Tospovirus
Encyclopedia
The Tospoviruses are a genus
(Tospovirus) of negative RNA virus
found within the family
Bunyaviridae
. They are the sole group of plant infecting viruses in this family, as all other described members of the Bunyaviridae infect animals. The genus takes its name from the discovery of Tomato spotted wilt virus (TSWV) in Australia
in 1915. It remained the only member of the family until the early 1990s when genetic characterisation of viruses discovered in plants became more common. There are now at least twenty viral "species" in the family with more being recorded and described on a relatively regular basis. Together, these viruses have been documented infecting over eight hundred different plant species from 82 different families.
genome
with negative polarity, therefore it is classified as a Class V virus ((-)ssRNA viruses). The structure of the genome resembles that of the genus Phlebovirus. The genome is linear and is 17.2 kb in size. It is segmented 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 orientation.
. At least ten species of thrips belonging to family Thripidae
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 .
There are a large number of plant families that are known to be affected by viruses of the Tospovirus genus. These include both food crops (such as peanuts
, watermelon
s, capsicums, tomato
es, zucchini
s, et al.) as well as ornamental species which are important to flower farms (calla lily
, impatiens
, crysanthemums
, iris
, et al.). For a more complete list of hosts examine the Tospovirus host list at Kansas State University
.
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.
Inclusions found in leaf strips of plants infected with a Tospovirus
. 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. 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.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
(Tospovirus) of negative RNA virus
RNA virus
An RNA virus is a virus that has RNA as its genetic material. This nucleic acid is usually single-stranded RNA but may be double-stranded RNA...
found within the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Bunyaviridae
Bunyaviridae
Bunyaviridae is a family of negative-stranded RNA viruses. Though generally found in arthropods or rodents, certain viruses in this family occasionally infect humans. Some of them also infect plants....
. They are the sole group of plant infecting viruses in this family, as all other described members of the Bunyaviridae infect animals. The genus takes its name from the discovery of Tomato spotted wilt virus (TSWV) in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
in 1915. It remained the only member of the family until the early 1990s when genetic characterisation of viruses discovered in plants became more common. There are now at least twenty viral "species" in the family with more being recorded and described on a relatively regular basis. Together, these viruses have been documented infecting over eight hundred different plant species from 82 different families.
Genome
This virus has a single stranded RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
with negative polarity, therefore it is classified as a Class V virus ((-)ssRNA viruses). The structure of the genome resembles that of the genus Phlebovirus. The genome is linear and is 17.2 kb in size. It is segmented 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 orientation.
Transmission
Tospoviruses are arboviruses usually vectored by a thripsThrips
Thrips are tiny, slender insects with fringed wings . Other common names for thrips include thunderflies, thunderbugs, storm flies, thunderblights, and corn lice...
. At least ten species of thrips belonging to family Thripidae
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 antennae of six to ten antennomeres with stiletto-like...
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 the virus 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.There are a large number of plant families that are known to be affected by viruses of the Tospovirus genus. These include both food crops (such as peanuts
Peanuts
Peanuts is a syndicated daily and Sunday American comic strip written and illustrated by Charles M. Schulz, which ran from October 2, 1950, to February 13, 2000, continuing in reruns afterward...
, watermelon
Watermelon
Watermelon is a vine-like flowering plant originally from southern Africa. Its fruit, which is also called watermelon, is a special kind referred to by botanists as a pepo, a berry which has a thick rind and fleshy center...
s, capsicums, tomato
Tomato
The word "tomato" may refer to the plant or the edible, typically red, fruit which it bears. Originating in South America, the tomato was spread around the world following the Spanish colonization of the Americas, and its many varieties are now widely grown, often in greenhouses in cooler...
es, zucchini
Zucchini
The zucchini is a summer squash which often grows to nearly a meter in length, but which is usually harvested at half that size or less. It is a hybrid of the cucumber. Along with certain other squashes, it belongs to the species Cucurbita pepo. Zucchini can be dark or light green...
s, et al.) as well as ornamental species which are important to flower farms (calla lily
Calla Lily
-Botany:* Calla, a genus of common flowering plant in the family Araceae, containing the single species Calla palustris, native to cool temperate regions of the Northern Hemisphere...
, impatiens
Impatiens
Impatiens is a genus of about 850–1,000 species of flowering plants, widely distributed throughout the Northern Hemisphere and tropics. Together with the puzzling Hydrocera triflora, this genus makes up the family Balsaminaceae...
, crysanthemums
Chrysanthemum
Chrysanthemums, often called mums or chrysanths, are of the genus constituting approximately 30 species of perennial flowering plants in the family Asteraceae which is native to Asia and northeastern Europe.-Etymology:...
, iris
Iris (plant)
Iris is a genus of 260-300species of flowering plants with showy flowers. It takes its name from the Greek word for a rainbow, referring to the wide variety of flower colors found among the many species...
, et al.). For a more complete list of hosts examine the Tospovirus host list at Kansas State University
Kansas State University
Kansas State University, commonly shortened to K-State, is an institution of higher learning located in Manhattan, Kansas, in the United States...
.
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. FruitFruit
In broad terms, a fruit is a structure of a plant that contains its seeds.The term has different meanings dependent on context. In non-technical usage, such as food preparation, fruit normally means the fleshy seed-associated structures of certain plants that are sweet and edible in the raw state,...
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
Impatiens necrotic spot virus
SummaryImpatiens necrotic spot virus ' is a plant pathogenic virus of the family Bunyaviridae. It was originally believed to be another strain of Tomato spotted wilt virus but genetic investigations revealed them to be separate viruses...
(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.
Inclusions found in leaf strips of plants infected with a Tospovirus
Epidemology
TSWV is prevalent in warm climates in regions with a high population of thrips. This virus 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 occidentalisFrankliniella occidentalis
The western flower thrips is an important pest insect in agriculture. This species of thrips is native to North America but has spread to other continents including Europe, Australia, and South America via transport of infested plant material...
. Another thrips, Scirtothrips dorsalis
Scirtothrips dorsalis
The chilli thripsThis is the more common international spelling of "chilli" outside of the United States. This spelling has been preserved in the common name for the insect by entomologists in the United States in deference to the body of literature already published for this species by...
, has also been implicated in the transmission of at least three tospoviruses, but there remains some controversy over its efficiency as a vector. 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 this disease is difficult. One of the reasons for this is that the wide host range allows the virus 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.Resources
- The Complete Tospovirus Resource Page at KSUKansas State UniversityKansas State University, commonly shortened to K-State, is an institution of higher learning located in Manhattan, Kansas, in the United States...
- Tospoviruses:Bunyaviridae from Plant Viruses online
- Plant Viruses Online – Tomato Spotted Wilt tospovirus
- 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 [doi:10.1038/npg.els.0000760]
- ICTVdB - The Universal Virus Database: Tomato spotted Cake virus
- Family Groups - The Baltimore Method
- Tospoviruses (Family Bunyaviridae, Genus Tospovirus) An article by Scott Adkins, Tom Zitter and Tim Momol.