TRANSMISSION AND CONTROL MEASURES OF PLANTVIRUSES

Compiled by Dr. Rukhshana Parveen

Assistant Professor, Department of Botany Gautum Buddha Mahila College, Gaya

Magadh University, Bodhgaya

Pathology is derived from two Greek words Pathos= suffering and logos= discourse or to speak.

Plant Pathology is a discourse on the suffering plants. The field of plant pathology comprises both the art of treating the sick plant and the science of understanding the nature of the diseased plant.

The first observations on plant diseases by Theophrastus, 300 B.C.

The first book on plant pathology by Juleus Kuhn (1858 A.D.) J.C. Horsfall and A.E. Diamond (1959) have concluded that ‘disease is a

malfunctioning process that is caused by continuous irritation. The viruses which infect plants are called Plant Virus. Virus moves from one host to another for its survival. Transmission of virus is dependent on external carrier.

Some common mode of transmission of plant viruses are :-

1. Transmission by vegetative Propagation. Plants which are propagated vegetatively once infected with virus disease transmit the

pathogen from one generation to the next. Virus may be transmitted by tuber, corms, and bulbs, grafting and cutting. Example Potato Spindle Tuber Viroid (PSTV)

1. Potato Spindle Tuber Viroid (PSTV)

2. Transmission by Friction and Rubbing. When leaves of closely growing infected and healthy plants rub together, the healthy

plants get infected.

Also transmitted by contact of infected leaves with clothes of men and bodies of animals

Example : - Potato Virus X (PVX) and Tobacco mosaic Virus(TMV)

2. Potato Virus X 3. TMV

3. Transmission Through Alternate Host:- Virus causing Yellow Vein Mosaic of Bhindi and Cucurbit Mosaic are transmitted

through alternate or collateral hosts.

4. Transmission through soil Virus spread through soil so, called as Soil Borne Virus. Virus enter host through roots by mechanical or biological methods. Example: TMV

4. Transmission by Soil

5. Transmission by Seeds:- Virus particles present within the seed tissues, the seedling produced from such seeds

are naturally infected by the virus.

5. Seed Transmission

Example: Ring Spot Virus in Soybean, Mosaic Virus in Watermelon, Strip Mosaic Virus in Barley and Curly Top Virus of Beet sugar

6. Transmission by Pollen grains:- Flowers of healthy plants are pollinated with the pollens from infected plants. When seed are formed they carry virus.

6. Transmission by Pollen grains

Example: Stone Fruit Ring Spot Virus in Squash and sour curry, Yellow Virus in sourCheery and Bean Mosaic Virus

7. Transmission through Fungi:- TMV is transmitted by root infecting fungus. Synchytrium endobioticum transmit Potato Virus X. Polymyxa graminis transmit Wheat Mosaic Virus. Olpidium brassicae transmit Tobacco Necrosis lettuce big vein and Tobacco Stunt

Virus.

8. Transmission by Infected agricultural tools:- Common method of virus transmission. Virus gets stuck to the implements used for cutting, pruning, weeding of infected crop

and when these tools are used for healthy plant virus are transmitted.

7. Transmission by infected agricultural tools

Exampl : Potato Virus X, TMV and Leaf Mosaic of Cucurbits.

9. Transmission by Arthropod Vectors:-

A variety of arthropods are known to serve as natural vehicles or vectors of plant virus.

Aphids => Largest group of insect vectors.

Example: Pea Enation Mosaic Virus, Potato Virus Y transmitted by Myzus persicae

8. Myzus persicae

Leaf Hopper and Plant Hopper=> Transmit semi-persistent and persistent virus to herbs and shrubs.

Example: Rice Dwarf Virus is transmitted by nymphs of Nephotettix cincticeps.

9. Nephotettix cincticeps

White Flies=> Present in large number s on the underside of leaves. During feeding these acquire the virus. Example : Abutilon Mosaic is transmitted by Bemisia tobaci and Tobacco leaf curl transmitted by Aleurotrachelus socialis

10. Bemisia tobaci 11. Aleurotrachelus socialis Bugs and Thrips => Bugs are responsible for the transmission of Cacao Swollen

Shoot Virus.Tomato Ring Spot Virus is transmitted by nymphs of Thrips tobaci

12. Bugs 13. Thrips

Beetles=> Beetles are chewing insects and transmit virus regurgitation of sap from the fore gut.

Example: Cowpea Mosaic is transmitted by Ceratoma trifurcate and Turnip Yellow Mosaic is transmitted by Phyllotreta sp.

14. Beetle

Mites=> these are related to spiders which feed by sucking the contents from the plants.

Example: Potato Virus Y is transmitted by Tetranychus urticae and Wheat Streak Mosaic transmitted by Aceria tulipae

15. Mites

11.Transmission by Nematodes=> Nematode vectors transmit viruses by feeding on roots of infected plants and then

moving on to roots of healthy plants. Four genera of Nematodes transmit plant virus. These are Xiphinema, Longidocus,

Trichodorus and Paratrichodorus.

16. Nematode

12.Transmission with Dodder=> Parasitic plant called Dodder transmits many plant virus. Example : Cucumber Mosaic Virus is easily transmitted with Dodder

17. Dodder (Cuscuta)

Control Measure of Plant Virus

T.S. Ramakrishnan (1961) state that” Diseases exact a heavy toll of crop yields and cause considerable damage to year after year”.

Diverse methods have been adopted from time to time to mitigate the ravages caused by these diseases.

Control measures divide into two groups.

1. Prophylaxis: - Protection of the host from exposure to the pathogen from infection.Divided into three groups:-

Exclusion of the Parasite:Measures are designed to keep the pathogen away from entering the area in which the host is growing. These include quarantine regulation, inspection and certification.

Eradication of the Parasite: Elimination of insect- Plants may be protected against Crop Rotation – If the susceptible host plants are not available for 2 to 3

years, naturally the nematodes will die. The crop rotation must be done with nonhost plants.

Removal of Infected Parts- The destruction of diseased parts of plants in the field removes the main foci of infection and thus breaks the chain. Citrus Canker can be effectively controlled by the removal of affected plant parts.

Elimination of Alternate Hosts – In some of the destructive diseases in which long cycled, heteroecious rust fungi are concerned, the eradication of alternate host is a possible means of control. Example- Crown Rust of Oat

Destruction of Wild Host and Weed- A large number of diseases is harboured in wild hosts and weed. Removal of such wild hosts is a good method of control. Exampl-Yellow Vein Mosaic of Bhindi persists on wild host Hibiscus tetraphylus.

Rogueing – This practice consists of destruction of affected plants from the fields at an early stage by removing foci of infection and preventing wide dissemination of the pathogen. Example- Yellow Vein Mosaic of Bhindi andKatte disease of cardamom

Improved cultural Practices Raising of beds- The Foot Rot of Ginger caused by Pythium

myriotylum occurs in low bed areas. By planting the crops on raised beds has removed those conditions which favoured the pathogen.

Change in planting season- The Leaf Rust of Sugarcane and Blast of Ragi have been controlled by this method that planting these crops during September – October instead of in June- July. It is a case of disease escape.

Obtaining seeds from disease free localities- The Foot Rot of Ginger caused by Pythium myriotylum is prevalent in South India, this can be controlled by importing seed rhizome from disease free arid zone of Northern India

Proper manuring- Application of balanced dose of nitrogen help in the reduction of Blast and Leaf Spot of Rice.

Soil hygiene – Field sanitation is an important factor in the healthy andvigorous growth of plants.

Mixed cropping- The practice of mixed cropping has helped effectively the spread of infectious disease.

Amendment of soil conditions- Amendment of factors like soil moisture, soil texture, soil pH etc.

Soil sterilization- The soil may be sterilized completely or partially, where not all the organism is destroyed, but only certain groups. Soil (15-20 pounds)is heated under pressure 2-3 hours.

Biological control – Concept of biological control is given by Baker and Cook (1974). Some of the methods of biological control are Antagonism (Amensalism, competition, parasitism and predation), Nematophagy, Mycophagy etc.

Direct Protection Use of Fungicides – The application of fungicide to the host surface prevents

the germination of spores or kill the germ tube before they enter the host tissue. A good should be toxic to the parasite and not to the host. Example- Bordeaux mixture, Perenox, Fungimar, Cuprous oxide, Copper oxychloride,

Insoluble copper, Suplhur and sulphur compound Phelam, Sulpham, Agallol, Captan, Thiram, Zineb, Dichlone etc.

Use of Fumigants- Example Chloropicrin, Carbon disulphide, Chloeobromopropene etc.

Antibiotic-The antibiotic are those substances which are produced by one microorganism and become toxic to other microorganism. Example- Streptomycin, Tetracyclines, Cyclohexmide, Griseofulvin etc.

Use of Growth regulators- Some plants harmones have been reported to reduce infection of plants by certain pathogen.

2. Immunization or disease resistance: - Implies improvement of resistance of the hostto infection.

Resistant Varieties- To sow the resistant varieties is the simplest and cheapest method of control.

Photographs were taken from Google.

Books Cited: -

1. Saxena, R.S. 2018. Text Book B.Sc. Botany-1.2. Dubey, R.C. and Maheshwari, D.K. 1999. Text Book of Microbiology.3. Pandey, B.P. 1982. Plant Pathology.4. Singh, V., Pande, S.N. and Jain 2010. Text Book of Botany.