., 1962), are usually referred to in this text.

At the end of the nineteenth century a severe wilting disease (called 'slime disease') was described in (sub)tropical regions on tomato, tobacco, potato, banana and peanut. The founder of phytobacteriology, the American Erwin F. Smith, had already proved in 1896 that the causal organism was a bacterium (named by him as Bacillus solanacearum). In 1914 Smith placed this non-spore forming, Gram-negative bacterium in the genus Pseudomonas. In the following years 'slime disease' proved to be present in many different hosts in (sub)tropical regions. However, Moraes (1947) described a variant of the bacterium in Portugal that was better adapted to temperate climatic regions (growth optimum of 27 instead of 35ºC). This variant was also found later in other Mediterranean countries, especially Egypt, and in mountainous areas in the tropics (Janse, 1996). This 'cold' variant and the variant on banana could be easily discriminated on the basis of pathogenicity to different hosts (classification into races) and the use of carbon sources in the laboratory (biochemical varieties or biovars). The tropical variant with a very broad host range was classified by Buddenhagen (1962) as race 1 (from which later Race 4 and 5 were separated), the variant specialised on banana and the related Heliconia species, Race 2, and the 'cold' variant with a restricted host range, mainly Solanaceae, race 3. The 'cold' variant (race 3) appeared to belong to biovar 2 (later also named 2A) in the biochemical classification of Hayward (see Hayward, 1994), whereas the other races contained biovars 1 and 3-5. A special biovar (2T or 2N) of race 3 occurs in the Andes, and in this area resistance against race 3 was also found in wild potato. Moreover, once studied, strains from highland cultivation of potato and tomato in South and North America are usually Race 3, biovar 2 = Phylotype IIB sequevar 1, see below (Janse, 1996; Janse et al., 2004; Sanchez-Perez, 2008; Siri et al., 2011). This led to the presumption that Race 3, biovar 2 has spread from the Andes region with potato, perhaps especially during the second World War with allied troops, to the Mediterranean area (Janse, 1996; Cellier and Prior, 2010; Wicker et al., 2011). Race 3, biovar 2 appears to be genetically very homogeneous. In a comparative study of non-fluorescent species of the genus Pseudomonas, Yabuuchi et al. (1992) proposed the transfer of P. solanacearum and related non-fluorescent pseudomonads to a novel genus, Burkholderia. A subsequent study of this genus a few years later indicated that B. solanacearum was sufficiently distinct from other members of the genus to warrant assignment to the newly proposed genus, Ralstonia (Yabuuchi et al., 1995) with the closely related plant pathogenic species, R. syzygii, causal agent of Sumatra disease of clove tree (Syzygium aromaticum), and the distinct Blood Disease Bacterium, causal agent of blood disease of banana, in Indonesia. Further molecular-biological/taxonomic investigations have enabled a more refined classification of Rsol, e.g., on the basis of Restriction Fragment Length Polymorphism (RFLP)- and 16S rRNA-analysis and sequence-analysis of the endonuclease (egl) gene and other so-called household genes (Cook and Sequeira, 1994; van der Wolf et al., 1998; Saddler et al., 1998; Poussier et al., 2000; Timms et al., 2001; Fegan and Prior, 2005; Gabriel et al., 2006; Castillo and Greenberg, 2007; Pinghsheng et al., 2007). On the basis of sequence analysis, four so-called phylotypes are discriminated: Phylotype I contains strains from Asia, phylotype II from the American continent (IIB holds the Race 3, biovar 2 strains (sequevar 1), IIa other strains, e.g., from Musa and tomato, also some from Africa), phylotype III (holds biovars 1 and 2T from Africa, and phylotype IV (holds biovars 1, 2 and 2T and also the closely related R. syzygii and the blood disease bacterium (BDB). Strains of this phylotype originate from Indonesia, Japan and Australia (Fegan and Prior, 2005, 2006; Wicker et al., 2007, 2009, 2011). A new, aggressive variant (phylotype II/4NPB = non-pathogenic to banana) with many hosts, including Anthurium, Cucurbitaceae and tomato, was recently described from Martinique (Wicker et al., 2007, 2009). This phylotype could be a threat for European greenhouse cultivation and was already reported from France (Cellier and Prior 2010). The 'cold' form (Race 3, biovar 2 or R3b2) that occurred/occurs in many European countries (Janse, 1996; EPPO PQR database) is in the recent typing studies genetically very homogenous and has always been classified until now as Ralstonia solanacearum (Rsol) R3b2, phylotype IIB (sequevar 1 and 2). This homogeneity was recently also confirmed from China (Xu et al., 2009; Xue et al., 2011).

In a recent whole genome sequencing taxonomic study by Remenant et al. (2011), the following important taxonomic and nomenclatorial changes have been proposed:

Phylotypes I and III strains appear to form a unique genomic species, for which the name Ralstonia sequeirae is proposed, with type strain GM I1000;

Phylotype II strains, including the original Rsol type strain K60T, are maintained asR. solanacearum;

Phylotype IV strains, including those of R. syzygii and the BLDB strains also form a genomic species, for which R. haywardii, with type strain PSI07, where the broad host range strains are designated R. haywardii subspecies solanacearum with type strain PSI07, the BLDB strains as R. haywardii subspecies celebensis with type strain R229 and the R. syzygii that are insect-transmitted by tube-building Hindola spp. cercopoids, as R. haywardii subspeciessyzygii.

The complete genome of the following strains has been sequenced (December 2011): CFBP2957 (tomato, phylotype IIA), CMR15 (tomato, phylotype III) and PSI07 (tomato, phylotype IV); GMI1000 (tomato, phylotype I); IPO1609 (potato, phylotype IIB); and Molk2 (banana, phylotype IIB) (see Remenant et al., 2010). Po82 (pathogenic to Musa and solanaceous plants, phylotype IIB/sequevar 4 (Xu et al., 2011)); Strain Y45 (Nicotiana tabacum, phyllotype I, Li et al. (2011).

Description

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R. solanacearum is a Gram-negative bacterium with rod-shaped cells, 0.5-1.5 µm in length, with a single, polar flagellum. The positive staining reaction for poly-ß-hydroxybutyrate granules with Sudan Black B or Nile Blue distinguishes R. solanacearum from many other (phytopathogenic) Gram-negative bacterial species. Gram-negative rods with a polar tuft of flagella, non-fluorescent but diffusible brown pigment often produced. Polyhydroxybutyrate (PHB) is accumulated as cellular reserve and can be detected by Sudan Black staining on nutrient-rich media or the Nile Blue test, also in smears from infected tissues (Anonymous, 1998; 2006) On the general nutrient media, virulent isolates of R. solanacearum develop pearly cream-white, flat, irregular and fluidal colonies often with characteristic whorls in the centre. Avirulent forms of R. solanacearum form small, round, non-fluidal, butyrous colonies which are entirely cream-white. On Kelman’s tetrazolium and SMSA media, the whorls are blood red in colour. Avirulent forms of R. solanacearum form small, round, non-fluidal, butyrous colonies which are entirely deep red.

Distribution

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R. solanacearum is widespread in tropical, subtropical and warm temperate areas throughout the world. Its occurrence has also been reported from temperate zones. In particular, race 3 which was described by Moraes in 1947 from Portugal, was first found to spread in the Mediterranean basin, whereafter further spread took place with importation of infected early potatoes from that area, where brown rot was causing problems, most notably in Egypt. Further spread occurred through irrigation, especially in the 1980s and 1990s when irrigation in potato in northern Europe became more common to raise production and the possibility of controlling potato scab (Janse, 1996, 2012).

Many older host records (of Pseudomonas solanacearum) were made without deposition of host reference strains and these cannot now be allocated to a particular race. It will only be possible to make allocations when further isolates from hosts are obtained and characterized.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Asia

ArmeniaAbsent, invalid recordEPPO, 2014
BangladeshWidespreadCABI/EPPO, 1999; EPPO, 2014
BhutanPresentEPPO, 2005; EPPO, 2014
Brunei DarussalamPresentEPPO, 2005; EPPO, 2014
CambodiaAbsent, unreliable recordEPPO, 2014
ChinaRestricted distributionCABI/EPPO, 1999
-AnhuiPresentCABI/EPPO, 1999; EPPO, 2014
-ChongqingPresentYin et al., 2006
-FujianPresentCABI/EPPO, 1999; EPPO, 2014
-GuangdongWidespreadCABI/EPPO, 1999; EPPO, 2014
-GuangxiPresentCABI/EPPO, 1999; EPPO, 2014
-GuizhouPresentLong et al., 2008
-HainanPresentTan et al., 2006
-HebeiPresentCABI/EPPO, 1999; EPPO, 2014
-HenanPresentCABI/EPPO, 1999; EPPO, 2014
-Hong KongPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
-HubeiPresentCABI/EPPO, 1999; EPPO, 2014
-HunanPresentCABI/EPPO, 1999; EPPO, 2014
-JiangsuPresentCABI/EPPO, 1999; EPPO, 2014
-JiangxiPresentCABI/EPPO, 1999; EPPO, 2014
-ShandongPresentCABI/EPPO, 1999; EPPO, 2014
-SichuanPresentCABI/EPPO, 1999; EPPO, 2014
-YunnanPresentCABI/EPPO, 1999; Li et al., 2012; EPPO, 2014
-ZhejiangPresentCABI/EPPO, 1999; EPPO, 2014
Georgia (Republic of)Restricted distributionCABI/EPPO, 1999; Mepharishvili et al., 2012; EPPO, 2014
IndiaWidespreadCABI/EPPO, 1999; EPPO, 2014
-Andaman and Nicobar IslandsPresentEPPO, 2005; EPPO, 2014
-Andhra PradeshPresentCABI/EPPO, 1999; EPPO, 2014
-AssamPresentCABI/EPPO, 1999; EPPO, 2014
-BiharPresent
-Himachal PradeshPresentCABI/EPPO, 1999; EPPO, 2014
-Indian PunjabPresentCABI/EPPO, 1999; EPPO, 2014
-JharkhandPresentDubey, 2005
-KarnatakaPresentCABI/EPPO, 1999; EPPO, 2014
-KeralaPresentCABI/EPPO, 1999; EPPO, 2014
-Madhya PradeshPresentCABI/EPPO, 1999; EPPO, 2014
-MaharashtraPresentCABI/EPPO, 1999; EPPO, 2014
-ManipurPresentCABI/EPPO, 1999; EPPO, 2014
-MeghalayaPresentCABI/EPPO, 1999; EPPO, 2014
-NagalandPresentCABI/EPPO, 1999; EPPO, 2014
-OdishaPresentCABI/EPPO, 1999; EPPO, 2014
-Tamil NaduPresentCABI/EPPO, 1999; EPPO, 2014
-TripuraPresentCABI/EPPO, 1999; EPPO, 2014
-Uttar PradeshPresentCABI/EPPO, 1999; EPPO, 2014
-UttarakhandPresentSunaina and Tomar, 2003
-West BengalPresentCABI/EPPO, 1999; Mondal et al., 2012; EPPO, 2014; Sarkar and Chaudhuri, 2015
IndonesiaPresentCABI/EPPO, 1999; EPPO, 2014
-Irian JayaPresentCABI/EPPO, 1999; EPPO, 2014
-JavaPresentCABI/EPPO, 1999; EPPO, 2014
-SulawesiPresentCABI/EPPO, 1999; EPPO, 2014
-SumatraPresentCABI/EPPO, 1999; EPPO, 2014
IranPresentCABI/EPPO, 1999; EPPO, 2014
IsraelEradicatedIntroduced1970sCABI/EPPO, 1999
JapanRestricted distributionCABI/EPPO, 1999; EPPO, 2014
-HonshuPresentCABI/EPPO, 1999; EPPO, 2014
-KyushuPresentCABI/EPPO, 1999; EPPO, 2014
Korea, DPRPresentCABI/EPPO, 1999; EPPO, 2014
Korea, Republic ofPresentCABI/EPPO, 1999; EPPO, 2014
LebanonPresentCABI/EPPO, 1999; EPPO, 2014
MalaysiaWidespreadCABI/EPPO, 1999; EPPO, 2014
-Peninsular MalaysiaPresentEPPO, 2005; EPPO, 2014
-SabahPresentCABI/EPPO, 1999; EPPO, 2014
-SarawakPresentCABI/EPPO, 1999; EPPO, 2014
MyanmarPresentCABI/EPPO, 1999; EPPO, 2014
NepalPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
PakistanPresentCABI/EPPO, 1999; EPPO, 2014
PhilippinesPresentCABI/EPPO, 1999; EPPO, 2014
Saudi ArabiaPresentEPPO, 2005; EPPO, 2014
SingaporePresentCABI/EPPO, 1999; race 1; Yik, 1988; Yik et al., 1994; EPPO, 2014
Sri LankaRestricted distributionCABI/EPPO, 1999; EPPO, 2014
TaiwanWidespreadCABI/EPPO, 1999; Wu et al., 2013; EPPO, 2014
ThailandPresentCABI/EPPO, 1999; EPPO, 2014
TurkeyPresentCABI/EPPO, 1999; IPPC, 2007; EPPO, 2014
VietnamPresentCABI/EPPO, 1999; EPPO, 2014

Africa

AlgeriaAbsent, formerly presentEPPO, 2014
AngolaPresentCABI/EPPO, 1999; EPPO, 2014
BeninPresentSikirou et al., 2009; EPPO, 2014; Sikirou et al., 2015
Burkina FasoPresentEPPO, 2014
BurundiPresentCABI/EPPO, 1999; EPPO, 2014
CameroonWidespreadToukam et al., 2009; EPPO, 2014
CongoPresentEPPO, 2014
Congo Democratic RepublicPresentCABI/EPPO, 1999; EPPO, 2014
Côte d'IvoirePresentEPPO, 2014
EgyptPresentCABI/EPPO, 1999; EPPO, 2014
EthiopiaPresentCABI/EPPO, 1999; EPPO, 2014
GabonAbsent, unreliable recordEPPO, 2014
GambiaPresentCABI/EPPO, 1999; EPPO, 2014
GhanaPresentSubedi et al., 2014
KenyaPresentCABI/EPPO, 1999; EPPO, 2014
LesothoPresentEPPO, 2014
LibyaPresentCABI/EPPO, 1999; EPPO, 2014
MadagascarPresentCABI/EPPO, 1999; EPPO, 2014
MalawiWidespreadEPPO, 2014
MaliWidespreadThera et al., 2010; EPPO, 2014
MauritiusPresentCABI/EPPO, 1999; EPPO, 2014
MoroccoPresentCABI/EPPO, 1999; EPPO, 2014
MozambiqueAbsent, unreliable recordEPPO, 2014
NigeriaPresentCABI/EPPO, 1999; EPPO, 2014
RéunionPresentCABI/EPPO, 1999; EPPO, 2014
RwandaPresentCABI/EPPO, 1999; EPPO, 2014
SenegalPresentCABI/EPPO, 1999; EPPO, 2014
SeychellesAbsent, unreliable recordEPPO, 2014
Sierra LeonePresentCABI/EPPO, 1999; EPPO, 2014
SomaliaPresentCABI/EPPO, 1999; EPPO, 2014
South AfricaRestricted distributionCABI/EPPO, 1999; EPPO, 2014
SwazilandPresentEPPO, 2014
TanzaniaPresentCABI/EPPO, 1999; EPPO, 2014
UgandaPresentCABI/EPPO, 1999; EPPO, 2014
ZambiaPresentCABI/EPPO, 1999; EPPO, 2014
ZimbabweRestricted distributionCABI/EPPO, 1999; EPPO, 2014

North America

CanadaAbsent, formerly presentEPPO, 2014
-OntarioAbsent, formerly presentEPPO, 2014
MexicoRestricted distributionCABI/EPPO, 1999; EPPO, 2014
USAWidespreadCABI/EPPO, 1999; EPPO, 2014
-AlabamaPresentCABI/EPPO, 1999; EPPO, 2014
-ArkansasPresentEPPO, 2014
-DelawarePresentKim et al., 2003
-FloridaPresentCABI/EPPO, 1999; EPPO, 2014
-GeorgiaPresentCABI/EPPO, 1999; EPPO, 2014
-HawaiiPresentCABI/EPPO, 1999; EPPO, 2014
-IllinoisPresentEPPO, 2014
-IndianaPresentEPPO, 2014
-MichiganPresentEPPO, 2014
-New HampshirePresentEPPO, 2014
-New JerseyPresentEPPO, 2014
-New YorkEradicated
-North CarolinaPresentCABI/EPPO, 1999; EPPO, 2014
-PennsylvaniaRestricted distributionKim et al., 2003; EPPO, 2014
-South CarolinaPresentRobertson et al., 2004
-South DakotaPresentEPPO, 2014
-WisconsinPresentEPPO, 2014

Central America and Caribbean

BelizeWidespreadCABI/EPPO, 1999; EPPO, 2014
Costa RicaPresentCABI/EPPO, 1999; EPPO, 2014
CubaPresentCABI/EPPO, 1999; EPPO, 2014
DominicaAbsent, unreliable recordEPPO, 2014
Dominican RepublicPresentCABI/EPPO, 1999; EPPO, 2014
El SalvadorPresentCABI/EPPO, 1999; EPPO, 2014
GrenadaPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
GuadeloupePresentCABI/EPPO, 1999; EPPO, 2014
GuatemalaPresentCABI/EPPO, 1999; EPPO, 2014
HaitiAbsent, unreliable recordEPPO, 2014
HondurasPresentCABI/EPPO, 1999; EPPO, 2014
JamaicaAbsent, unreliable recordCABI/EPPO, 1999; IPPC, 2006; EPPO, 2014
MartiniqueWidespreadCABI/EPPO, 1999; EPPO, 2014
NicaraguaPresentCABI/EPPO, 1999; EPPO, 2014
PanamaPresentCABI/EPPO, 1999; EPPO, 2014
Puerto RicoPresentRomero et al., 2013; EPPO, 2014Biovar 1.
Saint LuciaAbsent, unreliable recordEPPO, 2014
Saint Vincent and the GrenadinesWidespreadIPPC, 2007; EPPO, 2014
Trinidad and TobagoWidespreadCABI/EPPO, 1999; EPPO, 2014

South America

ArgentinaAbsent, invalid recordCABI/EPPO, 1999; EPPO, 2014
BoliviaPresentCABI/EPPO, 1999; EPPO, 2014
BrazilPresentCABI/EPPO, 1999; EPPO, 2014
-AlagoasPresentAndrade et al., 2009
-AmapaPresentEPPO, 2014
-AmazonasPresentCABI/EPPO, 1999; EPPO, 2014
-BahiaPresentCABI/EPPO, 1999; EPPO, 2014
-CearaPresentFreire and Mosca, 2009
-Espirito SantoPresentAlfenas et al., 2006; EPPO, 2014
-GoiasPresentCABI/EPPO, 1999; EPPO, 2014
-MaranhaoPresentEPPO, 2014
-Minas GeraisPresentEPPO, 2014; Tebaldi et al., 2014
-ParaPresentEPPO, 2014
-ParanaPresentCABI/EPPO, 1999; EPPO, 2014
-PernambucoPresentCABI/EPPO, 1999; EPPO, 2014
-Rio de JaneiroPresentEPPO, 2014
-Rio Grande do SulPresentCABI/EPPO, 1999; EPPO, 2014
-Santa CatarinaPresentCABI/EPPO, 1999; EPPO, 2014
-Sao PauloPresentCABI/EPPO, 1999; EPPO, 2014
ChileRestricted distributionCABI/EPPO, 1999; EPPO, 2014
ColombiaPresentCABI/EPPO, 1999; EPPO, 2014
EcuadorRestricted distributionCABI/EPPO, 1999; EPPO, 2014
French GuianaPresentEPPO, 2014
GuyanaPresentCABI/EPPO, 1999; EPPO, 2014
ParaguayRestricted distributionEPPO, 2014; Santiago et al., 2014
PeruPresentCABI/EPPO, 1999; EPPO, 2014
SurinamePresentCABI/EPPO, 1999; EPPO, 2014
VenezuelaPresentCABI/EPPO, 1999; EPPO, 2014

Europe

AustriaPresent, few occurrencesEPPO, 2014
BelgiumPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
BulgariaAbsent, formerly presentEPPO, 2014
Czech RepublicTransient: actionable, under eradicationEPPO, 2014
DenmarkAbsent, intercepted onlyIPPC, 2013; EPPO, 2014
FinlandAbsent, confirmed by surveyEPPO, 2014
FrancePresent, few occurrencesEPPO, 2014
GermanyPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
GreecePresent, few occurrencesEPPO, 2014
HungaryPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
ItalyEradicatedEPPO, 2014
-SardiniaEradicatedLoreti et al., 2008; EPPO, 2014
LatviaAbsent, confirmed by surveyEPPO, 2014
LithuaniaAbsent, confirmed by surveyIPPC, 2016
MaltaAbsent, confirmed by surveyEPPO, 2014
MoldovaPresentCABI/EPPO, 1999; EPPO, 2014
NetherlandsRestricted distributionIntroduced1992CABI/EPPO, 1999; EPPO, 2014
PolandTransient: actionable, under eradicationEPPO, 2014
PortugalPresentCruz et al., 2008; EPPO, 2014
-MadeiraEradicatedCABI/EPPO, 1999
RomaniaPresent, few occurrencesEPPO, 2014
Russian FederationRestricted distributionCABI/EPPO, 1999; EPPO, 2014
-Eastern SiberiaAbsent, unreliable recordEPPO, 2014
-Russian Far EastRestricted distributionCABI/EPPO, 2002; EPPO, 2014
-Southern RussiaRestricted distributionCABI/EPPO, 1999; EPPO, 2014
SerbiaPresentMilijasevic-Marcic et al., 2013
SlovakiaPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
SloveniaPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
SpainAbsent, confirmed by surveyCaruso et al., 2005; EPPO, 2014
SwedenPresent, few occurrencesCABI/EPPO, 1999; EPPO, 2014
UKTransient: actionable, under eradicationIPPC, 2010; EPPO, 2014
-England and WalesPresent, few occurrencesCABI/EPPO, 1999
UkrainePresentCABI/EPPO, 1999; EPPO, 2014
Yugoslavia (Serbia and Montenegro)PresentCABI/EPPO, 1999

Oceania

American SamoaAbsent, unreliable recordEPPO, 2014
AustraliaRestricted distributionCABI/EPPO, 1999; EPPO, 2014
-Australian Northern TerritoryPresentCABI/EPPO, 1999; EPPO, 2014
-New South WalesPresentCABI/EPPO, 1999; EPPO, 2014
-QueenslandPresentCABI/EPPO, 1999; EPPO, 2014
-South AustraliaPresentCABI/EPPO, 1999; EPPO, 2014
-VictoriaPresentCABI/EPPO, 1999; EPPO, 2014
-Western AustraliaPresentCABI/EPPO, 1999; EPPO, 2014
Cook IslandsPresentEPPO, 2005; EPPO, 2014
FijiPresentCABI/EPPO, 1999; EPPO, 2014
French PolynesiaPresentEPPO, 2005; EPPO, 2014
GuamPresentEPPO, 2005; EPPO, 2014
Micronesia, Federated states ofPresentEPPO, 2005; EPPO, 2014
New CaledoniaRestricted distributionEPPO, 2005; EPPO, 2014
New ZealandWidespreadEPPO, 2005; EPPO, 2014
Papua New GuineaPresentCABI/EPPO, 1999; EPPO, 2014
SamoaPresentEPPO, 2005; EPPO, 2014
TongaPresentEPPO, 2005; EPPO, 2014
VanuatuPresentEPPO, 2005; EPPO, 2014

Risk of Introduction

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Risk Criteria Category

Economic Importance: High
Distribution: Worldwide
Seedborne Incidence: Moderate
Seed Transmitted: Yes (in some species, e.g. groundnut)
Seed Treatment: Yes

Notes on Phytosanitary Risk

R. solanacearum is an EPPO A2 quarantine organism (OEPP/EPPO, 1978) and is listed by APPPC and IAPSC. The occurrence of different races and strains of the pathogen with varying virulence under different environmental conditions presents a serious danger to European and Mediterranean potato and tomato production. Absence of the bacterium is an important consideration for countries exporting seed potatoes. Hosts other than potato are most likely to be affected in the warmer parts of the EPPO region, where the bacterium already occurs. However, even in these areas, races other than race 3 have not been positively identified, and the introduction of races not occurring in the region could have a great economic impact. For example, banana strains are not found in the banana-producing areas of the southern Mediterranean zone, and virtually have A1 quarantine status. Race 3 (biovar 2) appears to present the most important risk for the EPPO region as a whole because it may be introduced and spread in infected early ware potatoes or seed potatoes. The importation of infected potatoes for cattle fodder or for food or industrial processing may result in the escape of the pathogen. Race 1 strains introduced with planting material may also result in losses if restrictive and severe quarantine measures are applied, for example, in greenhouse production in cooler climates when the pathogen is introduced with planting material, e.g. Curcuma rhizomes (Tuin et al., 1996).

Habitat List

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CategorySub-CategoryHabitatPresenceStatus
Other
Host Present, no further details Harmful (pest or invasive)
Soil Present, no further details Harmful (pest or invasive)
Vector Present, no further details Harmful (pest or invasive)
Host Present, no further details Natural
Soil Present, no further details Natural
Vector Present, no further details Natural
Host Present, no further details Productive/non-natural
Soil Present, no further details Productive/non-natural
Terrestrial
Terrestrial – ManagedCultivated / agricultural land Present, no further details Harmful (pest or invasive)
Cultivated / agricultural land Present, no further details Natural
Cultivated / agricultural land Present, no further details Productive/non-natural
Protected agriculture (e.g. glasshouse production) Present, no further details Harmful (pest or invasive)
Protected agriculture (e.g. glasshouse production) Present, no further details Productive/non-natural
Managed forests, plantations and orchards Present, no further details Harmful (pest or invasive)
Managed forests, plantations and orchards Present, no further details Natural
Managed forests, plantations and orchards Present, no further details Productive/non-natural
Rail / roadsides Present, no further details
Urban / peri-urban areas Present, no further details
Terrestrial ‑ Natural / Semi-naturalNatural forests Present, no further details Harmful (pest or invasive)
Natural forests Present, no further details Natural
Natural forests Present, no further details Productive/non-natural
Riverbanks Present, no further details Harmful (pest or invasive)
Riverbanks Present, no further details Natural
Riverbanks Present, no further details Productive/non-natural
Wetlands Present, no further details Harmful (pest or invasive)
Wetlands Present, no further details Productive/non-natural
Littoral
Coastal areas Present, no further details Harmful (pest or invasive)
Coastal areas Present, no further details Natural
Coastal areas Present, no further details Productive/non-natural
Freshwater
Irrigation channels Present, no further details Harmful (pest or invasive)
Irrigation channels Present, no further details Natural
Irrigation channels Present, no further details Productive/non-natural
Lakes Present, no further details Harmful (pest or invasive)
Lakes Present, no further details Natural
Rivers / streams Present, no further details Harmful (pest or invasive)
Rivers / streams Present, no further details Productive/non-natural
Ponds Present, no further details Harmful (pest or invasive)
Ponds Present, no further details Productive/non-natural

Hosts/Species Affected

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R. solanacearum as a species has an extremely wide host range, but different pathogenic varieties (races) within the species may show more restricted host ranges. Over 200 species, especially tropical and subtropical crops, are susceptible to one or other of the races of R. solanacearum. Worldwide, the most important are: tomato, tobacco, aubergine, potato, banana, plantain and Heliconia. Within the EPPO region, race 3 (see Biology and Ecology) with a limited host range including potato, tomato and the weed Solanum dulcamara, is considered to have potential for spread.

Other host crops are: Anthurium spp., groundnut, Capsicum annuum, cotton, rubber, sweet potato, cassava, castor bean and ginger.

Many weeds are alternative hosts of the pathogen. Solanum cinereum in Australia (Graham and Lloyd, 1978), Solanum nigrum and, in rare cases, Galinsoga parviflora, G. ciliata, Polygonum capitata, Portulaca oleracea (for example, in Nepal; Pradhanang and Elphinstone, 1996a) and Urtica dioica have been reported as weed hosts for race 3 (Wenneker et al., 1998). S. nigrum and S. dulcamara are primary wild hosts for race 3.

Lists of host records have been recorded (Kelman, 1953; Bradbury, 1986; Persley, 1986; Hayward, 1994a) but the original reports, gathered over many years, vary greatly in reliability. Few reference strains from reported host plants have been deposited in publicly accessible culture collections to support the authenticity of records.

Host Plants and Other Plants Affected

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Plant nameFamilyContext
Ageratum conyzoides (billy goat weed)AsteraceaeWild host
Amomum subulatum (large cardamom)ZingiberaceaeOther
Annona cherimola (cherimoya)AnnonaceaeMain
AnthuriumAraceaeOther
Arachis hypogaea (groundnut)FabaceaeMain
Artemisia (wormwoods)AsteraceaeOther
Beta vulgaris (beetroot)ChenopodiaceaeOther
Beta vulgaris var. ciclaChenopodiaceaeOther
Bougainvillea glabraNyctaginaceaeOther
Capsicum annuum (bell pepper)SolanaceaeOther
Casuarina cunninghamiana (Australian beefwood)CasuarinaceaeMain
Casuarina equisetifolia (casuarina)CasuarinaceaeMain
Casuarina glauca (scaly oak (Australia))CasuarinaceaeMain
Cereus peruvianusCactaceaeOther
Cestrum nocturnum (night jessamine)SolanaceaeOther
Chenopodium (Goosefoot)ChenopodiaceaeOther
Citrullus lanatus (watermelon)CucurbitaceaeOther
ColeusLamiaceaeOther
Coleus forskohliiLamiaceaeOther
Colocasia esculenta (taro)AraceaeOther
Corchorus olitorius (jute)TiliaceaeOther
Cosmos bipinnatus (garden cosmos)AsteraceaeOther
Cucumis melo (melon)CucurbitaceaeOther
Cucumis sativus (cucumber)CucurbitaceaeOther
Cucurbita moschata (pumpkin)CucurbitaceaeOther
Cucurbita pepo (marrow)CucurbitaceaeOther
Curcuma longa (turmeric)ZingiberaceaeOther
Cynara cardunculus var. scolymus (globe artichoke)AsteraceaeOther
Cyphomandra betacea (tree tomato)SolanaceaeOther
Datura stramonium (jimsonweed)SolanaceaeOther
Emilia sonchifolia (red tasselflower)AsteraceaeOther
EucalyptusMyrtaceaeOther
Eupatorium cannabinumAsteraceaeOther
Galinsoga parviflora (gallant soldier)AsteraceaeWild host
Galinsoga quadriradiata (shaggy soldier)AsteraceaeWild host
Gossypium (cotton)MalvaceaeOther
HeliconiaHeliconiaceaeMain
Heliconia caribaeaHeliconiaceaeOther
Hevea brasiliensis (rubber)EuphorbiaceaeOther
Ipomoea batatas (sweet potato)ConvolvulaceaeOther
Justicia adhatoda (Malabar nut)AcanthaceaeOther
Lagenaria siceraria (bottle gourd)CucurbitaceaeOther
Maranta arundinacea (West Indian arrowroot)MarantaceaeOther
Momordica charantia (bitter gourd)CucurbitaceaeOther
Musa (banana)MusaceaeMain
Musa x paradisiaca (plantain)MusaceaeMain
Nicotiana rustica (wild tobacco)SolanaceaeOther
Nicotiana tabacum (tobacco)SolanaceaeMain
Olea europaea subsp. europaea (European olive)OleaceaeOther
Pelargonium (pelargoniums)GeraniaceaeOther
Pelargonium hortorumGeraniaceaeOther
Pelargonium zonale hybridsGeraniaceaeOther
Physalis (Groundcherry)SolanaceaeOther
Physalis angulata (cutleaf groundcherry)SolanaceaeOther
Platostoma chinensisLamiaceaeOther
Plectranthus barbatusLamiaceaeOther
Pogostemon cablin (patchouli)LamiaceaeOther
Polygonum capitatum (pinkhead smartweed)PolygonaceaeWild host
Portulaca oleracea (purslane)PortulacaceaeWild host
Ricinus communis (castor bean)EuphorbiaceaeOther
Rosa (roses)RosaceaeOther
Salpiglossis sinuataSolanaceaeOther
Salvia reflexaLamiaceaeOther
Siraitia grosvenoriiCucurbitaceaeOther
Solanum capsicastrumSolanaceaeOther
Solanum carolinense (horsenettle)SolanaceaeOther
Solanum cinereumSolanaceaeWild host
Solanum dulcamara (bittersweet nightshade)SolanaceaeOther
Solanum luteumSolanaceaeOther
Solanum lycopersicum (tomato)SolanaceaeMain
Solanum melongena (aubergine)SolanaceaeMain
Solanum nigrum (black nightshade)SolanaceaeWild host
Solanum phurejaSolanaceaeOther
Solanum sisymbriifoliumSolanaceaeOther
Solanum tuberosum (potato)SolanaceaeMain
Soliva anthemifoliaAsteraceaeOther
Tagetes (marigold)AsteraceaeOther
Tagetes erecta (African marigold)AsteraceaeOther
Talinum fruticosumPortulacaceaeOther
Tectona grandis (teak)LamiaceaeMain
Urtica dioica (stinging nettle)UrticaceaeWild host
Verbena brasiliensisVerbenaceaeOther
Washingtonia filifera (desert fanpalm)ArecaceaeOther
Zingiber officinale (ginger)ZingiberaceaeMain

Growth Stages

Top of page Vegetative growing stage

Symptoms

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Potato

Foliage: the first visible symptom is a wilting of the leaves at the ends of the branches during the heat of the day with recovery at night. As the disease develops, a streaky brown discoloration of the stem may be observed on stems 2.5 cm or more above the soil line, and the leaves develop a bronze tint. Epinasty of the petioles may occur. Subsequently, plants fail to recover and die. A white, slimy mass of bacteria exudes from vascular bundles when broken or cut.

Tubers: external symptoms may or may not be visible, depending on the state of development of the disease. Bacterial ooze often emerges from the eyes and stem-end attachment of infected tubers. When this bacterial exudate dries, soil masses adhere to the tubers giving affected tubers a 'smutty' appearance. Cutting the diseased tuber will reveal browning and necrosis of the vascular ring and in adjacent tissues. A creamy fluid exudate usually appears spontaneously on the vascular ring of the cut surface.

Atypical symptoms on potato (necrotic spots on the epidermis), possibly caused after lenticel infection, have been described by Rodrigues-Neto et al. (1984).

Symptoms of brown rot may be readily distinguished with those of ring rot caused by Clavibacter michiganensis subsp. sepedonicus (EPPO/CABI, 1997). R. solanacearum can be distinguished by the bacterial ooze that often emerges from cut stems and from the eyes and stem-end attachment of infected tubers. If cut tissue is placed in water, threads of ooze are exuded. Because such threads are not formed by other pathogens of potato, this test is of presumptive diagnostic value. For ring rot, tubers must be squeezed to press out yellowish dissolved vascular tissue and bacterial slime.

Tomato

The youngest leaves are the first to be affected and have a flaccid appearance, usually at the warmest time of day. Wilting of the whole plant may follow rapidly if environmental conditions are favourable for the pathogen. Under less favourable conditions, the disease develops slowly, stunting may occur and large numbers of adventitious roots are produced on the stem. The vascular tissues of the stem show a brown discoloration and drops of white or yellowish bacterial ooze may be released if the stem is cut (McCarter, 1991).

Tobacco

One of the distinctive symptoms is partial wilting and premature yellowing of leaves. Leaves on one side of the plant or even a half leaf may show wilting symptoms. This occurs because vascular infection may be restricted to limited sectors of stems and leaf petioles. In severe cases, leaves wilt rapidly without changing colour and stay attached to the stem. As in tomato, the vascular tissues show a brown discoloration when cut. The primary and secondary roots may become brown to black (Echandi, 1991).

Banana

On young and fast-growing plants, the youngest leaves turn pale green or yellow and collapse. Within a week all leaves may collapse. Young suckers may be blackened, stunted or twisted. The pseudostems show brown vascular discoloration (Hayward, 1983). Moko disease, caused by R. solanacearum, is easily confused with the disease caused by Fusarium oxysporum f.sp. cubense. A clear distinction is possible when fruits are affected - a brown and dry rot is only seen in Moko disease.

Teak

Seedling wilt manifests itself as yellowing of the mature lower leaves, which show scorching and browning of the tissue between the veins. The younger leaves and terminal shoot become flaccid and droop. Affected seedlings show either a gradual loss of leaf turgidity or sudden wilting. Seedling wilt becomes evident in the early hours of the day and gradually becomes more pronounced by midday, especially on sunny days. The wilted seedlings may partially recover during the afternoon and evening when temperatures fall, but wilting becomes more pronounced on successive days. The roots of affected seedlings exhibit a brownish-black discoloration. In advanced stages of disease, the tuberous portion of the root becomes discoloured and spongy. In due course, seedlings with pronounced wilt symptoms become completely desiccated.

In container nurseries, R. solanacearum infects the cotyledons of emerging seedlings causing greyish-brown, water-soaked lesions, which spread to the entire cotyledon and become necrotic. The infection spreads to the adjoining stem and root tissues and the affected seedlings rot and die. Collar rot appears in 1- to 4-month-old bare-root seedlings as greyish-brown, water-soaked lesions at the collar region of seedlings, just above the soil level. The lesions spread longitudinally on the stem, both above and below ground level, becoming sunken and necrotic. The younger leaves become flaccid and droop followed by leaf scorching and pronounced vascular wilt. In bare-root nurseries, wilt usually occurs in small patches affecting individuals or groups of seedlings, which expand as more seedlings succumb to the infection.

Infection of mature foliage begins as greyish-brown to greyish-black, irregular lesions that spread to the entire leaf lamina. Infection spreads to the petioles and stems.

List of Symptoms/Signs

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SignLife StagesType
Fruit / lesions: black or brown
Growing point / distortion
Growing point / wilt
Leaves / abnormal colours
Leaves / abnormal leaf fall
Leaves / abnormal patterns
Leaves / necrotic areas
Leaves / odour
Leaves / wilting
Leaves / yellowed or dead
Roots / cortex with lesions
Roots / rot of wood
Roots / soft rot of cortex
Stems / discoloration
Stems / discoloration of bark
Stems / internal discoloration
Stems / necrosis
Stems / ooze
Stems / rot
Stems / wilt
Vegetative organs / internal rotting or discoloration
Whole plant / damping off
Whole plant / discoloration
Whole plant / dwarfing
Whole plant / plant dead; dieback
Whole plant / seedling blight

Biology and Ecology

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Variation

R. solanacearum is represented by a heterogeneous population that has been reported variously as comprising groups, races, biovars, biotypes, sub-races and strains that have been impossible to codify in a unified nomenclature. The different classifications of R. solanacearum have caused considerable uncertainty. The commonly applied terms biovar and biotype refer to differences in biochemical and phage reactions (Hayward, 1962). Races (Buddenhagen et al., 1962) are distinguished on the basis of differences in plant host range.

Race 1 affects tobacco, tomato, potato, aubergine, diploid banana and many other (solanaceous) crops and weeds, and has a high temperature optimum (35-37°C).

Race 2 affects triploid bananas (causing Moko disease) and Heliconia spp. and has a high temperature optimum (35-37°C).

Race 3 mainly affects potatoes and tomatoes with lesser virulence to other solanaceous crops, and having a lower temperature optimum (27°C). Pelargonium can also be affected (Strider et al., 1981). Other hosts are the weeds Solanum dulcamara, S. nigrum, S. cinereum (in Australia), Urtica dioica (Urticaceae), Portulaca oleracea (Portulacaceae) and the composite weed Melampodium perfoliatum (in Costa Rica).

Two additional races separately affecting ginger (Zingiber officinale) and mulberry (Morus spp.) have also been characterized (Buddenhagen, 1986), but their status is still unclear.

There are many solanaceous and non-solanaceous plant species that are hosts to R. solanacearum. The can only be ascribed to known and possibly novel races when strains from them are isolated and examined.

Hayward (1964) distinguished four biotypes (biovars) by their ability to produce acid from six disaccharides and sugar alcohols and a phage reaction. Mulberry strains have been described as biovar 5 (Buddenhagen, 1986). These biovars do not generally correlate with the races of Buddenhagen et al. (1962) except that race 3 is equivalent to biovar 2 (Hayward, 1983). Races and biovars have been grouped into two major divisions according to their RFLP profiles (Cook and Sequeira, 1988, 1994). Asian strains of race 1 (biovars 3, 4, 5) clustered as a group (Division 'Asiaticum') while American strains of race 1 (biovar 1), race 2 (biovar 1) and race 3 (biovar 2) clustered as another group (Division 'Americanum'). This separation was later confirmed using other molecular markers. Division specific primers have been developed (Seal et al., 1999). A comparative study of PCR-RFLP profiles of the hrp gene region showed that strains from Reunion, Madagascar, Zimbabwe and Angola formed a separate cluster most similar to the Division 'Asiaticum' (Poussier et al., 1999).

Race 3 (biovar 2) appeared to be homogeneous in early molecular fingerprinting studies. However, when South American strains of race 3 (biovar 2) became available more variation was observed than had previously been reported. (a) 'Normal' strains were found east of the watershed of the Andes and all over the world; (b) strains that were biochemically different, found only west of the Andean divide; and (c) strains that were intermediate between race 1 and 3 from the lowlands of South America (also named biovar 2N or 2T). Strain types b and c have not yet been reported elsewhere (Janse, 1991; Gillings and Fahy, 1994; Hayward, 1994b; Smith et al., 1995). These findings, and the fact that resistance is found in wild Solanum phureja (Sequeira and Rowe, 1969), indicate that race 3 may have originated in South America.

Survival

Most plant pathogenic bacteria are usually closely associated with their living host plants and temporarily in infected host-plant debris. They survive for relatively brief periods in soil or other environments where competition is with active saprophytic populations. R. solanacearum is one of the few plant pathogenic bacteria for which there is evidence of survival in soil. Many weeds have been shown to be alternative hosts that maintain an on-going source of inoculum for the pathogen between crops. Race 3 survived for 2-3 years in Australia under bare fallow or pasture. Host debris, latent infected tubers and deeper soil layers were most important for survival (Graham and Lloyd, 1979; Graham et al., 1979).

Disease Development

Entry into plants is through wounds or stomata. Within the plant, the bacteria move in the vascular bundles, a process that is accelerated at higher temperatures. Speed of movement is also dependent on the plant part colonized. For instance, bacteria move more quickly in the stem than in the roots in tobacco (Ono et al., 1984). This is followed by colonization of the xylem (Xiao et al., 1983) where the bacteria adhere by polar attraction to the vessel walls, or invade the lumen. They subsequently become localized at preferential sites of the mesophyll (Petrolini et al., 1986). Blocking of the vessels by bacteria is considered to be the major cause of wilting. A histopathological comparison between susceptible and resistant Capsicum annuum was made by Rahman et al. (1999).

The disease is most severe at temperatures of 24-35°C and is seldom found where the mean temperature in winter falls below 10°C. There are specific temperature optima for disease development of the different races (biovars) (Swanepol, 1990).

High soil moisture and periods of wet weather or rainy seasons are associated with high disease incidence. Soil moisture also affects reproduction and survival of the pathogen; soil moisture levels of -0.5 to -1.0 bar favours disease expression whereas levels of -5 to -15 bar are unfavourable (Nesmith and Jenkins, 1985).

Weather conditions, such as low temperatures, that are unfavourable for disease expression can conceal extensive infection. In Kenya, certified healthy potato seed tubers produced at altitudes of 1520-2120 m expressed disease when planted at lower altitudes (Nyangeri et al., 1984).

For further information, see also Kelman (1953), OEPP/EPPO (1961), Buddenhagen and Kelman (1964), Persley (1986b) and Hayward (1994b).

Climate

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ClimateStatusDescriptionRemark
A - Tropical/Megathermal climate Preferred Average temp. of coolest month > 18°C, > 1500mm precipitation annually
Af - Tropical rainforest climate Preferred > 60mm precipitation per month
As - Tropical savanna climate with dry summer Tolerated < 60mm precipitation driest month (in summer) and < (100 - [total annual precipitation{mm}/25])
Aw - Tropical wet and dry savanna climate Preferred < 60mm precipitation driest month (in winter) and < (100 - [total annual precipitation{mm}/25])
B - Dry (arid and semi-arid) Tolerated < 860mm precipitation annually
BS - Steppe climate Tolerated > 430mm and < 860mm annual precipitation
BW - Desert climate Tolerated < 430mm annual precipitation
C - Temperate/Mesothermal climate Preferred Average temp. of coldest month > 0°C and < 18°C, mean warmest month > 10°C
Cf - Warm temperate climate, wet all year Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, wet all year
Cs - Warm temperate climate with dry summer Preferred Warm average temp. > 10°C, Cold average temp. > 0°C, dry summers
Cw - Warm temperate climate with dry winter Preferred Warm temperate climate with dry winter (Warm average temp. > 10°C, Cold average temp. > 0°C, dry winters)
D - Continental/Microthermal climate Tolerated Continental/Microthermal climate (Average temp. of coldest month < 0°C, mean warmest month > 10°C)
Df - Continental climate, wet all year Preferred Continental climate, wet all year (Warm average temp. > 10°C, coldest month < 0°C, wet all year)
Ds - Continental climate with dry summer Tolerated Continental climate with dry summer (Warm average temp. > 10°C, coldest month < 0°C, dry summers)
Dw - Continental climate with dry winter Tolerated Continental climate with dry winter (Warm average temp. > 10°C, coldest month < 0°C, dry winters)

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
60 60

Air Temperature

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Parameter Lower limit Upper limit
Mean annual temperature (ºC) -10 40

Natural enemies

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Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Bacillus cereus Pathogen
Bacillus licheniformis Pathogen
Bacillus polymixa Pathogen
Bacillus subtilis Pathogen
Burkholderia glumae Antagonist
Chainia flava Pathogen
Pseudomonas fluorescens Antagonist

Means of Movement and Dispersal

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Spread between countries usually involves vegetative propagating material that carries latent infections or is contaminated with the pathogen. Natural infection of true seed has only been established for groundnut (see Seed Transmission). Race 1 has been reported in tomato, Capsicum and aubergine seed (Persley, 1986b; Kelman et al., 1994; Singh, 1995) although till now poorly substantiated. As presently understood, soil-borne bacteria and transmission through vegetative plant parts are considered to be more important for most host plants as means of transmission of the pathogen than is true seed.

Race 2, which causes Moko disease of banana, is transmitted by insects and has a potential for rapid spread. Race 1 and 3 may be spread in water when infected riparian weeds such as Solanum dulcamara, Urtica dioica and Portulaca oleracea grow with their roots and stem parts in water. The bacterium may subsequently be spread to other hosts when contaminated water is used for irrigation (Olsson, 1976; Elphinstone et al., 1998; Janse et al., 1998, 2004; Farag et al., 1999Wenneker et al., 1999Alvarez et al., 2008; Tomlinson et al., 2009; Ustun et al., 2009).

Seed Transmission

Seed infection and disease transmission by seed caused by R. solanacearum has only been established for groundnut in Indonesia (Machmud and Middleton, 1990; Machmud, 1993) and China (Zhang et al., 1993; Dongfang et al., 1994). The bacterium was detected in the funiculus, pod shell, seed coat and embryo. The water content of the seed is an important factor in seed transmission and dry storage of seed severely impaired survival of the bacterium. It was suggested that dry preservation could lead to disease-free groundnut seed (Zhang et al., 1993). No other seed treatments have been reported.

Natural seed infection in tomato and aubergine has been suggested for race 1 of R. solanacearum (Shakya, 1993; Chatterjee et al., 1994; Singh, 1994). Artificial seed contamination of tomato and Capsicum has been observed (Devi and Menon, 1980; Moffett et al., 1981). Sites of survival on seed have not been identified.

Studies in Russia claim that the pathogen is transmitted with soyabean seeds (Klykov, 1951; Muras, 1964).

Seedborne Aspects

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Incidence

R. solanacearum has been shown to be seedborne in groundnut (Machmud and Middleton, 1991; Machmud, 1993; Zhang et al., 1993; Dongfang et al., 1994). The bacterium was detected in the funiculus, pod shell, seed coat and in the embryo (Machmud and Middleton, 1991; Machmud, 1993). Survival of R. solanacearum in groundnut seeds is closely related to the seed water content. The pathogen could not be detected in seeds with a water content of less than 10% (Zhang et al., 1993). R. solanacearum was not isolated from seeds stored for 1 year (Zeng et al., 1994).

A 38-100% incidence of infection of R. solanacearum was detected in aubergine seed collected from various regions of West Bengal, India. The pathogen survived well on seeds kept at 22°C and a relative humidity of 30-40%, but populations declined rapidly at 35°C or 50% RH (Chatterjee et al., 1994). Natural seed infection by R. solanacearum has also been reported in tomato (Shakya, 1993; Singh, 1994). The incidence of the bacterium was high in freshly extracted, non-sterilized seeds and fruit pulp obtained from tomatoes on plants inoculated through the leaf axil. Incidence was considerably reduced on surface-sterilized or dried seeds and the bacterium was not found in the embryo (Devi and Menon, 1980). R. solanacearum was detected among bacteria isolated from 46 samples of clover seed (Nikitina, 1974). The pathogen is reported as being seedborne on soyabean (Muras, 1963; Nikitina and Korsakov, 1978). These reports indicate that transmission of the pathogen from a diseased crop to succeeding crops grown from seed harvested from that crop is likely.

Pathogen Transmission

True Seed

When seeds from wilted groundnut plants were sown, they produced wilted plants at a frequency of 5-8% (Machmud and Middleton, 1991; Hong et al., 1994). In a similar study, seeds from wilted plants of both tomato and aubergine yielded pathogenic isolates of R. solanacearum. Seed infection usually resulted in wilting of adult plants. Seed from healthy plants obtained from a bacterial wilt infested field showed no evidence of the pathogen. However, no relationship was found between percentage seed infection and ultimate plant mortality (Roopali-Singh and Singh, 1994). Moffett et al. (1981) demonstrated transmission of R. solanacearum to plants grown from tomato seeds artifically inoculated with 20,000 bacteria/seed. Sanchez-Perez et al. (2008) also report unexplained contamination of tomato seed through artificial inoculation.

Other sources

R. solanacearum has been shown to survive on plant residues for 2-3 years (Muras, 1963, 1964) and this is undoubtedly an important inoculum source for this pathogen. Infected seed potatoes, rhizomes of ginger and turmeric and other vegetative propagation material are also vehicles for the spread of R. solanacearum. Surface water contaminated with R. solanacearum is another important factor (Elphinstone, 1996; Elphinstone et al., 1998; Janse et al., 1998; Farag et al., 1999; Wenneker et al., 1999). The bacterium can also survive on wood (several days), metal (several weeks), rubber (several months), chicken and cattle manure (2-4 weeks) and waste from the potato processing industry (1-2 months) (Wenneker et al., 1998).

Seed Treatment

Long-term dry storage of groundnut seed reduced survival of R. solanacearum. It has been suggested that dry preservation could lead to disease-free groundnut seed (Zhang et al., 1993).

Ultrasonic radiation of soyabean seeds reduced cotyledon infection in plants grown from these seeds (Krasnova, 1963). Phytobacteriocin reduced disease incidence and increased yield (Muras, 1964). Granosan, thiram and mercuran gave effective control (Klykov, 1951, 1963).

The application of chitosan as a seed treatment reduced wilt incidence by 48%, and the application of the Paenibacillus polymyxa strain MB02-1007 reduced wilt incidence by 88% (Algam et al. 2010).

Seed Health Tests

Dilution plating (Kelman, 1954; Singh, 1994)

Twenty-five seeds are ground and suspended in 1 ml sterile distilled water. 0.1 ml of the suspension is plated on a semi-selective medium (Kelman, 1954; Singh, 1994) or placed directly on this medium. The development of distinctive mucoid magenta-pigmented colonies indicates the presence of the pathogen.

Grow-out
Seeds are germinated and seedlings tested for the presence of the pathogen (Shakya, 1993).

ELISA test
Rajeshwari et al. (1998) developed an ELISA test using polyclonal sera against the virulence exopolysaccharide component for detection of R. solanacearum in seed.

Note: An effective selective medium has been developed that may be used successfully for isolations from seed (Engelbrecht, 1994), modified by Elphinstone et al. (1996).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
Biological control Yes Yes Anderson and Gardner, 1999; Paret et al., 2008
Breeding and propagation Yes Yes
Crop productionFrequent accidental or deliberate for use as biocontrol agent for Hedychium gardnerianum in tropical Yes Yes
Cut flower trade Yes Yes
Food Yes
Forage Yes
Horticulture Yes Yes
Industrial purposespotato processing industry when not using waste treatment or waste treatment with only aerobic steps Yes Yes Janse, 2012; Janse et al., 1998
Interconnected waterways Yes
Landscape improvementmud from cleaning waterways which is then spread on fields. Yes

Pathway Vectors

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VectorNotesLong DistanceLocalReferences
Clothing, footwear and possessionsTransfer of vegetative germplasm. Yes
Debris and waste associated with human activities Yes
Floating vegetation and debris Yes
Germplasm Yes Yes
Land vehicles Yes
Machinery and equipment Yes Fortnum and Gooden, 2008
MailTransfer of vegetative germplasm. Yes
Plants or parts of plants Yes Yes
Soil, sand and gravelWater. Yes
Water Yes

Plant Trade

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Plant parts liable to carry the pest in trade/transportPest stagesBorne internallyBorne externallyVisibility of pest or symptoms
Bulbs/Tubers/Corms/Rhizomes Yes Pest or symptoms usually visible to the naked eye
Flowers/Inflorescences/Cones/Calyx Yes Pest or symptoms usually visible to the naked eye
Fruits (inc. pods) Yes Pest or symptoms usually visible to the naked eye
Growing medium accompanying plants Yes Pest or symptoms usually invisible
Roots Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Seedlings/Micropropagated plants Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Stems (above ground)/Shoots/Trunks/Branches Yes Pest or symptoms not visible to the naked eye but usually visible under light microscope
Plant parts not known to carry the pest in trade/transport
Bark
True seeds (inc. grain)
Wood

Impact Summary

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CategoryImpact
Economic/livelihood Negative

Impact

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Introduction

R. solanacearum is the most serious pathogen of solanaceous plants in tropical regions and can cause serious losses in temperate regions. Accurate data on yield losses and further economic impacts are not available. A review of the older literature can be found in Kelman (1953). A method to determine yield loss/disease severity for brown rot in potato has been described (Elphinstone, 1989). New high-yeilding but susceptible cultivars in place of older tolerant varieties, may cause problems in areas where the disease is endemic (Weingartner and Shumaker, 1984).

Many factors influence disease incidence and yield loss. In a study in India on sesame wilt incidence was significantly correlated with mean temperature, rainfall and relative humidity during the crop growth period (Hazarika and Das, 1999). In a study on the effects of physical soil properties it was found that sandy loam soil with a high sand content and low silt or clay content, with low water-holding capacity, was unfavourable for the pathogen and wilt incidence. Elevated disease levels were expressed in clay soils with high water-holding capacities (Keshwal et al., 2000).

Root colonization by ectomycorrhizal fungi is important in reducing disease levels and increasing tree growth in Eucalyptus spp. In China, disease in nurseries was reduced by 40-72% and in fields by 20-39% when seedlings were inoculated with eight fungal isolates. Height and basal diameter growth of trees in field trials were enhanced by 11.7 to 59.7% (Gong et al., 1999).

Greatest economic losses have been reported on potato, tobacco and tomato in the south-eastern USA, Indonesia (Sunarjono, 1980), Nepal, Uganda (Busolo-Bulafu et al., 1993), Brazil (Melo et al., 1999), Colombia and South Africa. In the Philippines, there were average losses of 15% in tomato, 10% in aubergine and Capsicum, and 2-5% in tobacco (Zehr, 1969). In the Amazon basin in Peru, banana plantations have been seriously affected with rapid spread of the pathogen in previously unaffected plantations (French and Sequeira, 1968). In India, there are sometimes total losses in tomato crops. Bacterial wilt also appears to be very common in wild and cultivated turmeric (Curcuma spp.) in Thailand and Indonesia (Thammakijjawat et al., 1999). Bacterial wilt is also a problem in ginger (Zingiber officinale); it was present in 80% of 310 fields surveyed in Himachal Pradesh, India (Sharma and Rana, 1999), and severe losses were reported from Thailand (Titatarn, 1985).

R. solanacearum has been intercepted regularly from rhizomes exported for cut flower production in Europe. The disease may cause serious indirect losses when quarantine measures entail restriction movement of, or destruction of plant products (Hyde et al., 1992; Tuin et al., 1996).

Potato

Multiplication by cutting seed potato seriously increases the risk of high losses. Cut seed potato increased disease incidence by 250% and reduced yield by 40% (Vijayakumar et al., 1985). Extensive losses of potato were reported in Greece (Zachos, 1957). In Israel, losses were heavier in the spring potato crop than the autumn crop, because of the higher growing temperatures in spring (Volcani and Palti, 1960). Tuber rotting averaged 10%, reaching 50%, in stored potatoes in Nepal (Shrestha, 1996). Complete crop losses in small holdings in Nepal resulted from poor cultural practices including using seed from affected crops for subsequent plantings (Gurung and Vaidya, 1997). In Venezuela, in the period 1992-1996, R. solanacearum was found in most localities between 1100 and 3000 m above sea level, but was not found in localities at altitudes greater than 3000 m. Bacterial wilt disease incidence increased from 22% in 1992 to 37% in 1996 with disease incidence varying between 5 and 75%. Biovar 2 was present in greatest frequency and in most of the affected areas for potato (Garcia et al., 1999).

Tomato

In tomato hybrids, field grown in Taiwan for the fresh market, bacterial wilt incidence was 15-26% on improved tolerant hybrids compared to 55% in other hybrids (Hartman et al., 1991). In India, an investigation of the effect of time of infection showed that disease incidence, measured by plant mortality and plant yield, diminished with age of the plant at the time of inoculation. Maximum losses were recorded during the summer season (Kishun, 1987).

Groundnuts and Other Crops

In Vietnam, infection in groundnut was most severe in dryland cropping systems, especially on sandy soils along riverbanks, and on uplands (Hong et al., 1994). Tolerant varieties are infected by the pathogen but are not affected and can produce high yields (Liao et al., 1998). Bacterial wilt in groundnut (Race 1, biovars 3 and 4) is widespread in China. Annual disease incidence ranges from 4 to 8% on resistant cultivars. Pathogenicity varies between regions, the disease generally being more serious in southern provinces where losses of up to 20% were common (Yeh, 1990; Tan et al., 1994). Disease severity mostly increases if R. solanacearum is found in association with root nematodes. In tobacco, nematode infestation leads to greater susceptibility to bacterial wilt (Chen, 1984). When bacterial wilt of teak was initially recorded during the 1980s in Kerala, India, it appeared to be of little consequence. However, the incidence of the disease has increased over the years, both in nurseries and plantations. R. solanacearum causes mortality of bare-root and root trainer seedlings raised in high rainfall areas. Young plantations raised in waterlogged sites in areas of high rainfall (>3000 mm per annum) are more seriously affected. In these areas, the incidence of disease varied from <1% to ca 20% (Sharma et al., 1985). Synergistic interactions between R. solanacearum and Meloidogyne javanica have been reported (Sitaramaiah and Sinha, 1984; ; Verma et al., 1997; Pathak et al., 1999).

Environmental Impact

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When R. solanacearum establishes itself in riparian weed hosts (especially bittersweet, Solanum dulcamara) along rivers, the bacterium may (and did) spread via water and those hosts into nature reserves, where it is usually impossible and/or forbidden to control these weeds. This poses no threats to the nature reserves, but it may pose a problem for growers when they use surface water for irrigation. This is why in the Netherlands a nationwide ban for irrigation of seed potatoes is in place (Janse, 1996, 2012; Wenneker et al., 1999; Elphinstone et al., 1998; Elphinstone and Harris, 2002).

Risk and Impact Factors

Top of page Invasiveness
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Tolerant of shade
  • Fast growing
  • Has high reproductive potential
  • Has propagules that can remain viable for more than one year
  • Reproduces asexually
  • Has high genetic variability
Impact outcomes
  • Host damage
  • Negatively impacts agriculture
Impact mechanisms
  • Pathogenic
  • Rapid growth
Likelihood of entry/control
  • Difficult/costly to control

Diagnosis

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Isolation is best made from early infection stages, small pieces of tissue being excised from the margins preferably of the youngest lesions. These are comminuted in small quantities of sterile water and streaked on TTC medium (Schaad et al., 2001) or very good selective medium SMSA developed by Engelbrecht (1994) and modified by Elphinstone et al. (1996) and incubated at 25-27°C for 2 days. Isolation can also be readily made by streaking suspensions of bacterial ooze obtained from cut infected tissue. The development of largely unmixed mucoid magenta colonies on TTC medium or is a good indication that the pathogen has been isolated. Single colonies are sub-cultured onto nutrient agar for storage and confirmation of the identity of the pathogen using the tests described in Schaad et al. (2001).

Biochemical tests, fatty acid analysis, RFLP and protein analysis can be used for identification purposes (Seal et al., 1993; Seal and Elphinstone, 1994; Anon., 1997, 1998, 2006; Stephani and Mazzucchi, 1997; Hartung et al., 1998; Wullings et al., 1998; Seal et al., 1999; OEPP/EPPO, 2004).

Highly specific and sensitive molecular probes based on unique DNA sequences obtained by DNA subtraction methods can readily be developed for the pathogen to confirm the identity of the pathogen including strains obtained from symptomless plants. These methods are only used when a high level of confidence in identification is necessary to support eradication programmes or quarantine restrictions that may involve compensation.

Nitrocellulose membrane (NCM)-ELISA kits were used by Bekele et al. (2011) to confirm the presence of bacterial wilt, caused by R. solanacearum, in potato leaves.

The use of colony PCR-SSCP technique for the diagnosis of R. solanacearum is described in Umesha et al. (2012), and is advocated by Chandrakeshar et al. (2012). A method for the identification of R. solanacearum race 2 is describe in Gund et al. (2011).

Detection and Inspection

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The bacterium may be obtained from infected tubers or stems for staining purposes if a small portion of tissue is pressed onto a clean glass slide. Potato tubers can be visually checked for internal symptoms by cutting. Suspect tubers should be diagnosed in the laboratory. Appropriate laboratory methods to detect the pathogen have been laid down in a harmonized EU-interim scheme for detection of the brown rot bacterium (Anon., 1997). These methods are based on earlier described indirect immunofluorescence antibody staining (IFAS). Standard samples of 200 tubers per 25 t of potatoes are taken (Janse, 1988; OEPP/EPPO, 1990a; Anon., 1997, 1998, 2006). Recently a very effective selective medium has been described (Engelbrecht, 1994, and modified by Elphinstone et al., 1996), that can also be applied for detection in environmental samples such as surface water, soil and waste (Janse et al., 1998; Wenneker et al., 1999). ELISA and PCR, based on 16S rRNA targeted primers as well as fluorescent in-situ hybridization (FISH) using 16S and 23S rRNA-targeted probes have also been used.

Ralstonia syzygii, causal agent of Sumatra disease of clove (Syzygium) and the distinct Blood Disease Bacterium, causal agent of blood disease of banana in Indonesia, are closely related to R. solanacearum and cross-react in serological and DNA-based detection methods (Wullings et al., 1998; Thwaites et al., 1999).

Similarities to Other Species/Conditions

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Brown rot symptoms caused by R. solanacearum in potato may be confused with those caused by Clavibacter michiganensis subsp. sepedonicus, agent for ring rot of potato. Brown rot usually develops earlier in the season and is more rapid than ring rot. For ring rot, leaves show intercostal yellowing, which is absent with brown rot, and bacterial slime does not exude spontaneously from the tuber. Only when the tuber is pressed does a mass of whitish-to-yellow macerated vascular tissue and bacterial slime emerge. Soil does not stick to the heel end or eyes of ring rot-infected tubers.

Symptoms of bacterial wilt in tomato may be confused with those caused by Clavibacter michiganensis subsp. michiganensis, agent of bacterial canker. This disease is expressed as white, necrotic spots on the leaves that are absent in bacterial wilt. Adventitious root formation seen in wilt is absent in bacterial canker, whereas the vascular discoloration in canker is more yellow in colour than in bacterial wilt.

For Moko disease on banana, symptoms may be confused with those of Fusarium oxysporum f.sp. cubense. A brown and dry rot of the fruits is present only in the case of Moko disease. Moko disease can also be confused with banana blood disease, caused by the so-called blood disease bacterium (Ralstonia sp. nr solanacearum), occurring in Indonesia (Eden-Green, 1994).

Prevention and Control

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Control of bacterial wilt is very difficult, largely being dependent on good crop management practices.

The use of certified disease-free seed, reliable and early detection of the pathogen, quarantine measures on infected fields and farms, sufficient crop rotation, control of weed hosts, volunteer plants and nematodes where present, avoidance of surface water for irrigation, and education are key factors in control (Janse, 1996; Pradhanang and Elphinstone, 1996b).

Seed potato tubers and seed of other solanaceous plants should be obtained from crops that have been inspected and found disease-free for the last two growing seasons. Visual inspections should be performed routinely upon export and import. Laboratory checks for low level infection and contamination may be necessary. Plants of Musa spp. should be kept in post-entry quarantine (OEPP/EPPO, 1990b).

Cutting seed potato tubers should be avoided. Crop rotation of 5-7 years without susceptible crops has been recommended. The disease may also be controlled by the application of fertilizers to change soil pH. In the USA, lowering the soil pH to 4-5 in summer and raising it to pH 6 in the autumn eradicated the pathogen (Graham and Lloyd, 1979; Graham et al., 1979).

Tolerant cultivars of potato, aubergine (Dalal et al., 1999; Quezado-Soares et al., 1997), tobacco, groundnut and other crops are available, but the race and strain diversity of the pathogen means that cultivars must be selected with care. Potato cultivars were selected in Colombia with tolerance derived from Solanum phureja and S. demissum (French, 1985; Hartman and Elphistone, 1994). Tobacco-resistant cultivars have been developed (Lopez et al., 1978).

In China, wilt-resistant groundnut cultivars appear to be the most important control measure (Tan et al., 1994) although they have a lower yield potential due to reduced nodulation and nitrogen fixation by Rhizobium bacteria (Liao et al., 1992).

Because tolerant plants may be infected and contaminated with the pathogen without symptom expression (Grimault and Prior, 1993) movement of these cultivars into disease-free regions may introduce the pathogen.

Grafting of aubergine on resistant Solanum species has been shown to be successful (Mochizuki and Yamakawa, 1979). Grafting of tomato on resistant aubergine rootstock reduced losses by 90% (Lum and Wong, 1976). A new technique of raising brinjal seedlings on coir piths has shown some promise in controlling the disease. Once transplanted, the plants are immune to diseases for about 30-40 days, after which they are not greatly affected by bacterial wilt (ProMED-Plant, 2010).

Resistance in tomato and other hosts may be reduced by nematode infection (Yen et al., 1997; Deberdt et al., 1999).

Intercropping of potato with maize or Phaseolus vulgaris reduced inoculum density and disease development in some cases (Autrique and Potts, 1987) but the pathogen was found to persist in these alternative hosts (Granada and Sequeira, 1983). In a crop rotation trial it was found that resting land for 3 years reduced wilt from 80.1 to less than 7.5%. Tuber rot was reduced and crop yield enhanced. For potato, a minimum fallow period of 2 years appeared to be adequate to obtain good yields (Matao et al., 1982).

Wilt severity in tomato was reduced by a rotation system using maize, okra, cowpea or resistant tomato. The onset of bacterial wilt was delayed by 1-3 weeks and wilt severity was reduced by 20-26% (Adhikari and Basnyat, 1998). Tomato in rotation with rice was also effective in reducing R. solanacearum populations in Taiwan (Michel et al., 1996).

Rotation of groundnut with rice and with maize, wheat, sorghum and sugarcane was effective in reducing incidence and severity (Hong et al., 1994; Tan et al., 1994). In tobacco, disease incidence was reduced and the yield was increased by cultivar resistance and by 1-year rotation with maize, fescue (Festuca sp.) or soyabean (Melton and Powell, 1991).

Hot-air treatment of ginger roots for 30 min at 50°C has been successful (Tsang and Shintaku, 1998). Treatment of soils using stable bleaching powder gave disease suppression of 70-89% in greenhouse and field trials (Dhital et al., 1997) and in combination with deep ploughing (Kishore et al., 1996). Data collected over 3 years revealed that pre-treatment of soil with bleaching powder controlled the disease by 68.4% (Verma and Shekhawat, 1991). Effects of soil amendments are soil dependent (Michel and Mew, 1998). Soil fumigants showed either slight or no effects (Murakoshi and Takahashi, 1984). Some compounds based on hydrogen peroxide and peracetic acids (and catalase-inhibitors) show promising results for disinfection of contaminated surface water (Janse et al., 1998; Niepold, 1999).

Chemical control is ineffective. Antibiotics, streptomycin, ampicillin, tetracycline and penicillin showed hardly any effect (Farag et al., 1982); in fact, streptomycin application increased the incidence of bacterial wilt in Egypt (Farag et al., 1986). Biological control has been investigated, but efficacious biocontrol agents have yet to be developed. Positive results were achieved in laboratory experiments with the antagonistic bacteria Bacillus polymyxa and Pseudomonas fluorescens (Aspiras and Cruz, 1985). Success has been claimed for P. fluorescens in potato in laboratory and field trials. Avirulent mutants of the bacterium have also been used in some studies (See Ciampi-Panno et al., 1989; Gallardo and Panno, 1989; Hartman and Elphinstone, 1994).

References

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===, 1978. Data sheets on quarantine organisms. Set 1. Bulletin, Organisation Europeenne et Mediterraneenne pour la Protection des Plantes, 8(2).

1990. Quarantine procedure No. 26. Pseudomonas solanacearum. Inspection and test methods. Bulletin OEPP, 20(2):255-262

Abdalla MY; Al-Mihanna AA; Al-Rokibah AA; Ibrahim GH, 1999. Tomato bacterial wilt in Saudi Arabia and the use of antagonistic bacteria for its control. Annals of Agricultural Science (Cairo), 44(2):511-521; 25 ref.

Adhikari TB; Basnyat RC, 1998. Effect of crop rotation and cultivar resistance on bacterial wilt of tomato in Nepal. Can. J. Plant Pathol. 20:283-287.

Alfenas AC; Mafia RG; Sartório RC; Binoti DHB; Silva RR; Lau D; Vanetti CA, 2006. Ralstonia solanacearum on eucalyptus clonal nurseries in Brazil. (Ralstonia solanacearum em viveiros clonais de eucalipto no Brasil.) Fitopatologia Brasileira, 31(4):357-366. http://www.scielo.br/pdf/fb/v31n4/05.pdf

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Anderson RC; Gardner DE, 1999. An evaluation of the wilt-causing bacterium Ralstonia solanacearum as a potential biological control agent for the alien kahili ginger (Hedychium gardnerianum) in Hawaiian forests. Biological Control, 15(2):89-96; 27 ref.

Andrade FWRde; Amorim EPda R; Eloy AP; Rufino MJ, 2009. Occurence of banana diseases in the state of Alagoas. (Ocorrência de doenças em bananeiras no estado de Alagoas.) Summa Phytopathologica, 35(4):305-309. http://www.scielo.br/pdf/sp/v35n4/a08v35n4.pdf

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Anonymous, 1998. Council Directive 98/57/EC of 20 July 1998 on the control of Ralstonia solanacearum. Annex II-test scheme for the diagnosis, detection and identification of Ralstonia solanacearum. Official Journal of the European Communities, L235:8-39.

Anonymous, 2006. Commission Directive 2006/63/EC of 14 July 2006: amending Annexes II to VII to Council Directive 98/57/EC on the control of Ralstonia solanacearum (Smith) Yabuuchi et al. Official Journal of the European Communities, L206:36-106.

ARAGAKI M; QUINON VL, 1965. Bacterial wilt of ornamental Gingers (Hedychium spp.) caused by Pseudomonas solanacearum. Plant Disease Reporter, 49(5):378-379.

Aspiras RB; Cruz ARde la, 1985. Potential biological control of bacterial wilt in tomato and potato with Bacillus polymyxa FU6 and Pseudomonas fluorescens.. Bacterial wilt disease in Asia and the South Pacific., 89-92; [ACIAR Proceedings No. 13]; 13 ref.

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Banani Chatterjee; Chakraborty M; Habib AKMA; Samaddar KR, 1994. Survival of Pseudomonas solanacearum biovar 3 on seeds of eggplant. Bacterial Wilt Newsletter, No. 11:11

Banymandhub-Munbodh K; Lalouette JA; Bachraz DY; Sukurdeep N; Seebaluck BD, 1998. In: Lalouette JA, Bachraz DY, Sukurdeep N, Seebaluck BD, eds. Studies on bacterial wilt caused by Ralstonia solanacearum syn. Burkholderia solanacearum syn. Pseudomonas solanacearum on Anthurium andreanum. Proceedings of the Second Annual Meeting of the Agricultural Scientists, Reduit, Mauritius, 12-13 August, 1997: 195-201.

Bekele B; Abate E; Asefa A; Dickinson M, 2011. Incidence of potato viruses and bacterial wilt disease in the west Amhara sub-region of Ethiopia. Journal of Plant Pathology, 93(1):149-157. http://sipav.org/main/jpp/index.php/jpp/article/view/285/151

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Black R; Delbeke A, 1991. Moko disease (Pseudomonas solanacearum) of Musa in Belize. Tropical Science, 31(4):347-353

Black R; Seal S; Abubakar Z; Nono-Womdim R; Swai I, 1999. Wilt pathogens of Solanaceae in Tanzania: Clavibacter michiganensis subsp. michiganensis, Pseudomonas corrugata, and Ralstonia solanacearum. Plant Disease, 83(11):1070; 4 ref.

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