Viral Plant Diseases

• Viruses are more differ greatly from other plant pathogens like fungi and bacteria as because of their simplicity in chemical nature and special type of parasitism.

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• It is much more difficult to control viruses.

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• Viral diseases of plants exhibit a variety of symptoms

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• Plants sometimes infected by more than one kind of virus at the same time.

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• Plant viral diseases may damage any or all parts of a plant and may cause economic losses by reducing yields and quality of plant products.

Symptoms of Virus Plants Diseases

• White or yellow colour spots appear on leaf surface

Mosaic

• Clearing or chlorosis of the tissue in or immediately adjacent to the veins.

Vein clearing and vein banding

• Various spots appears and consists of different types of chlorosis and necrosis.

Ring spots

• To kill cells, tissues or the whole plant.

Necrosis

Wilt

• The outer whorls of leaves droop and become yellow
• Involving a reduction in the size of the leaves,

flowers and fruits.

Stunning

• Uneven growth of leaf lamina. Leaves become curled, brittle and shows puckering

Changes in leaf form

• Viral infections as mottling on Cucumber and papaya a due to mosaic type of viruses

Fruit abnormalities

Transmission of Viruses

Seed Transmission

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Transmission by Grafting

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Transmission by Vegetative Propagation

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Transmission by Parasitic Phanerogams

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Transmission by Insects

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Transmission by Fungi

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Transmission

through weeds

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Soil Transmission

©Agrios, 2005, 5^th Edition

Control Measures

• Seeds selection from disease- free localities.
• Select the planting material from plants that are not infected.
• Tuber indexing: Select virus-free potato tubers for multiplication on a large scale.
• Roguing: Regular removal of all diseased plants is very effective.
• Destruction of weed hosts
• Eradication of diseased plants to eliminate inoculum
• Resistant varieties
• Temperature treatments
• Systems of quarantine, inspection, and certification

Viral Disease- Tobacco Mosaic Virus

• Tobacco mosaic virus causes a mottled browning of tobacco leaves which causes major economic losses.

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• Adolf Mayer first described the tobacco mosaic disease that could be transferred between plants.

• TMV is very prevalent in many ornamentals in greenhouses and botanical gardens as a result of transmission from tobacco products.

©Morningchores.com

• The pathogen is tobacco mosaic virus has a rod-like appearance

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• The virus particle measures 18 by 300

nanometers

• Their genome consists of one single-stranded RNA and protein coat consists of a single species of protein subunit arranged in a helix.

• The virus is transmitted easily by handling contaminated tobacco products or implements, or infected tobacco plants, and then healthy susceptible plants.

©brainkart.com

Symptoms of TMV

• Growth of the infected plant can be stunted.

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• Various degrees of mottling and chlorosis occurs in

leaves.

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• Leaf curling, distortion, and dwarfing of leaves observed in diseased plants.

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• Common signs include mosaic-like patches

(mottling) on the leaves, curling of leaves.

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• Lower leaves shows mosaic burn during hot and dry

weather.

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• Reduction in yield and quality of products

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• Diseased plant shows yellowing of plant tissues.

Control Measures

• Remove all crop debris from the land.

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• Disinfect the tools and equipments in solution for at least 10

minutes and rinse with tap water.

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• Use Resistant varieties.

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• Sanitation includes removing infected plants and then washing hands with soap

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• Avoid planting of susceptible hosts for two years in fields or

seedbeds where a diseased crop was grown.

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• Regular rouging of diseased plants

Disease Cycle of TMV

Source: Plant Pathology, Mehrotra

Viral Disease-Bunchy Top of Banana

• Bunchy top of Banana is the most serious disease in banana .
• It is widely distributed along banana growing

countries.

• It is a viral disease caused by the virus Banana virus – I,
• It produces a cluster of leaves at the apex forming a rosette in the diseased plant.
• The Banana bunchy top disease was first reported from Fiji in 1879.
• In India, the disease was recorded for the first

time in 1940 from Kerala State

Source: Plant pathology, Vardhman Mahaveer Open University, Kota, 2017.

• This disease is caused by a virus namely Bunchy top virus – I or

Banana Virus – I or Musa virus-I.

• The genome of BBTV is made up of at least six circular, single- stranded DNA components, each about 1 kilo-base pair in length.
• The virus is being transmitted by a aphid vector Pentalonia

nigronervosa

• In the infected plant, the virus is present in all the parts including the rhizomes and the suckers.
• The aphid acquires the virus in a feeding period of 24 hours and

transmits the virus to the healthy plants.

• The aphid (vector) remains virulferous for about 13 days after the acquisition of virus.
• The aphid usually attacks the host plant around the basal portion of

the Pseudostem.

• The insect may carry the disease to long distances.

Symptoms

• The disease may occur and show the symptoms of bunchy top at any stage of plant growth.
• In infected plant leaves are bunched together at the top of the pseudostem to form a rosette appearance.
• The appearance of irregular, brown streaks along the secondary veins are the first external symptom.
• The midrib portion on the undersurface of the leaf

shows chlorotic streaks.

• Appearance of brown streaks On leaf petiole.
• The leaf size becomes smaller and narrow.
• In the diseased plant, leaves are clustered at the

apex forming a rosette.

• The infected plant shows stunted growth. Usually the infected plants do not bear any fruits.
• The phloem of the infected plant is disorganized to some extent

Source: Plant pathology, Vardhman Mahaveer Open University, Kota, 2017.

Control Measures

• The diseased plants should be thoroughly and carefully dug out with suckers and destroyed by burning.
• Exclusion of diseased suckers and plants has been recommended.
• The infected plants along with the aphids should be killed by pouring 50ml of kerosene on each plant.
• The virus particles can be killed by injecting the herbicides agrokone (or) 2,4-D (2,4-dichlorophenoxy acetic acid) or MCPA (2-Methyl-1-4 chlorophenoxy acetic acid) in the diseased plant.
• Disease free suxkers or certified virus free suckers should be used for planting.
• Strict control on the entry of banana plants from other states and

must be checked for

movement of suckers within the state

infection.

• No resistant varieties have been evolved.

Source: Plant pathology, Vardhman Mahaveer Open University, Kota, 2017.

Disease Cycle of Bunchy Top of Banana

Bunchy Top

of Banana

Aphids feed on the infected plant phloem tissues

Then the aphid injects saliva and sucks the cell contents

Dispersal infected plant to healthy plant

Injection of viral inoculum to healthy plant

it takes a month for the symptoms to appear after infection

Symptoms

on Plant

Source: BohatALA By picesgirl