Foodplant / pathogen
Xanthomonas campestris pv. campestris infects and damages live, yellow-blotched leaf of Crambe maritima
Foodplant / pathogen
Xanthomonas campestris pv. campestris infects and damages live, yellow-blotched leaf of Brassicaceae
Foodplant / pathogen
Xanthomonas campestris pv. campestris infects and damages live, yellow-blotched leaf of Brassica
Other: major host/prey
Xanthomonas campestris pv. campestris
Black rot, caused by the bacterium Xanthomonas campestris pv. campestris (Xcc), is considered the most important and most destructive disease of crucifers, infecting all cultivated varieties of brassicas worldwide. This disease was first described by botanist and entomologist Harrison Garman in Lexington, Kentucky, USA in 1889. Since then, it has been found in nearly every country in which vegetable brassicas are commercially cultivated.
Host infection by Xcc can occur at any stage of the plant life cycle. Characteristic symptoms of black rot caused by Xcc are V-shaped chlorotic to necrotic lesions extending from the leaf margins and blackening of vascular tissues.
The pathogen thrives in warm and humid climates and is rapidly disseminated in the field. Use of clean seed, crop rotation, and other cultural practices are the primary means of control of black rot. However, in developing countries such as those in South and Eastern Africa, black rot remains the greatest impediment to cabbage cultivation due to unreliable "clean" seed, multiple croppings annually, and high susceptibility of popular local cultivars to the disease.
Hosts and symptoms
Members of the plant family Brassicaceae (Cruciferae), which includes cabbage, broccoli, cauliflower, kale, turnip, oilseed rape, mustard, radish, and the model organism Arabidopsis thaliana are affected by black rot.
Host infection by Xcc causes V-shaped chlorotic to necrotic foliar lesions, vascular blackening, wilting, stunted growth, and stem rot symptoms. As the pathogen proceeds from the leaf margins towards the veins, water stress and chlorotic symptoms develop due to occlusion of water-conducting vessels by bacterial exopolysaccharides and components of degraded plant cell walls. The darkening of vascular tissues following bacterial invasion gives the black rot disease its name. Lesions produced by Xcc may serve as portals of entry for other soft-rot pathogens such as Pectobacterium carotovorum (formerly Erwinia carotovora) and Pseudomonas marginalis.
These symptoms may be confused with fusarium wilt of cabbage (fusarium yellows), caused by the fungus Fusarium oxysporum f. sp. conglutinans. In contrast to black rot, in which the pathogen invades leaf margins and causes chlorotic to necrotic symptoms that progress downwards in the plant, fusarium wilt symptoms first develop in the lower portions of the plant and move upwards. Furthermore, leaf veins invaded by Xcc turn black compared to the dark brown vein discoloration found in fusarium wilt.
Symptoms of black rot may vary widely among different species of crucifers. On cauliflower, Xcc infection via stomates causes black or brown specks, scratched leaf margins, black veins, and discolored curds. Additionally, the severity of symptoms and aggressiveness of the disease varies between different strains of the Xcc pathogen. The isolates can be differentiated into races based on the reaction of several Brassica lines after inoculation. A race structure including 5 races (0 to 4) was first proposed in 1992; a revised classification model with 6 races was proposed in 2001 and, more recently, the model was expanded to include nine races.
The primary source of inoculum is Xcc infected seed. During germination, the seedling becomes infected through the epicotyl  and cotyledons may develop blackened margins, shrivel, and drop. The bacteria progress through the vascular system to the young stems and leaves, where the disease manifests as V-shaped chlorotic to necrotic lesions extending from the leaf margins. Under humid conditions, bacteria present in guttation droplets can be spread by wind, rain, water splashes, and mechanical equipment to neighboring plants.
The natural route of invasion by Xcc is through the hydathodes, though leaf wounds caused by insects and plant roots may also be portals of entry. Occasionally, infections occur through stomata. Hydathodes provide the pathogen a direct path from the leaf margins to the plant vascular system and thus systemic host infection. Invasion of the suture vein leads to production of Xcc infected seed.
Xcc can survive in plant debris in soil for up to 2 years, but not more than 6 weeks in free soil. Bacteria present in plant debris can serve as a source of secondary inoculum.
Warm and wet conditions favor plant infection by Xcc and the development of disease. Free moisture is required for host invasion, considering that the natural route of infection is through the hydathodes.
The optimum temperature range for bacterial growth and host symptom development is between 25° to 30 °C . A slower rate of growth is observed at temperatures as low as 5 °C and up to 35 °C. However, infected hosts are symptomless below 18 °C.
- Use of certified disease-free seeds and transplants
- Hot water treatment of non-certified seeds; chemical treatments with sodium hypochlorite, hydrogen peroxide, and hot cupuric acetate or zinc sulfate may also be used
- Control of insects
- Crop rotation with non-cruciferous plants (3-4 years)
- Removal of crop debris after harvest
- Control of cruciferous weeds that may serve as reservoir for the pathogen
- Sanitation (e.g. clean equipment, avoiding work in wet fields, etc.)
The development and use of black rot resistant cultivars has long been recognised as an important method of control, but in practice has had limited success. Resistance to the most important pathogenic races of Xcc is rare in B. oleracea (e.g. cabbage, broccoli, cauliflower); the most common and potentially useful sources of black rot resistance occur in other brassica genomes including B. rapa, B. nigra, B. napus, B. carinata and B. juncea.
Cabbage cultivation is a multi-billion dollar industry worldwide, reflecting its value as a vegetable crop, source of vegetable oil, component of fodder crop for livestock feed, and ingredient in condiments and spices. In 2007, the cabbage crop in the US exceed $413M (1.4M+ tons). Black rot is considered the most important disease of cabbage and other crucifers because Xcc infections may not become apparent until the warm summer months (well after planting), the pathogen spreads rapidly, and losses due to the disease may exceed 50% in warm, wet climates. The importance of using disease-free seed and/or transplants is highlighted by the fact that “as few as three infected seeds in 10,000 (0.03%) can cause black rot epidemics in a field.” In transplant beds, an initial infection level of 0.5% can rise to 65% in just three weeks. In fact more recent work  indicates that spread can be much more rapid than this: with overhead gantry irrigation, spread of the pathogen greatly exceeded symptom spread to the extent that in one experiment almost 100% of the transplants were infested in a block of 15 module trays (approx. 4500 plants) six weeks after sowing from a single primary infector. Modelling of the rate of spread in transplants indicates that the widely used tolerance standard for seed health testing (0·01%) should be revised to 0·004% 
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|This article includes a list of references, related reading or external links, but its sources remain unclear because it lacks inline citations. (October 2010)|
Xanthomonas campestris is bacterial species that causes a variety of plant diseases. Available from the NCPPB,and other international Culture collections such as ICMP, ATCC, and LMG in a purified form, it is used in the commercial production of a high-molecular-weight polysaccharide - xanthan gum - that is an efficient viscosifier of water and that has many important uses, especially in the food industry.
Types of Xanthomonas campestris
- Xanthomonas campestris pv. armoraciae
- Xanthomonas campestris pv. begoniae A
- Xanthomonas campestris pv. begoniae B
- Xanthomonas campestris pv. campestris
- Xanthomonas campestris pv. carota
- Xanthomonas campestris pv. corylina
- Xanthomonas campestris pv. dieffenbachiae
- Xanthomonas campestris pv. hederae
- Xanthomonas campestris pv. hyacinthi
- Xanthomonas campestris pv. juglandis - the walnut blight
- Xanthomonas campestris pv. malvacearum or Xanthomonas citri subsp. malvacearum 
- Xanthomonas campestris pv. musacearum
- Xanthomonas campestris pv. nigromaculans
- Xanthomonas campestris pv. pelargonii
- Xanthomonas campestris pv. phaseoli
- Xanthomonas campestris pv. poinsettiicola
- Xanthomonas campestris pv. raphani
- Xanthomonas campestris pv. sesami
- Xanthomonas campestris pv. tardicrescens
- Xanthomonas campestris pv. translucens
- Xanthomonas campestris pv. vesicatoria
The former pv. citri, which causes citrus canker, was reclassified as X. axonopodis in 1995 Xanthomonas campestris#cite note-0. In 2006, the species designations for pv. citri and malvacearum were revised to X. citri and these pathovars are now referred to as subspecies Xanthomonas campestris#cite note-1.
Gerhard Reuther, Martin Bahmann: Elimination of Xanthomonas campestris pv. pelargonii by Means of Micropropagation of Pelargonium Stock Plants; In: 3rd International Geranium Conference, 1992. Proceedings, Ball Publishing Batavia, IL. USA ; (1992),
- Schaad NW, Postnikova E, Lacy GH, Sechler A, Agarkova I, Stromberg PE, Stromberg VK, Vidaver AK (2006). "Emended classification of xanthomonad pathogens on citrus." Syst Appl Microbiol 29(8): 690-695.
- Vauterin L, Hoste B, Kersters K, and Swings J (1995). "Reclassification of Xanthomonas." Int J Syst Bacteriol 45: 472-489.
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Banana Xanthomonas wilt
Banana Xanthomonas Wilt (BXW), or banana bacterial wilt (BBW) or enset wilt is a bacterial disease caused by Xanthomonas campestris pv. musacearum. After being originally identified on a close relative of banana, Ensete ventricosum, in Ethiopia in the 1960s, BXW emanated in Uganda in 2001 affecting all types of banana cultivars. Since then BXW has been diagnosed in Central and East Africa including banana growing regions of: Rwanda, Democratic Republic of the Congo, Tanzania, Kenya, Burundi, and Uganda.
Of the numerous diseases infecting bananas, BXW alongside banana bunchy top virus has been the most devastating in recent years. Global concern arose over the livelihoods of African banana farmers and the millions relying on bananas as a staple food when the disease was at its worst between the years 2001 and 2005. It was estimated that in Central Uganda from 2001 and 2004, there was a 30-52 % decease in banana yield due to BXW infection. Although extensive management of the disease outbreaks has helped reduce the impact of Banana Xanthomonas Wilt even today BXW continues to a pose a real problem to the banana farmer of Central and East Africa.
BXW symptoms can be sorted into two domains: symptoms on the inflorescence and symptoms on the fruit. Symptoms on the fruit are usually used to distinguish BXW from alternative banana diseases. A bacterial ooze is excreted from the plant organs and this is a mandatory sign that BXW may be present. Common symptoms on the fruit include internal discoloration and premature ripening of the fruit. A cross section of the BXW infected banana is characterized by the yellow- orange discoloration of the vascular bundles and dark brown tissue scaring. Symptoms on the inflorescence include a gradual wilting and yellowing of the leaves plus wilting of the bracts and shriveling of the male buds. Many factors may affect the combination of disease symptoms on show. These include the particular cultivar infected, how the disease has been transmitted and the current growing season.
Soil is one of the main sources for Xanthomonas campestris pv. musacearum inoculum. Xanthomonas campestris pv. musacearum may contaminate the soil for four months and more. BXW awareness campaigns have helped reduce the numbers of farmers growing bananas on contaminated plantains aiding in the control of the disease overall. Transmission of contaminated disease itself is thought to be low.
It widely thought that Xanthomonas campestris pv. musacearum bacteria is transmitted to airborne vectors through exposed male flowers (see plant reproductive morphology). Xanthomonas campestris pv. musacearum bacteria has been isolated from the ooze and nectar excreted from openings of fallen male flowers. Insects, namely stingless bees (Apidae), fruit flies (Drosophilidae) and grass flies (Chloropidae), transmit the disease from banana to banana after being drawn to the infected nectar. If the disease has been transmitted by insects the symptoms tend to first appear on the male buds of the banana plant.
The knife (panga) is used almost universally in African agriculture. Use of contaminated knives was a common method for disease spread when the disease first originated but increased knowledge of BXW transmission has led to increased numbers knives being disinfected after use. Herbicides are now advised as a more economical and effective way of destroying infected banana crop.
Infected plant material
BXW infects all parts of the plant. Disease spread has been primarily linked with the transport of plants shoots for replanting. Other parts of the plant such as the male buds (used in banana beer production) and mulch (banana waste material) can also expose novel regions to the disease.
Control of BXW is based upon a variety of methods to help prevent the spread of the disease. Vigilance and the quick removal of infected plants remain critical to minimising spread of the disease.
Infected plants can be removed using herbicides or more commonly by cutting the plant into small fragments and decomposing. The risk of infection can be lowered by removal of the male bud ('debudding') but many farmers believe this is essential to the quality of the banana fruit. The risk of infection decreases if the plants are not covered with topsoil. However the risk of disease should be balanced against the resulting decrease in yield of the banana plantain. A major part of disease control is the disinfecting of the tools used.
Much of the work in controlling BXW has been done through educational campaigns raising awareness of the disease to the banana farmers. For example: in Uganda and Tanzania where the government has actively worked alongside farmers to help limit spread of the disease, over 90% control of BXW has been reported. Moreover much of the information taught to the farmers can be used in the control of other banana infecting diseases.
BXW resistant banana
No banana cultivars in Central and Eastern Africa have shown any resistance to BXW despite some varieties, such as those in the 'Pisang Awak' region, showing increased susceptibility. Scientists have recently transferred two genes from sweet green pepper to bananas in order to confer resistance to BXW. This is a promising step forward in circumventing the time consuming and expensive practices of disease management such as 'debudding'.
Pflp and Hrap genes encoding the proteins plant ferredoxin-like amphipathic protein (pflp) and hypersensitive response-assisting protein (hrap) were isolated from sweet pepper and introduced to the genome of East African bananas using genetic engineering. The two proteins induced a hypersensitive response and systemic acquired resistance within the banana plant after being exposed to the bacterial pathogen. It was reported that over half of the transgenic bananas were resistant to BXW.
- Tushemereirwe, W. Kangire, A. Ssekiwoko, F. Offord, L.C. Crozier, J. Boa, E. Rutherford, M. Smith J.J. (2004). "First report of Xanthomonas campestris pv. musacearum on banana in Uganda". Plant Pathology 53: 802.
- Bradbury, J.F. Yiguro, D. (1968). "Bacterial wilt of Enset ("Ensete ventricosa") incited by "Xanthomonas musacearum".". Phytopathology 58: 111–112.
- Mwangi, M. Bandyopadhyay, R. Ragama,P. Tushemereirwe, R.K. (2007). "Assessment of banana planting practices and cultivar tolerance in relation to management of soilborne Xanthomonas campestris pv. musacearum". Crop Protection 26: 1203–1208.
- Karamura, E. et al. (2010). "Assessing the Impacts of Banana Bacterial Wilt Disease on Banana(Musa spp.) Productivity and Livelihoods of Ugandan Farm Households.". Acta Horticulture (ISHS) 879: 749–755.
- Biruma, M. et al. (2007). "Banana Xanthomonas wilt: a review of the disease, management strategies and future research directions". African Journal of Biotechnology 6: 953–962.
- Abele, s. et al. (2009). "Xanthomonas Wilt A threat to banana production in East and Central Africa". Plant Disease: 439–451.
- Tinzaaara, W. et al. (2006). The possible role of insects in the transmission of Banana Xanthomonas Wilt. Programme and Abstract Book of the 4th International Bacterial Wilt Symposium. p. 60.
- Smith, J.J. et al. (2008). "An analysis of the risk from Xanthomonas campestris pv. musacearum to banana cultivation in Eastern, Central and Southern Africa". Biodiversity International.
- Blomme, G. Turyagyenda, L.F Mukasa, H. Eden-Green, S. (2008). "The effectiveness of different herbicides in the destruction of Banana Xanthomonas Wilt infected plants". African Crop Science Journal 16: 103–110.
- Namukwaya, B. et al. (2012). "Transgenic banana expressing Pflp gene confers enhanced resistance to Xanthomonas wilt disease". Transgenic Resistance 21: 855–865.
- Tripathi, L. Mwaka, H. Tripathi, J.N. Tushemereirwe, W.K. (2010). "Expression of sweet pepper Hrap gene in banana enhances resistance to Xanthomonas campestris pv. musacearum". Molecular Plant Pathology 6: 721–731.