virus vector relationship & mites as vectors of plant diseases

VIRUS VECTOR VIRUS VECTOR RELATIONSHIPRELATIONSHIP&&

MITES AS VECTORS OF MITES AS VECTORS OF PLANT DISEASESPLANT DISEASES

VIRUS VECTOR VIRUS VECTOR RELATIONSHIPRELATIONSHIP&&

MITES AS VECTORS OF MITES AS VECTORS OF PLANT DISEASESPLANT DISEASES

S.KALIYAMOORTHY08-602-006

Viruses

"Noncellular, sub microscopic, obligatory intracellular parasites composed of a proteinaceous covering around central nucleic acid (either DNA or RNA) and capable of self- replication within the living host cells."

vector

An organism, usually an insect, that carries and/or transmits disease causing viruses.

FACTS of Transmission of Plant Viruses

• Plant viruses do not penetrate the intact plant cuticle.

• Not disseminated as such by wind or water, and even when they are carried in plant sap or debris

• Generally do not cause infections unless they come in contact with the contents of wounded living cell

1. Mechanical contact2. Grafting3. Vegetative propagation4. Botanical (sexual) seed5. Pollen6. Common dodder(Cuscuta sp.)7. Vectors

Virus-Vector Relationship

During feeding and transmission, there is a relationship is established between the vector and the virus which is referred to as

‘virus-vector relationship’.

Classification of Plant Viruses

1. Tobravirus group2. Tobamovirus group3. Potexvirus group 4. Carlavirus group5. Potyvirus group6. Cucumovirus group7. Tymovirus group8. Comovirus group

9. Nepovirus group10. Bromovirus group11. Tombusvirus group12. Caulimovirus group13. Alfalfa mosaic virus14. Pea enation mosaic virus15. Tobacco necrosis virus16. Tomato spotted wilt virus

Monotypic groups Harrison et. al, 1971

Definitions • Acquisition access period (AAP):

The period of time given for the vector to acquire the virus.

• Inoculation access period (IAP): The period of time given for the vector to transmit the virus

• Retention: The length of time after virus acquisition that the vector remains viruliferous

Contd..,

• Latent period:• Time interval between the AAP & the vector

become viruliferous.

Terminologies

(l) Stylet-borne viruses (non-persistent)(2) Circulative viruses (semi-persistent)(3) Propagative viruses (persistent)

Stylet-borne viruses.

• Transmitted by aphids. • The acquisition period : few minutes to many hours and during this

period they remain 'viruliferous'. • After transmitting the viruses, aphids become virus-free or

'aviruliferous'. • 'Non-persistent' viruses. • Transmission : mechanical process. • Induce mosaic symptoms & saptransmissible.• Cucumoviruses, carlaviruses and potyviruses• Few stylet-borne viruses can only be transmitted by a particular vector. – Myzus ornatus -cauliflower mosaic virus and M. ascolonicus -cucumber mosaic virus

Light micrograph of a LS through an aphid head and leaf

(A)The aphid stylet protrudes from the proboscis

(B) Penetrates intracellularly through the mesophyll cells.

(C) penetrates into the vascular bundle.

stylets of Myzus persicae given acquisition access to 125I-labeled tobacco etch potyvirus

virionsStylets of an aphid that has not fedon an infected plant

Stylets of an aphid that acquired labeled virus through a plastic membrane.

• Distribution of label in stylets that have separated, showing label associated only with the food canal formed by the maxillary stylets

Circulative viruses

• Circulate through the tissues of the vectors• Not transmitted immediately after the

acquisition but the vectors have to wait several hours

• 'semi-persistent' viruses. • Circulative viruses are mainly transmitted by

aphids. • Maize chlorotic dwarf virus, • rice tungro virus, • pea enation mosaic virus, • potato leaf-roll virus, • lettuce mosaic yellow virus etc.

Circulative route of barley yellow dwarf luteoviruses (BYDVs)

through aphids.

Propagative viruses

• viruses start multiplying within their vectors and establish a biological relationship.

• viruses possess an incubation period(To Reach Specific Conc) • Four aphid-transmitted viruses and almost all

leafhopper transmitted viruses are propagative. • Vector remain viruliferous throughout their life• 'Persistent' viruses.

• Wheat striate mosaic virus, • TSWV• potato yellow dwarf virus, • rice dwarf virus etc.

conclusion

• Virus-vector relationship Idea about type of transmission.

• Type of transmission decision of control measures.

References

• Annual Review of Phytopathology Vol. 44: 183-212 (2006)

• MICROBIOLOGY AND MOLECULAR BIOLOGY REVIEWS, 1999, p. 128–148 Vol. 63, No. 1.

• Advances in Virus Research By Karl Maramorosch, Kenneth Manley Smith, Max A. Lauffer

• http://arab2000.forumpro.fr

Mite transmission of plant diseases

• Black currant reversion disease by Cecidophyopsis ribis (Amos et al. 1927)

• Eriophyidae – major role in transmission of plant diseases.

Eriophyid mites as vectors of plant diseases

• Extremely small(150µ-225µ length).• Living in concealed places• Spread through the drift.• very less chance of spread & multiplication

off virus in the ecosystem.

Virus transmission by Eriophyid mites

1. Currant reversion virus2. Fig mosaic virus3. Peach mosaic virus

1. Wheat streak mosaic virus2. Wheat spot mosaic virus3. Ryegrass mosaic virus

Infect only woody plants &Artificial transmission by grafting

Infect only grasses

Manual transmission by leaf rubbing

Currant reversion virus(CRV) Cecidophyopsis ribis

• First evidence (Amos et al. 1927).• Massee 1952 confirmed the transmission by

mites• Reversion- characteristic change of leaves

and bushes.

Wheat streak mosaic virus (WSMV)Aceria tulipae

• First reported in Kansas 1932• Serious and widely distributed disease of

winter wheat.• also occurs on spring wheat and barley, corn,

rye, oats, and a number of annual and perennial grasses

• Damage to winter wheat is most severe.

Symptoms• Blotches and discontinuous dashes In leaves

or streaks that are light green to a yellow.• These areas are parallel to the veins• Later leaves show a general yellow mottling

symptom.• Infected plants tend to spread out more than

normal ones, frequently developing an abnormally large number of tillers.

• Partial sterility and shriveled kernels.

Only young (nymphal) mites can acquire the virus. 15 min AFPNo transovarial transmissionMites become aviruliferous after 7-9 days.

Wheat spot mosaic virus(WSpMV )Aceria tulipae

• Aceria tulipae proved as vector – 1956 by slykhuis.

• Frequently associated with WSMV• Chlorotic spots on the leaves.• Except egg stage all the stages can transmit

virus .

Fig mosaic virus (FMV) Aceria fici

• Different patterns of chlorotic to yellowish mottling and deformation of leaves .

• Leaves and fruits may be dwarfed and some leaves may be malformed.

• On leaves, mosaic spots will appear yellow and may cover large areas of the leaf.

• In some cultivars, premature defoliation and fruit drop can occur.

• A. greenhouse-grown rooted cutting from a FMD-affected Mexican fig accession

• B. A group of double-membrane bodies (DMB) in a parenchyma cell

• C. Very flexuous filamentous particles (V)

• D. semi-rigid virus-like particles (V) surrounding chloroplasts (Ch) in a parenchyma cell.

Castellano et al. 2007

Peach mosaic virus (PMV) Eriophyes insidiosus

• Reported at Texas by Hutchins in 1932

Symptoms:

• Shortening of internodes.• Profuse growth in leaf axil buds.• Mosaic pattern on leaves.

Ryegrass mosaic virus (RMV)Abacarus hystrix

• In 1958 Abacarus hystrix –identified as vector.

• Light green to yellow colour spots or streaks on the leaf.

• virus causes pale green streaks in the leaf lamina and in severe cases, the leaf may show yellow flecking which is followed by necrosis and death of the tiller

Pigeonpea sterility mosaic virus (PPSMV) Aceria cajani

• Chlorotic patches on leaf.• Reduction in leaf size.• SMD inhibits flower production and renders

plants sterile.• Early infection leads to complete sterility.• Later stage : sterility in some branches only.

Cherry mottle leaf virus Eriophyes inaequalis

• Terminal leaves develop irregular chlorotic mottle and distortion.

• Puckering, shot-hole on the leaf. • Reduced leaf size.• Dieback of shoot ends and leaf fall does not

occur.• Infected trees can appear rosetted.• Delayed ripening of fruits.

James 1992

Cadang-cadang disease( CCCVd) Notostra antennuata

Early stage (lasting 2-4 years):– Yellow leaf spots appearing water-soaked in reflected

light

Medium stage:– Leaf spots become numerous– Lower two-thirds of the crown a yellowish appearance.– Inflorescences become necrotic, infertile and nut

production ceases.– Frond production and size decline.

Contd..,Late stage (>5 years):

Whole crown yellow/bronze-coloured .

Reduced in size and number of fronds.

Leaflets become brittle and palm dies.

Time from appearance of first symptoms to tree death ranges from around 8 to 16 years and is generally greater in older palms

Mango malformationAceria mangiferae

Tetranichid mites as vectors of plant diseases

• Spider mites- able to spin web over the leaves.

• Colour: yellow to greenish & orange to red.

• 8 legged, medium sized(0.8mm) and pear oval shaped body.

Potato virus YTetrnychus urticae

•Mottling in top leaf later spread to older leaf.

•Stunted plant growth.

•Shortening of internode

•Plant become resorted appeareance

Mosaic disease in wheat, corn and rye Tetranychus sinhai

• Yellowing and withering of plants.

• Yellow patches along the midrib

References• Advances in Virus Research By Karl Maramorosch,

Kenneth Manley Smith, Max A. Lauffer• Annual Review of Entomology1970:

Vol. 15: 343-380• Journal of Plant Pathology (2007), 89 (3), 441-444• J. gen. Virol. (I973), I8, 4o9-4II• Annals of Applied Biology Volume 48 Issue

3, Pages 575 - 579• Indian Journal of Virology Year : 2005, Volume : 16,

Issue : 1and2• Egypt . J . phytopathol., Vol. 30, 2(2002)