Viruses are obligate parasites that need a living host for their growth and multiplication. Viruses enter plant cells through wounds usually made mechanically or by vectors. Viral diseases are a significant cause of crop loss in India, affecting crops such as rice, wheat, maize, sugarcane, tomato and potato, among others. Viral infections cause a yield loss of about 70-80% and in severe cases, up to 90-100% depending upon factors like severity of disease, source of infection, duration of infection and environmental conditions.

The symptoms of viral diseases in plants vary depending on the virus and the host plant. The most common symptoms include stunted growth, yellowing of leaves, mottling or streaking of leaves, necrosis, distorted leaves or flowers, wilting and reduced yield. Therefore, proper plant disease management is essential to protect crop health and yield.

Transmission of Viral Diseases in Plant:

Plant viruses are transmitted through various sources from an infected plant to a healthy plant.

1. Vegetative Propagation

When vegetative parts like tubers, bulbs, cuttings or rhizomes of the infected plants are used as mother plants for propagation, the new plant raised will also be infected by the viral disease.

2. Seeds

Seeds can be a source of viral infection in plants. Seeds can be affected by viruses through contaminated soil or water. Virus-infected seeds can transmit the virus to plants, resulting in a new generation of infected plants that can further spread the disease through insect vectors, contaminated soil, water, etc.

3. Mechanical transmission

Mechanical transmission occurs when the virus is physically transmitted from one plant to another by rubbing of sap, through contact with contaminated tools and equipment or through human handling during intercultural practices.

4. Pollen transmission

When a pollinator or the wind comes across an infected plant and collects pollen, the virus can be transferred from one plant to another.

5. Insect transmission

Plant viruses can also be spread through insect transmission, also known as vector transmission. Insects such as aphids, whiteflies, leaf hoppers and thrips are common vectors for many plant viruses. Other than this, nematodes and mites also act as vectors for viral infection.

Major Viral Diseases in Plants:

1. Tobacco Mosaic Virus:

Host range - Tobacco, Potato, Brinjal, Pepper, Cucumber

Transmitted by - Sap, contaminated farm equipments, soil debris, hands of farm labours

Symptoms - Mottling pattern of light and dark green patches on the leaf lamina, stunted growth, development of blisters/irregular crumbled swellings on leaves, small and misshapen infected leaves.

2. Cauliflower Mosaic Virus (CaMV)

Host range - Tomato, Melons, Squash, Beet, Spinach, Broccoli, Cabbage

Vector - Aphids

Symptoms - Mosaic patterns on affected leaves, young leaves become twisted leading to stunted growth.

3. Sugarcane Mosaic Virus

Host range - Sugarcane

Vector - Aphids

Transmitted by - Infected canes used as seed/sett

Symptoms - Yellowish/Chlorotic stripes with alternate normal green portion of the leaf, stunted growth.

4. Maize Mosaic Virus

Host range - Maize

Vector - Leaf hopper

Symptoms - Chlorotic stripes and spots on leaf, leaf sheath, stalks & husks, moderate to severe rosette formation on new growth.

5. Cucumber Mosaic virus (CMV)

Host range - Cucumbers, Tomato, Pepper, Squash, Melons, Beans, Peas, Spinach, Beetroot, Lettuce, Radish

Vector - Aphids

Symptoms - Mosaic patterns, stunted growth, distortion of leaves, yellowing of veins, necrotic spots or streaks on infected leaves.

6. Groundnut Bud Necrosis

Host range - Groundnut, Tomato, Green gram

Vector - Thrips

Symptoms - Mottling or chlorotic spots on leaves, necrosis of terminal bud, distortion of lamina, reduction in leaflet size, reduced flowering, production of abnormally small and wrinkled seeds.

7. Leaf Curl Virus

Host range - Tobacco, Cotton, Papaya, Guava, Chilli, Tomato

Vector - Whitefly

Symptoms - Stunted growth due to reduced nodes and internodes size, curling of leaf margins upward and downward, thickening of veins, crinkling and distortion of leaves.

8. Vein Clearing / Yellow vein Mosaic

Host range - Bhendi

Vector - Whitefly

Symptoms - Yellowing of veins in the leaf blade, reduced size of younger leaves and stunted growth, flowering and fruiting are restricted, if formed are small and hard.

9. Rice Tungro Virus

Host range - Paddy

Vector - Leaf hopper

Symptoms - Stunted growth, yellow to orange discoloration of leaves, interveinal chlorosis, reduced tillering with poor root system.

10. Tomato Spotted Wilt Virus

Host range - Tomato

Vector - Thrips

Symptoms - Appearance of streaks on leaves, stems and fruits. Leaves have small, dark, circular spots and may have bronzed appearance. Numerous concentric circular markings on fruits. Ripe fruits show alternate red and yellow markings.

11. Papaya Ringspot Mosaic Virus

Host range - Papaya, Guava

Vector - Aphids

Symptoms - Vein clearing, leaf margin roll downwards and inwards, mottling patterns, dark green blisters, fruits having circular concentric rings on them, stunted growth.

12. Sterility Mosaic

Host range - Red gram

Vector - Eriophyid mite

Symptoms - Bushy and pale green appearance of affected plants, excessive vegetative growth, mosaic pattern on leaves, reduction in leaf size, stunted growth, complete or partial termination of flowering leading to sterility.

13. Bunchy Top Virus

Host range - Banana

Vector - Aphids

Transmitted by - Infected suckers (Primary source of infection)

Symptoms - Stunted plant growth, reduction in leaf size, leaf marginal chlorosis and curling, leaves crowded at the top giving “bunchy top” appearance and smaller branch size.

14. Potato Leafroll Virus

Host range - Potato, Tomato, Capsicum

Vector - Aphids

Symptoms - Stunted growth, chlorotic spots, mottling patterns, leaves roll upwards, upright orientation of leaves.

15. Citrus Tristeza Virus

Host range - Citrus

Vector - Aphids

Symptoms - Development of deficiency symptoms on leaves, dieback of twigs, decay of roots, and reduced fruit set.

16. Grassy Stunt Virus

Host range - Paddy

Vector - Brown Plant Hopper

Symptoms - Stunted plant growth with excessive tillering, pale green leaves with rusty spots, grassy and rosette appearance of plants.

17. Ragged Stunt Virus

Host range - Paddy

Vector - Brown Plant Hopper

Symptoms - Dark green leaves with spiky or serrated edges, leaf edges are twisted into spirals, giving a ragged appearance, stunted plant growth, delayed flowering, and incomplete panicle emergence.

18. Mungbean Yellow Mosaic Virus

Host range - Black gram, Green gram, Moth bean, Soybean, Cow pea

Vector - Whitefly

Symptoms - Stunted growth, yellowing, presence of mosaic patterns, delayed maturity, reduced flower and pod formation; if produced, pods would be small and distorted.

Preventive Measures to Control Plant Viral Diseases:

• Use disease-resistant plant varieties
• Use certified virus-free seeds or planting materials
• Adopt crop rotation of host crops with non-host crops to break the cycle of viral infections in the soil and reduce the risk of virus buildup
• Cultivate trap crops to avoid disease-causing insect vectors ( marigold in bhendi and cowpea in cucurbits)
• Practice proper sanitation practices by removing and destroying infected plants, debris and disinfect equipments to prevent the spread of viral diseases
• Isolate the plants that are known to be infected
• Control the disease-causing insect vectors

Management of White fly, Aphids, Thrips, Leafhoppers:

Product name	Technical name	Dosage	Crops
Mechanical Management
Barrix Magic Sticker Chromatic Trap Yellow Sheet	Chromatic trap	10 sheets/acre	All crops
Biological Management
Econeem Plus	Azadiractin 10000 PPM	2.5 ml/lit water	Cotton, Chilli, Soyabean, Fruit Crops, Bulb Crops, Root Crops, Leafy Vegetables, Cereals, Field Crops
Amruth Alestra Bio Insecticide	Verticillium lecanii	2 ml/lit water	Papaya, Guava, Chilli, Cotton, Cereals, Pulses, Sugarcane, Fruits, Vegetables
Viro Raze Bio Viricide	Plant extracts	2 ml/lit water	Vegetables, Fruits, Pulses, Cereals
Geolife No Virus	Plant extracts	5 ml/ lit water	Vegetables, Fruits & Pulses
Chemical Management
Benevia Insecticide	Cyantraniliprole 10.26% OD	2.0 ml/lit water	Chilli, Melons, Tomato, Cotton
Actara Insecticide	Thiamethoxam 25 % WG	0.5 gm/lit water	Vegetables, Rice, Cotton
Katyayani Acepro Insecticide	Acetamiprid 20% SP	0.5 gm/lit water	Cotton, Rice, Chilli, Okra
Confidor Insecticide	Imidacloprid 17.8% SL	0.75 ml/lit water	Cotton, Rice, Chilli, Sugarcane, Tomato, Okra, Groundnut
Alika Insecticide	Thiamethoxam 12.6% + Lambda-cyhalothrin 9.5% ZC	0.5 ml/lit water	Rice, Potato, Brinjal, Maize
Polytrin C 44 EC Insecticide	Profenofos 40% + Cypermethrin 4% EC	2 ml/lit water	Tomato, Cucurbits and Cotton
Police Insecticide	Fipronil 40% + Imidacloprid 40% WG	0.2 gm/lit water	Cotton, Paddy, Vegetables, Sugarcane, Groundnut, Citrus
Pegasus Insecticide	Diafenthiuron 50% WP	1 gm/lit water	Cabbage, Kale, Broccoli, Cauliflower, French beans, Black beans
Starthene Insecticide	Acephate 75 % SP	2.5 gm/lit water	Cotton, Paddy, Vegetables

Management of Mites:

Product name	Technical name	Dosage
Biological Management
Amruth Almite Bio Insecticide	Paecilomycis fumosoroseus	2 ml per lit water
Perfomite Insecticide	Phyto-extracts - 30%, Enzyme extracts - 5%, Chitin Dissolvers	2 ml/lit water
Chemical Management
Intrepid Insecticide	Chlorfenapyr 10% SC	1.5 ml/lit water
Oberon Insecticide	Spiromesifen 22.9% SC	0.3 ml/lit water
Maiden Insecticide	Hexythiazox 5.45% EC	1 ml/lit water

Conclusion:

Plant viral diseases significantly affect crop production in India. These viruses can spread through insects or mechanical means, leading to significant yield loss. Effective management strategies can help prevent the spread of plant viruses and reduce their impact on crops. Using virus-free planting materials, practising good sanitation, controlling vectors with insecticides and implementing crop rotation can help prevent the spread of viruses.

Frequently Asked Questions

What are the common plant virus symptoms?

Stunted growth, yellowing, mosaic patterns, leaf distortion, and reduced yield.

Which crops are most affected by viral diseases in India?

Crops like tomato, chilli, paddy, banana, and cucurbits are commonly affected.

What are the best methods for plant disease management of viruses?

Use resistant varieties, virus-free seeds, control insects, and maintain field hygiene.