''Orthotospovirus'' is a genus of negative-strand RNA viruses, in the family ''

Tospoviridae ''Orthotospovirus'' is a genus of Negative-strand RNA virus, negative-strand RNA viruses, in the family ''Tospoviridae'' of the order ''Elliovirales,'' which infects plants. Tospoviruses take their name from the species Tomato spotted wilt virus ( ...

'' of the order '' Elliovirales,'' which infects plants. Tospoviruses take their name from the species Tomato spotted wilt virus (TSWV) which was discovered in Australia in 1919. TSWV remained the only known member of the family until the early 1990s when genetic characterisation of plant viruses became more common. There are now 28 species in the genus with more being discovered on a regular basis. Member viruses infect over eight hundred plant species from 82 different families.

Genome

Tospoviruses have a

negative-sense In molecular biology and genetics, the sense of a nucleic acid molecule, particularly of a strand of DNA or RNA, refers to the nature of the roles of the strand and its complement in specifying a sequence of amino acids. Depending on the context, ...

, single-strand

RNA Ribonucleic acid (RNA) is a polymeric molecule that is essential for most biological functions, either by performing the function itself (non-coding RNA) or by forming a template for the production of proteins (messenger RNA). RNA and deoxyrib ...

genome A genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding genes, other functional regions of the genome such as ...

. The genome resembles that of the genus '' Phlebovirus''. It is linear and is 17.2 kb in size. It is divided into three segments termed S (2.9kb), M (5.4kb), and L (8.9kb). The M and S RNA segments encode for proteins in an ambisense direction.

Transmission

Tospoviruses are arboviruses usually vectored by

thrips Thrips (Order (biology) , order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Entomologists have species description , described approximately 7,700 species. They fly on ...

. At least ten species of thrips belonging to family

Thripidae The Thripidae are the most speciose family of thrips, with over 290 genera representing just over two thousand species. They can be distinguished from other thrips by a saw-like ovipositor curving downwards, narrow wings with two veins, and ante ...

have been confirmed as vectors for the transmission of thirteen or more tospoviruses. The thrips vectors are not closely related, implying an independent origin of infection for each thrips, possibly transmitted horizontally through shared hosts. There may be other species of thrips competent to transmit similar viruses, but they have not been documented on crops of economic significance. Recent research concludes that thrips can only be infected by tospovirus during the larval phases of development, as pupation and metamorphosis separate the connection between the salivary glands and the infected muscle tissue of the mid-gut. Adults transmit the virus from infected salivary glands, and uninfected adults will not transmit the virus. Obviously, controlling the infection by limiting transmission from infected plants to larval thrips or by preventing adult dispersal from infected plants are key strategies in preventing an epidemic of the disease.

Agricultural importance

Infection with these viruses results in spotting and wilting of the plant, reduced vegetative output, and eventually death. No antiviral cures have been developed for plants infected with a Tospovirus, and infected plants should be removed from a field and destroyed in order to prevent the spread of the disease. A large number of plant families are known to be affected by viruses of the ''Tospovirus'' genus. These include both food crops (such as

peanut The peanut (''Arachis hypogaea''), also known as the groundnut, goober (US), goober pea, pindar (US) or monkey nut (UK), is a legume crop grown mainly for its edible seeds. It is widely grown in the tropics and subtropics by small and large ...

watermelon The watermelon (''Citrullus lanatus'') is a species of flowering plant in the family Cucurbitaceae, that has a large, edible fruit. It is a Glossary of botanical terms#scandent, scrambling and trailing vine-like plant, and is plant breeding ...

s, capsicums,

tomato The tomato (, ), ''Solanum lycopersicum'', is a plant whose fruit is an edible Berry (botany), berry that is eaten as a vegetable. The tomato is a member of the nightshade family that includes tobacco, potato, and chili peppers. It originate ...

es,

zucchini Zucchini (; : ''zucchini'' or ''zucchinis''), courgette () or ''Cucurbita pepo'' is a summer squash, a Vine, vining herbaceous plant whose fruit are harvested when their immature seeds and Fruit anatomy#Epicarp, epicarp (rind) are still soft a ...

s, ''et al.'') as well as ornamental species which are important to flower farms ( calla lily,

impatiens ''Impatiens'' is a genus of more than 1,000 species of flowering plants, widely distributed throughout the Northern Hemisphere and the tropics. Together with the genus ''Hydrocera'' (one species), ''Impatiens'' make up the family (biology), f ...

chrysanthemum Chrysanthemums ( ), sometimes called mums or chrysanths, are flowering plants in the Asteraceae family. They are native to East Asia and northeastern Europe. Most species originate from East Asia, and the center of diversity is in China. Co ...

s, iris, ''et al.''). For a more complete list of hosts examine the Tospovirus host list at

Kansas State University Kansas State University (KSU, Kansas State, or K-State) is a public university, public Land-grant university, land-grant research university with its main campus in Manhattan, Kansas, United States. It was opened as the state's land-grant coll ...

Diagnosis

Early symptoms of infection are difficult to diagnose. In young infected plants the characteristic symptoms consist of inward cupping of leaves and leaves that develop a bronze cast followed by dark spots. As the infection progresses additional symptoms develop which include dark streaks on the main stem and wilting of the top portion of the plant.

Fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

may be deformed, show uneven ripening and often have raised bumps on the surface. Once a plant becomes infected the disease cannot be controlled. Serological and molecular tests are commercially available to diagnose TSWV as well as a second common tospovirus found in ornamentals, '' Impatiens necrotic spot virus'' (INSV). Cytological studies of TSWV and INSV have shown that these viruses produce granular inclusions in the cytoplasm of infected plants. These inclusions can be seen in the light microscope with proper staining techniques. These inclusions can be diagnostic.

Epidemiology

Tospoviruses are prevalent in warm climates in regions with a high population of thrips. For instance TSWV is an agricultural pest in Asia, America, Europe and Africa. Over the past 15 years outbreaks of Tomato spotted wilt disease have become more prevalent in these regions. Therefore, TSWV is described as an emerging viral disease of plants. The increased prevalence is largely because of the successful survival of the thrips vector '' Frankliniella occidentalis''. Another thrips, '' Scirtothrips dorsalis'', has also been implicated in the transmission of at least three tospoviruses, but there remains some controversy over its efficiency as a vector.Whitfield AE, Ullman DE, German TL (2005). Tospovirus-thrips interactions. Annual Review of Phytopathology. 43: 459–89. Immunological testing and vector-competence studies suggest that ''S. dorsalis'' may represents a non-transmitting carrier for some strains of virus. The success of this virus has also been attributed to the acquisition of a gene in the M segment of the genome which encodes a movement protein. This protein allows the virus to infect a wide range of hosts. The gene encoding this protein was likely acquired by recombination from either a plant host or from another plant virus.

Management

Control of these diseases is difficult. One of the reasons for this is that the wide host range allows the viruses to successfully overseason from one crop to the next. To prevent spread of the virus infected plants should be immediately removed away from neighbouring plants. Control of insects, especially thrips, is important to reduce spread of the virus by vectors.

Taxonomy

The genus contains the following species, listed by scientific name and followed by the exemplar virus of the species: * ''Orthotospovirus alstroemeriflavi'', Alstroemeria yellow spot virus * ''Orthotospovirus alstroemerinecrosis'', Alstroemeria necrotic streak virus * ''Orthotospovirus arachianuli'', Groundnut ringspot virus * ''Orthotospovirus arachiflavamaculae'', Groundnut yellow spot virus * ''Orthotospovirus arachiflavi'', Groundnut chlorotic fan-spot virus * ''Orthotospovirus arachinecrosis'', Groundnut bud necrosis virus * ''Orthotospovirus callaflavi'', Calla lily chlorotic spot virus * ''Orthotospovirus capsiciflavi'', Capsicum chlorosis virus * ''Orthotospovirus capsicimaculaflavi'', Pepper chlorotic spot virus * ''Orthotospovirus chrysanthinecrocaulis'', Chrysanthemum stem necrosis virus * ''Orthotospovirus citrullomaculosi'', Watermelon silver mottle virus * ''Orthotospovirus citrullonecrosis'', Watermelon bud necrosis virus * ''Orthotospovirus cucurbichlorosis'', Zucchini lethal chlorosis virus * ''Orthotospovirus eustomae'', Lisianthus necrotic ringspot virus * ''Orthotospovirus fatsiae'' Fatsia japonica ringspot-associated virus * ''Orthotospovirus glycininecrovenae'', Soybean vein necrosis virus * ''Orthotospovirus hippeflavi'', Hippeastrum chlorotic ringspot virus * ''Orthotospovirus impatiensnecromaculae'', Impatiens necrotic spot virus * ''Orthotospovirus iridimaculaflavi'', Iris yellow spot virus * ''Orthotospovirus meloflavi'', Melon yellow spot virus * ''Orthotospovirus melotessellati'', Melon severe mosaic virus * ''Orthotospovirus morivenae'', Mulberry vein banding associated virus * ''Orthotospovirus phaseolinecrotessellati'', Bean necrotic mosaic virus * ''Orthotospovirus polygonianuli'', Polygonum ringspot virus * ''Orthotospovirus tomatanuli'', Tomato yellow ring virus * ''Orthotospovirus tomatoflavi'', Tomato chlorotic spot virus * ''Orthotospovirus tomatomaculae'', Tomato spotted wilt virus * ''Orthotospovirus tomatozonae'', Tomato zonate spot virus

Resources

The Complete Tospovirus Resource Page
at KSU
Tospoviruses:Bunyaviridae
from Plant Viruses online

APSnet A Plant Disease Lesson on ''Tomato spotted wilt virus''
* Raccah. B (2000). ''Plant Virus Transmission by Insects. In: Encyclopedia of Life Sciences''. John Wiley & Sons, Ltd: Chichester. www.els.net

* ttp://www.virology.net/Big_Virology/BVFamilyGroup.html Family Groups - The Baltimore Method
Tospoviruses (Family ''Bunyaviridae'', Genus ''Tospovirus'')
An article by Scott Adkins, Tom Zitter and Tim Momol.

References

External links

Virus Pathogen Database and Analysis Resource (ViPR): Bunyaviridae
{{Taxonbar, from=Q2716408 Tospoviridae Tomato diseases Viral plant pathogens and diseases Virus genera