PG AND RESEARCH DEPARTMENT OF MICROBIOLOGY - SRI PARAMAKALYANI COLLEGE - ALWARKURICHI

1. SRI PARAMAKALYANI COLLEGE
( REACCREDITEDWITH B GRADE WITH A CGPA OF 2.71 IN THE II CYCLEBY NAAC
AFFILIATED TO MANONMANIAMSUNDARANAR UNIVERSITY, TIRUNELVELI)
ALWARKURICHI627 412
POST GRADUATE & RESEARCHCENTRE – DEPARTMENT OF MICROBIOLOGY
(GOVERNMENT AIDED)
II SEM – CORE – VIROLOGY
UNIT III – COMMON VIRAL DISEASES OF CROP PLANT
SUBMITTED TO SUBMITTED BY,
DR. C. MARIAPPAN , PH.D, S. SARAL BEEVI,
ASSISTANT PROFESSOR, REG NO: 20211232516123,
SRI PARAMAKALYANI COLLEGE, SRI PARAMAKALYANI COLLEGE,
ALWARKURCHI. ALWARKURCHI.

2. OUTLINE
- Plant virus
- Common plant viral diseases
- Pathogen
- Symptoms
-Treatment
- Prevention
- Control

3. PLANT VIRUS
• Plant viruses are viruses that affect plants. Like all other viruses, plant
viruses are obligate intracellular parasites that do not have the molecular
machinery to replicate without a host. Plant viruses can be pathogenic to
higher plants.

4. COMMON PLANT VIRAL DISEASES IN PADDY
• Rice tungro disease : Rice tungro virus (RTSV, RTBV)
• Rice grassy stunt
• Rice ragged stunt
• Rice yellow mottling

5. RICE TUNGRO DISEASE : RICE TUNGRO VIRUS (RTSV, RTBV)
• Rice tungro disease is caused by the combination of two viruses, which are
transmitted by leafhoppers. It causes leaf discoloration, stunted growth,
reduced tiller numbers and sterile or partly filled grains. Tungro infects
cultivated rice, some wild rice relatives and other grassy weeds commonly
found in rice paddies.

6. PATHOGEN
• Two morphologically unrelated viruses present in phloem cells. Rice tungro
bacilliform virus (RTBV) bacilliform capsid, circular ds DNA genome and
Rice tungro spherical virus (RTSV) isometric capsid ss RNA genome.

7. SYMPTOMS
• Infection occurs both in the nursery and main field.
• Plants are markedly stunted.
• Leaves show yellow to orange discoloration and interveinal chlorosis.
• Young leaves are sometimes mottled while rusty spots appear on older
leaves. Tillering is reduced with poor root system.
• Panicles not formed in very early infection, if formed, remain with few,
deformed and chaffy grains.

8. TREATMENT
• Light traps are to be set up to attract and control the leaf hopper vectors
as well as to monitor the population.
• In the early morning, the population of leafhopper alighting near the light
trap should be killed by spraying/dusting the insecticides. This should be
practiced every day.

9. • Spray Two rounds of any one of the following insecticides
• Thiamethoxam 25 WDG 100g/ha
• Imidacloprid 17.8 SL 100ml/ha
• at 15 and 30 days after transplanting. The vegetation on the bunds should
also be sprayed with the insecticides.

10. PREVENTIVE MEASURES
• Plant more resistant varieties if available.
• Plant early to avoid peaks populations of this insect.
• Remove weeds in and around the field.
• Control insecticides in order not to affect beneficial insects.
• Plow under infected plant residues or better burn them.
• Alternatively, destroy infected plants after harvest.

11. CONTROL
• Organic Control
• Light traps have successfully been used to attract and control the green
leafhopper vectors as well as to monitor the population. In the early
morning, the population of leafhopper alighting near the light trap should
be caught and disposed of, alternatively killed by spraying/dusting
insecticides. This should be practiced every day.
• Destroy infected plants and plow under infected plant residues or better
burn them.

12. • Chemical control
• Always consider an integrated approach with preventive measures together
with biological treatments if available. Spraying insecticides based on
buprofezin or pymetrozine at 15 and 30 days after transplanting can work
if done in a timely manner. However, the insects can move to surrounding
fields and spread tungro rapidly in very short times. Therefore, the
vegetation around the field should also be sprayed with the insecticides.

13. • Avoid products based on chlorpyriphos, lamda cyhalothrin or other
synthetic pyrethroid combinations, to which the leafhoppers have become
partly resistant.
• Spraying insecticides can suppress the populations of the green
leafhoppers which means it will reduce the speed of spreading the virus.
Some known insecticides can be used to control green leafhoppers.

14. RICE YELLOW MOTTLE DISEASE
• Rice yellow mottle virus is a plant pathogenic virus, belonging to the genus
Sobemovirus. The genome is a positive-sense single strand RNA of 4450
nucleotides in length and is not polyadenylated.
• Mottling usually consists of yellowish spots on plants, and is usually a sign of
disease or malnutrition.

15. PATHOGEN
• Rice yellow mottle virus (RYMV) caused by Solemoviridae is a major biotic
factor affecting rice production and continues to be an important pathogen
in SSA. To date, six pathogenic strains have been reported. RYMV infects
rice plants through wounds and rice feeding vectors.

16. SYMPTOMS
• Younger leaves are mottled with yellow to green spots.
• After infection (2 weeks) these spots elongate parallel
to the leaf veins.
• In the center of the yellow streaks, dark patches develop.
• Older leaves show yellow or orange discoloration. The
growth of the plants can be stunted and the yield is reduced.

17. TREATMENT
• Employ the use of large-scale synchronous planting combined with fallow
period to prevent the buildup of the virus and vector.
• plow under-infected crop residues, volunteer rice, infected ratoons,
alternate hosts of the virus, and the vector immediately after harvest to
reduce the primary inoculum in the field and prevent continuous survival of
the virus and the vector.

18. • Establish the crop before the increase in the vector population.
• Roguing and burning infected plants, especially when infection is still low.
• Regular weeding during the cropping season and even after harvest to
reduce sources of primary inoculum.

19. PREVENTIVE MEASURES
• Resistant and tolerant varieties are available.
• Using nursery sites which haven’t been infected previously or direct sowing
in the field can also help prevent the spread of the virus.
• Planting the crop as early as possible can avoid the peak period of insect
vectors of the virus. In addition, synchronising the planting in different fields
can prevent the virus from spreading to younger crops.

20. • Maintaining weeds to control other hosts of the virus and clearing bushes
around fields to control breeding sites for insect vectors can also prevent
RYMV spread.
• Sanitation procedures can reduce the spread of RYMV. CABI recommends
cleaning weeds from irrigation canals and around rice fields, especially
during the off season, to remove the virus and its insect vectors will remove
the virus and insect vectors.

21. • Cleaning of farm machinery can reduce spread prevent mechanical
spread. This also applies to cleaning any farm machinery after each use.

22. CONTROL
• RYMV will completely kill susceptible varieties; if detected, removing
infected plants and destroying them can prevent further spread. It has also
been reduce the application of fertiliser on infected plants.
• There are no chemical control methods to directly stop the spread of RYMV.
However, there are available insecticides to control vectors of the virus in
some countries; suitable chemicals vary depending on country specific
guidelines.

23. COMMON PLANT VIRAL DISEASES IN COTTON
• Leaf crumple
• Leaf curl
• Leaf mottle
• Leaf role

24. LEAF MOTTLE DISEASE
• A zinc deficiency disease is characterized by a partial chlorosis, reduced
size of leaves and fruits, and stunting
• A virus disease is characterized by chlorotic mottling, puckering, distortion,
and wrinkling of the leaves

25. PATHOGEN
• The leaf mottle viral disease was transmitted by grafting to other XL.l
plants and to X1730 A and Domains Sakel, identical symptoms appearing
on all 3.

26. SYMPTOMS
• The primary symptom of cotton leaf mottle virus is the
upward curling of leaves.
• Additionally, leaf veins can thicken and darken, and
outgrowths (enactions) may form on the undersides of
leaves, typically in the shape of leaves.
• Flowers may stay closed and then drop along with the bolls.
If plants are infected early in the season, their growth will be
stunted and yield will be reduced significantly.

27. TREATMENT
• Although there are virtually no antiviral compounds available to cure plants
with viral diseases.
• Efficient control measures can greatly mitigate or prevent disease from
occurring.
• Virus identification is a mandatory first step in the management of a
disease caused by a virus.

28. PREVENTIVE MEASURES
• Use certified disease-free seeds and ensure transplants are healthy.
• Control whitefly populations and protect seedlings in particular from them.
• Ensure a weed-free field and surroundings.
• Practice crop rotation by not planting cotton near alternative hosts.
• Plow under or burn all plant debris after harvest.

29. CONTROL
• Organic Control
• Whitefly populations can generally be controlled by natural enemies (e.g.
lacewings, bigeyed bugs, minute pirate bugs), so be careful not to kill them
with rampant spraying of chemical pesticides.
• Neem oil or petroleum-based oils can be used and should thoroughly cover
the plants, particularly the undersides of leaves.

30. • Recent research has also indicated the potential of using biocontrol agents
such as beneficial isolated bacterial strains (Bacillus, Pseudomonas and
Burkholderia) as a means of reducing the incidence of the virus.
• Chemical Control
• Always consider an integrated approach with preventive measures together
with biological treatments if available.

31. • There are no known methods for preventing or reducing cotton leaf curl
virus. Chemical control in the form of insecticides can be used to control the
whitefly population, such as imadacloprid or dinotefuran.
• Insecticides should be approached with caution however, because excessive
usage of insecticides has caused many whitefly species to become resistant
to them. To reduce the likelihood of this occurring, be sure to rotate between
insecticides.

32. COMMON PLANT VIRAL DISEASES IN TOMATO
• Tobacco mosaic virus (TMV)
• Tomato mosaic virus (ToMV)
• Tomato spotted wilt virus (TSWV)
• Pepino mosaic virus (PepMV)
• Cucumber mosaic virus (CMV)

33. TOMATO MOSAIC VIRAL DISEASE
• It is a kind of plant virus with worldwide distribution and has a wide range
of hosts, which can not only infect Solanaceae, Cruciferae, and other
vegetable crops, but also infect flowers and seedlings, etc.

34. PATHOGEN
• ToMV is a positive-sense, single-stranded RNA virus belonging to the
Virgaviridae family, Tobamovirus genus.

35. SYMPTOMS
• It Seen as a general mottling or mosaic appearance on foliage.
• Light and darker green mosaic leaf mottle, sometimes with distortion
of younger leaves; this is the most common reaction in summer in
glasshouses.
• In winter, with low light intensity, short days and temperatures not
above 20°C, plants are often severely stunted and leaves distorted
to ‘fern-leaf’ or tendril shape, but mottling may be slight.

36. • Plants are less vigorous, and fruit yield is reduced by 3 to 23%. Tomato
mosaic virus strains occur in Chenopodium murale , causing severe stunting,
distortion and necrosis , and in pear associated with a diffuse chlorotic leaf
spotting.

37. TREATMENT
• Remove diseased plants from the field as soon as virus symptoms are
noticed. This will reduce the spread of the virus by direct contact between
plants.
• Work in diseased areas last after working in unaffected parts of a field.
Wash clothing that comes into contact with ToMV-infected plants with hot
water and a detergent.

38. • Disinfect tools, stakes, and equipment before moving from diseased areas
to healthy areas. This can be done by:
• (1) heating or steaming at 150°C for 30 minutes.
• (2) soaking 10 minutes in 1% formaldehyde or 0.1% sodium hypochloride.

39. PREVENTIVE MEASURES
• Keep weeds controlled within and around the garden site, as these may be
alternate hosts for whiteflies.
• Reflective mulches (aluminum or silver-colored) can be used in the rows to
reduce whitefly feeding.
• Spot treat with least-toxic, natural pest control products, such as Safer
Soap, Bon-Neem, and diatomaceous earth, to reduce the number of
disease-carrying insects.

40. • Harvest-Guard row cover will help keep insect pests off vulnerable crops/
transplants and should be installed until bloom.
• Remove all perennial weeds, using least-toxic herbicides, within 100 yards
of your garden plot.
• The virus can be spread through human activity, tools, and equipment.
Frequently wash your hands and disinfect garden tools, stakes, ties, pots,
greenhouse benches, etc. (one part bleach to 4 parts water) to reduce the
risk of contamination.

41. • Avoid working in the garden during damp conditions (viruses are easily
spread when plants are wet).
• Avoid using tobacco around susceptible plants. Cigarettes and other
tobacco products may be infected and can spread the virus.
• Remove and destroy all infected plants (see Fall Garden Cleanup). Do not
compost

42. CONTROL
• Remove all infected plants and destroy them. Do not put them in the
compost pile, as the virus may persist in infected plant matter. Burn infected
plants or throw them out with the garbage.
• Monitor the rest of your plants closely, especially those that were located
near infected plants.
• Disinfect gardening tools after every use. Keep a bottle of a weak bleach
solution or other antiviral disinfectant to wipe your tools down with.

43. CUCUMBER MOSAIC VIRUS (CMV) DISEASE
• Cucumber mosaic virus (CMV) is one of the most common plant viruses,
causing yellow mottling, distorted leaves and stunted growth in a wide
range of garden plants, not just cucumbers.

44. PATHOGEN
• CMV is a linear positive-sense, single stranded RNA virus.
• It consist of three spherical particles each approximately 28 nm in
diameter. One particle containing RNA 1, another containing RNA 2, third
containing RNA 3.
• Each RNA molecule’ js enclosed within a protective protein coat.

45. SYMPTOMS
• Yellowish patches or green and yellow mottling on leave.
• Leaves curl downwards and are distorted and reduced in
size.
• Plants are stunted due to a shortening of the internodes
(lengths of stem between leaves.
• Reduction in yields and distorted fruit.
• In flowers white streaks known as ‘breaks’ appear.

46. TREATMENT
• Infected plants should be removed and destroyed to eliminate the plants as
potential reservoirs for the virus (which can subsequently be spread to other
nearby healthy plants).
• Infected plants can be burned (where allowed by local ordinance), deep
buried or hot composted.
• Killing infected plants with herbicides can also be an effective management
strategy.

47. PREVENTIVE MEASURES
• Use crop rotation.
• Eradicate weeds and volunteer tomato plants.
• Space plants to not touch, mulch plants, fertilize properly.
• Don’t wet tomato foliage with irrigation water, and keep the plants growing
vigorously.
• Trim off and dispose of infected lower branches and leaves.

48. CONTROL
• CULTURAL METHOD
• There is no perfect control for this virus.
• Removing weeds and diseased plants from fields can reduce the chance of
infection.
• Early planting of crops reduce aphids infestation.

49. • CHEMICAL METHOD
• Spray dimethoate:
• 2mlM/lit or Monocrotophos
• 1.5 mlM/lit to control insect vectors.
• Spray of mineral oil in plants to control aphids.

50. COMMON PLANT VIRAL DISEASES IN SUGARCANE
• Yellow leaf disease: Sugarcane yellow leaf virus (SCYLV) / Sugarcane
yellow leaf phytoplasma (SCYP)
• Sugarcane mosaic:Sugarcane mosaic virus (SCMV) / Sugarcane streak
mosaic virus (SCSMV)
• Leaf Fleck

51. SUGARCANE MOSAIC VIRUS
• Sugarcane mosaic virus (SCMV) is a plant pathogenic virus of the family
Potyviridae.
• As a viral infection, mosaic disease cannot be controlled by fungicides or
other pesticides. In some cases infection leads to severe damage. In the
worst cases, the disease may kill the entire lawn as the turfgrass declines.
This is referred to as lethal viral necrosis (LVN).MV

52. PATHOGEN
• Sugarcane mosaic virus (Marmor sacchari) is present in abundance in the
chlorotic lesions of the affected leaves.
• It belongs to the potato virus Y group.
• It causes varying degrees of destruction of the
chlorophyll, and hence the chlorotic symptom.

53. • The virus particles are rods, measuring in the range of 650-770x 12-15
pm.
• Several strains of the virus, designated as A,B,C,D,E,F and H and a few sub-
strains have been differentiated, based on their physical properties and
virulence.

54. SYMPTOMS
• SCMV causes systemic infection of the sugarcane plant: the whole plant,
including roots, contains virus.
• However, the symptoms (mosaic and/or necrosis) are observed on the
leaves and sometimes th.e stems.
• The disease appears more prominently on the basal portion of the
younger foliage as chlorotic or yellowish stripes alternate with normal
green portion of the leaf.

55. • As infection becomes severe, yellow stripes appear on the leaf sheath and stalks.
• Elongated necrotic lesions are produced on the stalks and stem
splitting occurs.
• The necrotic lesions also develop on the internodes and the
entire plant becomes stunted and chlorotic.
• Sometimes the whole plant is stunted and chlorotic, easily
dentified from a distance.

56. TREATMENT
• To minimize spread of sugarcane mosaic virus all equipment used should be
sanitized.
• Fungicides and other pesticides have been shown to be ineffective when
dealing with viral disease.
• The best way to deal with a viral disease is through plant host resistance.

57. PREVENTIVE MEASURES
• Disease free cane should be used as setts.
• Diseased plants should be dug as & burnt.
• Low lying areas avoided for cultivation.
• A 2-3 years rotation should be followed.
• Ratooning should be avoided.
• Use of resistant varieties, eg. Isward 254 Isward 1-16 Isward 1-17, etc.,

58. CONTROL
• Altering the times of planting and harvesting so that they do not coincide
with high aphid vector populations can reduce losses.
• Eradicate SCMV by roguing infected plants have rarely been successful.
• Saccharum spontaneum L. and S. barberi (Jesweit) carry resistance to mosaic
and so varieties with this background must be preferred.
• The spontaneum canes from java posses a high degree of resistance to
mosaic.

59. • The use of resistant varieties is the most effective method of mosaic control.
• Planting mosaic-free seed cane is essential.
• Rogue out the diseased clumps periodically. Select setts from the healthy
fields as the virus is sett-bome Aerated Steam Therapy (AST) at 56°C for 3
hrs, for setts before planting is advised.