|Tobacco rattle virus|
|Electron micrograph of TRV particles in two types|
Tobacco rattle virus
Tobacco rattle virus (TRV) is a pathogenic plant virus. Over 400 species of plants from 50 families are susceptible to infection.
The virus causes the plant disease tobacco rattle in many plants, including many ornamental flowersincluding Narcissus . It causes the disease corky ringspot in potatoes. The disease manifests in various ways, and signs can include brown rings and arcs on the surface of a potato, and discolored spots on the interior.
Nematodes of the family Trichodoridae, the stubby-root nematodes, are vectors of the virus. The nematode species Paratrichodorus minor , for example, introduces the virus when it feeds on the roots of plants.The virus can also be spread on garden tools. It can also be mechanically and seed transmitted.
Boningfirst discovered Tobacco Rattle Virus in 1931 in Germany. It was discovered in Nicotiana tabacum, which is a species of cultivated tobacco.
Tobacco Rattle Virus is common and potentially serious in a variety of herbaceous ornamentals including, but not limited to, astilbe, bleeding heart, coral bells, daffodil, epimedium, gladiolus, hyacinth, marigold, tulip and vinca. Tobacco rattle can also affect vegetable crops such as beans, beets, peppers, potatoes, and spinach. On potatoes, the disease is referred to as corky ring spot. The disease corky ringspot of potatoes was first reported in the United States in 1946, and was identified incorrectly as a novel virus until advances in genetics demonstrated it to be the result of TRV.
Symptoms of Tobacco Rattle Virus vary based on the plant host, which differs widely in this disease. Common symptoms include mottling, chlorotic or necrotic local lesion, ringspots or line patterns, and systemic necrosis.
Tobacco Rattle Virus is a Tobravirus on plants. Transmission of Tobravirus is mostly supported by nematodes, such as Trichodorus and Paratrichodorus. These species of nematodes are known as stubby root nematodes.Transmission of the virus is separated into four distinct steps: Acquisition, absorption, retention, and virus particle release. At the beginning of the feeding cycle, the Stubby-Root Nematode punctures multiple individual cells by using its specialized stylet, an onchiostyle. Among those penetrated cells, the nematode select a cell which it will feed on. Upon selection, the nematodes begin sucking up cell contents, leading to death of the cell. During this process, adsorption of Tobravirus begins, the process where cytoplasm of infected cells containing Tobravirus is assimilated into the nematodes. Both juvenile and adult nematodes can pick up Tobravirus particles. Once the Tobravirus has been transferred into the nematodes, the retention portion of the lifecycle begins. Tobravirus consumed by the nematodes could linger in the nematodes for years. Eventually, the nematode loaded with Tobravirus starts its feeding cycle on uninfected root cell. During this period, Tobravirus will be transferred into the new cell, completing the virus transmission.
An Interesting feature of the life cycle of stubby root nematodes is that they reproduce in the absence of sexual activity. Because the nematode does not require sexual activity for reproduction, male nematodes are rarely detected. As a result, female nematodes lay eggs without sexual activity. The eggs hatch to begin the lifecycle of the nematode. Juvenile nematodes undergo molting three times until they reach the adult stage.Then, the life cycle begins again.
Tobacco Rattle Virus is dependent on the nematodes’ activity. Therefore, environmental factors that support nematodes’ movement or life cycle would lead to successful dispersal of this virus. One such environmental inducer is high soil moisture. Nematodes are obligate parasites; this means the nematode requires a host to survive. High soil moisture enables the nematodes to move more easily in the soil. With high soil moisture, nematodes also have better access to the root or root hairs, which enables them to easily transmit the pathogen on those cells.Moderately warm temperature allows faster life cycle of the nematode; If temperature were at optimum for nematode's life cycle, there would be a greater chance of dispersal of Tobravirus along the host plant.
Tobacco Rattle Virus can be managed through a variety of methods designed to make the environment unsuitable for transmission and viral propagation. Tubers or seeds of any susceptible plants should be purchased only from sellers certified as clean, and never planted in fields with a history of corky ringspot or Tobacco Rattle Virus-related disease. Many US states and several other countries run seed certification programs, for potatoes in particular.While its use requires a permit from many state or local governments, the nematicide 1,3-dichloropropene may be employed against fields overrun by stubby root nematodes, a common vector of the virus. Soil fumigants generally fail to penetrate the 40 inches necessary to ensure nematode eradication, and carbamates such as aldicarb and oxamyl are recommended as a last resort. Tobacco Rattle Virus is only found in nature in association with stubby root nematodes of genera Trichodorus and Paratrichodorus. Although otherwise considered harmless, they spread the infection during feedings. Nematodes may live and multiply within weeds in the field in between crop rotations, and it is advisable to employ non-host plants, such as alfalfa, to compete against weeds that may otherwise harbor the viral vector. In contrast, nightshade is a very problematic weed as it is an ideal host for the virus and the nematode. Growers can reduce symptom development by planting early and harvesting early. While the Russet Burbank cultivar proves to be highly susceptible to Tobacco Rattle Virus corky ringspot, Merrimack and several old European varieties exhibit resistance. Too much soil moisture can encourage nematode overpopulation, but tightly packed fine soil, clay, or sand can drastically inhibit the vector movement responsible for widespread and erratic field decimations. Once a plant is infected it cannot be treated and should be burned or disposed of as biohazard waste.
Tobacco Rattle Virus infects hundreds of plant species and is found in every continent where crops are grown.In the United States, it has been reported in Florida, Michigan, Wisconsin, Minnesota, Colorado, Idaho, Oregon, Washington, and California. Yet, no significant studies have been published examining the actual impact TRV leaves on agricultural sectors. Corky ringspot from TRV has been known to cut yields from 6-55 percent in the Pacific Northwest, rendering those affected crops unmarketable. Other than severe cosmetic damage to the tuber crops, however, corky ringspot disease from Tobacco Rattle Virus is not considered highly damaging to potato yields. TRV is commonly used in studies involving transgenic plants as a vector for silencing specified target genes. Thus, it is an important tool to plant physiologists and in the field of plant developmental genetics. Such research is important in creating "cross-protected" plants that are resistant or immune to the effects of the virus.
Plant pathology is the scientific study of diseases in plants caused by pathogens and environmental conditions. Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are ectoparasites like insects, mites, vertebrate, or other pests that affect plant health by eating plant tissues and causing injury that may admit plant pathogens. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
Plant viruses are viruses that affect plants. Like all other viruses, plant viruses are obligate intracellular parasites that do not have the molecular machinery to replicate without a host. Plant viruses can be pathogenic to vascular plants.
Root-knot nematodes are plant-parasitic nematodes from the genus Meloidogyne. They exist in soil in areas with hot climates or short winters. About 2000 plants worldwide are susceptible to infection by root-knot nematodes and they cause approximately 5% of global crop loss. Root-knot nematode larvae infect plant roots, causing the development of root-knot galls that drain the plant's photosynthate and nutrients. Infection of young plants may be lethal, while infection of mature plants causes decreased yield.
Spraing is a collective term for diseases and disorders of potato tubers that cause brown streaks in the flesh of the potato. Spraing can be caused by two viruses, tobacco rattle virus (TRV) which is transmitted by trichodorid nematodes, or Potato mop-top virus (PMTV) transmitted by the powdery scab fungus Spongospora subterranea. The two viruses may have synergistic effects in disease progression when both are present. Spraing like symptoms can also be caused by physiological defects or specific nutrient deficiencies, most notably Calcium.
This is a glossary of some of the terms used in phytopathology.
Nepovirus is a genus of viruses in the order Picornavirales, in the family Secoviridae, in the subfamily Comovirinae. Plants serve as natural hosts. There are 40 species in this genus. Nepoviruses, unlike the other two genera in the subfamily Comovirinae, are transmitted by nematodes.
Rotylenchulus reniformis, the reniform nematode, is a species of parasitic nematode of plants with a worldwide distribution in the tropical and subtropical regions.
Paratrichodorus minor is a species of nematode in the family Trichodoridae, the stubby-root nematodes. It occurs in tropical and subtropical regions of the world. It damages plants by feeding on the roots and it is a vector of plant viruses. It is a pest of some agricultural crops.
Meloidogyne javanica is a species of plant-pathogenic nematodes. It is one of the tropical root-knot nematodes and a major agricultural pest in many countries. It has many hosts. Meloidogyne javanica reproduces by obligatory mitotic parthenogenesis (apomixis).
Pratylenchus penetrans is a species of nematode in the genus Pratylenchus, the lesion nematodes. It occurs in temperate regions worldwide, regions between the subtropics and the polar circles. It is an animal that inhabits the roots of a wide variety of plants and results in necrotic lesions on the roots. Symptoms of P. penetrans make it hard to distinguish from other plant pathogens; only an assay of soil can conclusively diagnose a nematode problem in the field. P. penetrans is physically very similar to other nematode species, but is characterized by its highly distinctive mouthpiece. P. penetrans uses its highly modified mouth organs to rupture the outer surface of subterranean plant root structures. It will then enter into the root interior and feed on the plant tissue inside. P. penetrans is considered to be a crop parasite and farmers will often treat their soil with various pesticides in an attempt to eliminate the damage caused by an infestation. In doing this, farmers will also eliminate many of the beneficial soil fauna, which will lead to an overall degradation of soil quality in the future. Alternative, more environmentally sustainable methods to control P. penetrans populations may be possible in certain regions.
Xiphinema americanum, the American dagger nematode, is a species of plant pathogenic nematodes. It is one of many species that belongs to the genus Xiphinema. It was first described by N. A. Cobb in 1913, who found it on both sides of the United States on the roots of grass, corn, and citrus trees. Not only is Xiphinema americanum known to vector plant viruses, but also X. americanum has been referred to as "the most destructive plant parasitic nematode in America", and one of the four major nematode pests in the Southeastern United States.
Xiphinema diversicaudatum is an amphimictic ectoparasitic nematode species. This species has a characteristically long stylet capable of penetrating into a host's vascular tissue. They have a wide host range with some of the extensively studied ones being strawberry, hops and raspberry, due to their economic importance. The direct root damage caused through penetration near the root tip and formation of galls is a secondary concern when compared with the damage caused by vectoring the Arabis mosaic virus. The virus attaches to the interior cuticle lining and can be transferred from infected to uninfected root tissue as the nematode feeds and sheds. Management of this particular nematode relies on nematicides such as 1,3-Dichloropropene (Telone) at 40 gpa.or methyl bromide at 1000 lb/ac to control to 28 in deep.
Xiphinema index, the California dagger nematode, is a species of plant-parasitic nematodes.
Tobacco ringspot virus (TRSV) is a plant pathogenic virus in the plant virus family Secoviridae. It is the type species of the genus Nepovirus. Nepoviruses are transmitted between plants by nematodes, thrips, mites, grasshoppers, and flea beetles. TRSV is also easily transmitted by sap inoculation and transmission in seeds has been reported. In recent cases it has also been shown to appear in bees, but no transmission to plants from bees has been noted.
Tobravirus is a genus of viruses, in the family Virgaviridae. Plants serve as natural hosts. There are three species in this genus. Diseases associated with this genus include: SBWMV: green and yellow mosaic.
The nematodesroundworms or eelworms, constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a broad range of environments. Most species are free-living, feeding on microorganisms, but there are many that are parasitic. The parasitic worms (helminths) are the cause of soil-transmitted helminthiases.
Paratrichodorus is a genus of terrestrial root feeding (stubby-root) nematodes in the Trichodoridae family (trichorids), being one of five genera. They are economically important plant parasites and virus vectors. The females are didelphic, and are distributed worldwide.
Trichodoridae is a family of terrestrial root feeding nematodes, being one of two that constitute suborder Triplonchida. They are economically important plant parasites and virus vectors.
Trichodorus is a genus of terrestrial root feeding (stubby-root) nematodes in the Trichodoridae family (trichorids), being one of five genera. They are economically important plant parasites and virus vectors.
Cocoa necrosis virus (CoNV) is a plant pathogenic virus of the genus nepovirus that infects Theobroma cacao en natura causing cacao necrosis disease. CoNV is considered synonymous with Strain S of cacao swollen shoot virus. Unlike Cacao swollen shoot virus, it is not transmitted by mealybugs nor vectored by aphids, beetles, or leafhoppers that also commonly infest cacao. It is serologically, distantly related to Tomato black ring virus and very distantly related to Grapevine chrome mosaic virus.