Transmission and lifespan

TSWV, which is transmitted by

thrips Thrips ( order Thysanoptera) are minute (mostly long or less), slender insects with fringed wings and unique asymmetrical mouthparts. Different thrips species feed mostly on plants by puncturing and sucking up the contents, although a few are ...

, causes serious losses in economically important crops and it is one of the most economically devastating plant viruses in the world. The circulative propagative transmission of TSWV is carried out by at least ten different species of thrips. The most common species is ''Frankliniella occidentalis'' (

western flower thrips The western flower thrips 'Frankliniella occidentalis'' (Pergande)is an invasive pest insect in agriculture. This species of thrips is native to the Southwestern United States but has spread to other continents, including Europe, Australia (wher ...

) as it is the

vector Vector most often refers to: *Euclidean vector, a quantity with a magnitude and a direction *Vector (epidemiology), an agent that carries and transmits an infectious pathogen into another living organism Vector may also refer to: Mathematic ...

that predominantly transmits TSWV globally and in

greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...

s. The rapid developmental and reproductive rate of the thrips contributes to the spread of TSWV. The amount of time it takes for insects to acquire the virus (acquisition period) and the amount of time it takes for the virus to move from the insect to the plant (inoculation) for TSWV varies depends on the vector species. For ''Frankliniella occidentalis'', the acquisition and inoculation of TSWV can be as short as 5 minutes. However, the acquisition and inoculation periods for optimal transmission is 21.3 hours and 42.7 hours, respectively. Transmission of TSWV can only occur when

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e stage thrips acquire TSWV. The larvae stage for thrips lasts around 1–3 days. TSWV is acquired by thrips when they feed on infected plants. Adult thrips cannot be infected with TSWV as their midgut barrier successfully prevents infection. However, thrips that have successfully become infected with TSWV in the larvae stage can transmit the virus throughout their lifetime. In order to protect their eggs, thrips insert their eggs into various types of plant tissue. Eggs can be found in the stems, leaves, or flowers of plants. Thrips hatch in 2–3 days and complete their life cycle in 20–30 days. Adult thrips feed on the flower bud, stem and leaf parts of the plant.

Hosts and symptoms

TSWV infects a variety of hosts, contributing to its global economic impact on crops. There are over a thousand different hosts for TSWV. The host range of TSWV includes agronomically important crops like

tomato The tomato is the edible berry of the plant ''Solanum lycopersicum'', commonly known as the tomato plant. The species originated in western South America, Mexico, and Central America. The Mexican Nahuatl word gave rise to the Spanish word ...

es and

tobacco Tobacco is the common name of several plants in the genus '' Nicotiana'' of the family Solanaceae, and the general term for any product prepared from the cured leaves of these plants. More than 70 species of tobacco are known, but the ...

. The symptoms of TSWV vary from host to host. There is also variability of symptoms within a single type of host due to the age of the plant, nutrition and the environment (especially temperature). Common symptoms include stunting, ringspots on fruit and

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. Necrosis is caused by factors external to the cell or tissue, such as infection, or trauma which result in the unregulated dige ...

of leaves. There are many different strains of TSWV, and differences in symptoms may also be attributed to the differences in the number of strains present.

Genome, phylogeny, and evolution

Tomato spotted wilt virus (TSWV) is a spherical

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 complementarity (molecular biology), complement in specifying a sequence of am ...

RNA virus that has a diameter between 80 and 110 nanometers. TSWV tripartite genome are named RNAs L (8.9 kb), M (4.8 kb), and S (2.9 kb). The RNA S has two genes which encode nucleocapsid (N) and nonstructural protein (NSs), respectively. p202/3WT, Tarquinia, and p105 isolates were always positioned in three different lineages according to phylogenetic analysis based on full genome, RdRp, GcGn, NSm, N, and NSs genes. TSWV isolates from worldwide shared high nucleotide and amino acid identities in N gene region. Additionally, the highly conserved N gene was found to be under very strong negative

selection pressures Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection. It is a quantitative description of the amount of ...

with estimated dN/dS values = 0.0638 and 0.0557.

Management

Prevention is key in managing TSWV. Once a plant becomes infected with TSWV, there are no practical ways to cure the virus infected plant. The most efficient method of containing this disease is genetic resistance. There are several different resistance

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

s identified in multiple crops. In some crops the resistance genes have been effective, however, in others, some strains of TSWV have been discovered to overcome the resistance gene, such as the ''Sw-5'' resistance gene in tomato. The ''Sw-5'' resistance gene in tomato is a dominant resistant gene. The ''Sw-5'' gene gives resistance to the ''TSWV'' through a hypersensitive response. A hypersensitive response is when the plant cells that surround the infection undergo cell death which would then deprive the virus of the cell machinery it needs to replicate and infect the plant further. There have been several strains of TSWV detected in countries such as

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...

and the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

that can overcome the ''Sw-5'' resistant gene. However, those strains of TSWV have not been spread worldwide so the ''Sw-5'' gene is still useful. Other important prevention techniques include buying virus and thrips-free transplants and managing thrips populations. Introducing species that naturally prey on thrips, such as the minute pirate bugs (''

Orius insidiosus ''Orius insidiosus'', common name the insidious flower bug, is a species of minute pirate bug, a predatory insect in the order Hemiptera (the true bugs). They are considered beneficial, as they feed on small pest arthropods and their eggs. They ...

'') and big eyed bugs (''

Geocoris punctipes ''Geocoris punctipes'', the big-eye bug, is a species of big-eyed bug in the family Geocoridae. It is found in the Caribbean, Central America, North America, Oceania Oceania (, , ) is a region, geographical region that includes Australasi ...

''), may help reduce transmission of TSWV. Insecticides are not an efficient way to decrease the vector population because the vectors rapidly develop resistance. Removing weeds and infected plants is a good way to prevent more infections in the greenhouse. Sanitation practices such as the destruction or removal of old crops by plowing or physical removal are often used in the field.

References

External links

* * {{Taxonbar, from=Q1706774, from2=Q24809119 Viral plant pathogens and diseases Tospoviridae