Candidatus Liberibacter

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Candidatus Liberibacter
Potato psyllid.jpg
The potato psyllid, Bactericera cockerelli , feeds on a potato and infects it with Candidatus Liberibacter solanacearum, the bacterium that causes zebra chip disease.
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Candidatus Liberibacter

Jagoueix et al., 1997
Species

See text

Candidatus Liberibacter is a genus of Gram-negative bacteria in the Rhizobiaceae family. The term Candidatus indicates that it has not proved possible to maintain this bacterium in culture. Detection of the liberibacters is based on PCR amplification of their 16S rRNA gene with specific primers. Members of the genus are plant pathogens mostly transmitted by psyllids. The genus was originally spelled Liberobacter. [1]

Contents

Most importantly, Candidatus Liberibacter is a causative agent of Huanglongbing disease (HLB) also known as citrus greening disease. [2] Candidatus Liberibacter is transmitted by two insects from Psyllidae family – Diaphorina citri in Asia, Brazil and Florida, and Trioza erytreae in Africa. The Asian HLB strain, Candidatus Liberibacter asiaticus is more heat tolerant, while the African strain, Candidatus Liberibacter africanus is asymptomatic at temperatures above 30°C. [2] Species of Candidatus Liberibacter, infecting solanaceous plants has been identified and it was carried by another psyllid, a potato pest Bactericera cockerelli. [2] [3]

Pathogenicty

Candidatus Liberibacter are carried in the hemolymph and salivary glands of psyllids. Since psyllids feed on sap, this provides bacteria the entry to phloem of the plant. [2] They induce significant metabolic and regulatory changes that damage the plants transport system and affects plants defense systems. These impairments have downstream negative effects on citrus microbiome of the infected plants. [4]

Since Candidatus Liberibacter cannot be cultivated outside of its vector or host, genetics, bacteria-vector and bacteria-plant interaction have not yet been thoroughly explored. Factors important for adaption and colonization or possible coevolution are not yet understood. [2] [4] Liberibacter activates salicylic acid pathway in host, likely due to recognition of extracellular molecules such as lipopolyscacharides or flagella. Pathogen in turn likely mitigates the effects, because it encodes SA hydroxylase, that degrades salicylic acid. Liberibacters were shown to affect the spread of vector, by influencing the flight frequencies and sexual attraction of D. citri. On the other hand, infection with Liberibacter causes higher mortality of D. citri adults, but not nymphs. [4] Liberibacter is a part of the psyllid microbiota and co-existence with other bacteria likely has impact on the overall fitness of the insect, as well as outcome of the disease. [4]

Treatment

Primary strategy for HLB disease management is a vector control. Antimicrobial treatment can suppress Candidatus Liberibacter spp., however usage of broad spectrum antibiotics is inadvisable due to adverse environmental effects. Alternative treatments, such as heat therapy, i.e. incubation of plant at temperatures above 40°C for several days, show varying effects. Another suggested alternatives include the use of compounds that alleviate disease symptoms and boost plants defense systems or reinforcing natural citrus microbiota in order to compete with Candidatus Liberibacter spp. [5] http://citrusindustry.net/2019/06/19/update-on-brassinosteroids-for-hlb-management/ https://portal.nifa.usda.gov/web/crisprojectpages/1005557-zinkicide-a-nanotherapeutic-for-hlb.html

Species

Named species include: [6]

Related Research Articles

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Citrus production

Citrus production encompasses the production of citrus fruit, which are the highest-value fruit crop in terms of international trade. There are two main markets for citrus fruit:

Psyllidae Family of true bugs

Psyllidae, the jumping plant lice or psyllids, are a family of small plant-feeding insects that tend to be very host-specific, i.e. each plant-louse species only feeds on one plant species (monophagous) or feeds on a few closely related plants (oligophagous). Together with aphids, phylloxerans, scale insects and whiteflies, they form the group called Sternorrhyncha, which is considered to be the most "primitive" group within the true bugs (Hemiptera). They have traditionally been considered a single family, Psyllidae, but recent classifications divide the group into a total of seven families; the present restricted definition still includes more than 70 genera in the Psyllidae. Psyllid fossils have been found from the Early Permian before the flowering plants evolved. The explosive diversification of the flowering plants in the Cretaceous was paralleled by a massive diversification of associated insects, and many of the morphological and metabolic characters that the flowering plants exhibit may have evolved as defenses against herbivorous insects.

Phytoplasma Family of bacteria

Phytoplasmas are obligate bacterial parasites of plant phloem tissue and of the insect vectors that are involved in their plant-to-plant transmission. Phytoplasmas were discovered in 1967 by Japanese scientists who termed them mycoplasma-like organisms. Since their discovery, phytoplasmas have resisted all attempts at in vitro culture in any cell-free medium; routine cultivation in an artificial medium thus remains a major challenge. Although phytoplasmas have recently been reported to be grown in a specific artificial medium, experimental repetition has yet to be reported. Phytoplasmas are characterized by the lack of a cell wall, a pleiomorphic or filamentous shape, a diameter normally less than 1 μm, and a very small genome.

Citrus greening disease Bacterial disease of citrus, bug-borne

Citrus greening disease is a disease of citrus caused by a vector-transmitted pathogen. The causative agents are motile bacteria, Candidatus Liberibacter spp. The disease is vectored and transmitted by the Asian citrus psyllid, Diaphorina citri, and the African citrus psyllid, Trioza erytreae, also known as the two-spotted citrus psyllid. It has also been shown to be graft-transmissible. Three different types of HLB are currently known: The heat-tolerant Asian form, and the heat-sensitive African and American forms. The disease was first described in 1929 and first reported in China in 1943. The African variation was first reported in 1947 in South Africa, where it is still widespread. Eventually, it affected the United States, reaching Florida in 2005. Within three years, it had spread to the majority of citrus farms. The rapid increase in this disease has threatened the citrus industry not only in Florida, but the entire US. As of 2009, 33 countries have reported HLB infection in their citrus crop.

<i>Xylella fastidiosa</i> Bacteria harming plants, including crops

Xylella fastidiosa is an aerobic, Gram-negative bacterium of the monotypic genus Xylella. It is a plant pathogen, and is transmitted exclusively by xylem fluid feeding sap insects. Many plant diseases are due to symptomatic infections of X. fastidiosa, including bacterial leaf scorch, oleander leaf scorch, coffee leaf scorch (CLS), alfalfa dwarf, phony peach disease, and the economically important Pierce's disease of grapes (PD) and citrus variegated chlorosis (CVC). In Europe it has attacked olive trees in the Salento area of Southern Italy causing the olive quick decline syndrome (OQDS). While distributions of X. fastidiosa–related diseases are mostly limited to the Americas, outbreaks have occurred in Taiwan, Slovakia, and other countries worldwide.

<i>Alternaria</i> Genus of fungi

Alternaria is a genus of [Deuteromycetes] fungi. Alternaria species are known as major plant pathogens. They are also common allergens in humans, growing indoors and causing hay fever or hypersensitivity reactions that sometimes lead to asthma. They are present in the human mycobiome and readily cause opportunistic infections in immunocompromised people such as AIDS patients.

<i>Ralstonia solanacearum</i> Disease bacteria of tomato family, others

Ralstonia solanacearum is an aerobic non-spore-forming, Gram-negative, plant pathogenic bacterium. R. solanacearum is soil-borne and motile with a polar flagellar tuft. It colonises the xylem, causing bacterial wilt in a very wide range of potential host plants. It is known as Granville wilt when it occurs in tobacco. Bacterial wilts of tomato, pepper, eggplant, and Irish potato caused by R. solanacearum were among the first diseases that Erwin Frink Smith proved to be caused by a bacterial pathogen. Because of its devastating lethality, R. solanacearum is now one of the more intensively studied phytopathogenic bacteria, and bacterial wilt of tomato is a model system for investigating mechanisms of pathogenesis. Ralstonia was until recently classified as Pseudomonas, with similarity in most aspects, except that it does not produce fluorescent pigment like Pseudomonas. The genomes from different strains vary from 5.5 Mb up to 6 Mb, roughly being 3.5 Mb of a chromosome and 2 Mb of a megaplasmid. While the strain GMI1000 was one of the first phytopathogenic bacterias to have its genome completed, the strain UY031 was the first R. solanacearum to have its methylome reported. Within the R. solanacearum species complex, the four major monophyletic clusters of strains are termed phylotypes, that are geographically distinct: phylotypes I-IV are found in Asia, the Americas, Africa, and Oceania, respectively.

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<i>Bactericera cockerelli</i> Species of true bug

Bactericera cockerelli, also known as the potato psyllid, is a species of psyllid native to southern North America. Its range extends from Central America north to the American Pacific Northwest and parts of Manitoba. It is restricted to the western part of the continent. As its name suggests, it is commonly found on potato and tomato crops, but has a species range that encompasses over 40 species of solanaceous plants and as many as 20 genera. Breeding hosts are generally recognised as being restricted primarily to Solanaceae, including important crop and common weed species, and a few species of Convolvulaceae, including bindweed and sweet potato. On some plants, especially potato, feeding of the nymphs causes a condition called psyllid yellows, presumed to be the result of a toxin. Both nymphs and adults can transmit the bacterium Candidatus Liberibacter.

Psyllid yellows is a disease of potatoes infested by the potato/tomato psyllid, Bactericera cockerelli. The symptoms are a marked yellowing of the leaves, an upright appearance to the leaves, with severe cases resulting in early death of the plant. Tuber initiation and growth is affected. Many small tubers are formed, frequently misshaped. In some cases, the tubers seem to have lost sprouting inhibition and have begun sprouting before harvest. At later stages, the tubers sprout weakly, if at all.

Zebra chip Plant disease in potatoes

Zebra chip, also known as papa manchada and papa rayada, is a disease in potatoes putatively caused by an alphaproteobacteria "Candidatus Liberibacter solanacearum", which is vectored by the potato psyllid. When fried, potato tubers from infected plants develop unsightly black lines resembling the stripes of zebras that render the chips unsellable. Additionally, striped sections of chips frequently burn and caramelize, resulting in a bitter flavor. No health risks have been connected with consumption of infected potato chips.

<i>Diaphorina citri</i> Species of true bug

Diaphorina citri, the Asian citrus psyllid, is a sap-sucking, hemipteran bug in the family Liviidae. It is one of two confirmed vectors of citrus greening disease. It has a wide distribution in southern Asia and has spread to other citrus growing regions.

The African citrus psyllid is a sap-sucking insect, a hemipteran bug in the family Triozidae. It is an important pest of citrus, being one of only two known vectors of the serious citrus disease, huanglongbing or citrus greening disease. It is widely distributed in Africa. The other vector is the Asian citrus psyllid, Diaphorina citri.

In biology, a pathogen in the oldest and broadest sense, is any organism that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

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<i>Candidatus</i> Phytoplasma fraxini Species of bacterium

CandidatusPhytoplasma fraxini is a species of phytoplasma, a specialized group of bacteria which lack a cell wall and attack the phloem of plants. This phytoplasma causes the diseases ash yellows and lilac witches' broom.

<i>Tamarixia radiata</i> Species of wasp

Tamarixia radiata, the Asian citrus cyllid parasitoid, is an hymenopteran wasp from the family Eulophidae which was discovered in the 1920s in the area of northwestern India (Punjab), now Pakistan. It is a parasitoid of the Asian citrus psyllid, an economically important pest of citrus crops around the world and a vector for Citrus greening disease.

Māori potatoes or taewa are varieties of potato cultivated by Māori people, especially those grown before New Zealand was colonised by the British.

References

  1. Taxonomy browser
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  14. Evidence that the Zebra Chip Disease and the Putative Causal Agent Can be Maintained in Potatoes by Grafting and In Vitro
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Further reading