Tomato black ring virus: Difference between revisions

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===Description and Significance===
===Description and Significance===


Tomato Black Ring Virus (TBRV) is a RNA-containing virus that occurs in Europe. It infects a wide range of herbaceous and wood monocotyledonous and dicotyledonous species including many that are important crop plants. It appears on these plants as necrotic rings, spots and flecks, systemic chlorotic ringspots, mottle, stunting, leag malformationa and vein yellowing.<sup>1</sup> In addition to black ring of tomato, the various strains of this virus cause ringspot diseases of bean, sugarbeet, lettuce, raspberry and strawberry, yellow vein of celery,shoot-stunting of peach and unnamed diseases of leek and onion. It occurs in many other plants, including cabbage, grapevine and lucerne. Plants infected with TBRV are patchily distributed in crops because of slow migration of the soil-inhabiting vectors, Longidorus spp. Some strains tend to occur in soils together with strains of raspberry ringspot virus because they share the vector L. elongatus.
Tomato Black Ring Virus (TBRV) is a RNA-containing virus that occurs in Europe. It infects a wide range of herbaceous and wood monocotyledonous and dicotyledonous species including many that are important crop plants. It appears on these plants as necrotic rings, spots and flecks, systemic chlorotic ringspots, mottle, stunting, leag malformationa and vein yellowing.<sup>1</sup> In addition to black ring of tomato, the various strains of this virus cause ringspot diseases of bean, sugarbeet, lettuce, raspberry and strawberry, yellow vein of celery,shoot-stunting of peach and unnamed diseases of leek and onion. It occurs in many other plants, including cabbage, grapevine and lucerne. Plants infected with TBRV are patchily distributed in crops because of slow migration of the soil-inhabiting vectors, Longidorus spp. Some strains tend to occur in soils together with strains of raspberry ringspot virus because they share the vector L. elongatus.<sup>2</sup>


==Genome structure==
==Genome structure==

Revision as of 01:23, 19 December 2008

A Microbial Biorealm page on the genus Tomato black ring virus

Classification

Higher order taxa

Virus; ssRNA viruses; ssRNA positive-strand viruses, no DNA stage; Picornavirales; Comoviridae; Nepovirus; Subgroup B

Description and Significance

Tomato Black Ring Virus (TBRV) is a RNA-containing virus that occurs in Europe. It infects a wide range of herbaceous and wood monocotyledonous and dicotyledonous species including many that are important crop plants. It appears on these plants as necrotic rings, spots and flecks, systemic chlorotic ringspots, mottle, stunting, leag malformationa and vein yellowing.1 In addition to black ring of tomato, the various strains of this virus cause ringspot diseases of bean, sugarbeet, lettuce, raspberry and strawberry, yellow vein of celery,shoot-stunting of peach and unnamed diseases of leek and onion. It occurs in many other plants, including cabbage, grapevine and lucerne. Plants infected with TBRV are patchily distributed in crops because of slow migration of the soil-inhabiting vectors, Longidorus spp. Some strains tend to occur in soils together with strains of raspberry ringspot virus because they share the vector L. elongatus.2

Genome structure

The TBRV has isometric particles between 26 to 30 nm in diameter with hexagonal outlines. In purified preparations, particles exist as three sedimenting components with sedimentation coefficients (S20,w) of 55S, 97S and 121S, termed T, M and B, respectively. All particles consist of 60 protein subunits each of molecular weight 57 000 but, whereas T particles are nucleic acid-free protein shells, M and B particles contain linear ssRNA with molecular weight of 1.7 x 10^6 and 2.7 x 10^6, respectively. Some virus isolates contain in addition a satellite RNA of molecular weight 0.5 x 10^6. Several different satellites have been described for different TBRV isolates.

The complete sequence genome for TBRV RNA1 and RNA 2 has been sequenced. The sequence of TBRV RNA 1 is 7356 nucleotides long. A putative initiation codon at nucleotide 261 was considered to be the start of an open reading frame which terminates at a UAG codon at position 7053. The sequence of TBRV RNA 2 is 4618 nucleotides long and contains an open reading frame endcoding a polypeptide of 1344 amino acids.

Cell structure and metabolism

Interesting features of cell structure; how it gains energy; what important molecules it produces.

Virions consist of a capsid. The virus capsid is not enveloped and is round with icosahedral symmetry. These capsids appear hexagonal in outline and the capsomer arrangement is not ovbious.

In 2 distantly serologically related isolates (A and G12) of TBRV that each produce 2 RNA species, RNA-1 is found only in bottom component (B) particles and RNA-2 is found only in middle component (M) particles. Preparations of separated M and B particles are barely infective, but produce 8 to 30 times more lesions when mixed. This indicates that both kinds of particle are needed for infection because they contain different parts of the genome. Infectivity is not enhanced when M particles of isolate G12 are mixed with B particles of isolate A, but it increases when M particles of isolate A are mixed with B particles of isolate G12. The lesions produced are abnormally small; isolates cultured from some of them are slower than the parental isolates to produce systemic symptoms in Chenopodium quinoa and have serological properties indicating that their coat protein cistron is in RNA-2.

Ecology

The virus can best be detected in all parts of the host plant and particularly in the mesophyll. Virions are found in the cytoplasm, cell vacuole (tubules extending through plasmodesmata, which is possibly a sign of degenerating nuclei).

The two types of RNA present in TBRV are both genomic RNA species and are necessary for infectivity. Natural transmission between plants is by vector nematodes of the dorylaimid genus Longidorus: L. attenuatus and L. elongatus. Larvae and adults are able to transmit but the virus is not retained after moulting, nor is it passed to progeny through the egg. Nematodes acquire virus from infected plants after feeding for about 1 hour and retain the ability to transmit for many weeks in soil without host plants. Different TBRV isolates often have different vector species. Thus, in the UK, isolates of TBRV from Scotland are transmitted most efficiently by L. elongatus, whilst those in England (and also on the mainland of Europe) are transmitted largely by L. attenuatus.

The virus is also transmitted through seeds of infected plants, often with a high frequency, especially in some crop species and weeds. This enables the virus to be dispersed over a wide area. Additionally, the virus can be dispersed by transport of soil containing TBRV-infected nematodes and/or TBRV-infected seed. In perennial plants, virus may be distributed in material vegetatively propagated from infected plants.

TBRV can cause severe disease in some raspberry, strawberry and peach cultivars in some localities but the incidence of such infections is often small. Yield loss in crops is difficult to quantify but, although significant in some cultivars of some crops, it is probably of only local importance.

Pathology

Infected weed and crop plants may show few or no symptoms especially in the year of infection or when infection occurs throught he seed. Nevertheless, plant growth in such plants may be impaired. Where infection occurs through nematode transmission, this often appears as patches of poor growth which slowly extend in size each year. Depending on the cultivar, natural infection in Rubus and Fragaria may induce chlorotic mottling and/or ringspots in leaves. In potato, leaves may develop black necrotic spots. In celery, Sambucus nigra and some other shrubs, leaves may show bright-yellow vein-clearing. Symptoms are generally most obvious in plants in early spring growth and are less noticeable during more rapid growth in summer. TBRV is readily transmitted by inoculation of sap to many herbaceous test plants but mechanical inoculation of virus from woody plants should be made in 2% (v/v) nicotine sulfate (pH 9.3). In test species such as Chenopodium quinoa, C. amaranticolor and Nicotiana clevelandii, TBRV induces chlorotic or necrotic local lesions and systemic necrosis, depending on the virus isolate. Such symptoms, although indicative of virus infection, are not diagnostic for TBRV, and other tests, such as serology or nucleic acid hybridization, are necessary to establish unequivocally the presence of TBRV. Serological tests are generally the most convenient and ELISA is probably the most sensitive. However, because of the serological variability of TBRV isolates, antisera to each of the two main serotype groups should be used. ELISA has been successfully used to detect TBRV directly in plants such as grapevine, raspberry and strawberry.

Current Research

Enter summarries of the most rescent research here--at least three required

References

[Sample reference] Takai, K., Sugai, A., Itoh, T., and Horikoshi, K. "Palaeococcus ferrophilus gen. nov., sp. nov., a barophilic, hyperthermophilic archaeon from a deep-sea hydrothermal vent chimney". International Journal of Systematic and Evolutionary Microbiology. 2000. Volume 50. p. 489-500.

Edited by student of Emily Lilly at University of Massachusetts Dartmouth.