INTRODUCTION TO PLANT VIRUSES

1. INTRODUCTION TO PLANT VIRUSES
Virus:
Virus is set of one or more nucleic acid template molecules normally
encased in coats of protein or lip-protein and organize its own
replication only within specific host cells
Virion:
A complete mature viral particle is called virion
Prion:
Smaller infectious protein particles encoded by a chromosomal gene
of the host cells
Viroids: Small, low-molecular-weight ribonucleic acids (RNAs) that
can infect plant cells, replicate themselves and cause disease. OR
Naked, single-stranded circular molecule of infectious RNA called
viroid
Virusoids:
The extra-small circular RNA component of some isometric RNA
viruses

2. Importance of Plant Viruses
➢ Plant viruses are viruses that multiply by using
the material synthesized by the host to
manufacture new virus particles and cause
infection
➢ Beneficial Aspects:
➢ Used as color breaking agent in ornamental
plants. Ornamental plants become attractive e.g.
Tulip mosaic virus
➢ Used as a vector in genetic engineering, CuMV
➢ Viruses used as a cross protection

3. Harmful Aspects
➢ Causes harmful diseases in humans, animals,
and plants
➢ Cause reduction in the growth of the plants.
➢ Reduction in yield and ultimately failure of the
crop
➢ Affect the quality and quantity of the production
➢ Make the plants more vulnerable to other
organisms (Insects) e.g. TMV, SCMV, CLCuV,
CTV

4. COTTON LEAF CURL DISEASE
CLCuV, ssDNA
Genus: Begomovirus, Family: Geminiviridae
➢ Occurrence & Importance:
➢ First reported in Nigeria in 1912
➢ In 1959 from Philippines
➢ In 1967 in Pakistan near Multan
➢ Epidemic form in 1993-95 in Pakistan
➢ Most serious disease of cotton
➢ Cause losses from 22.38-68.50%

5. Symptoms
➢ Thickening of veins
➢ Color of infected plants become dark
green
➢ Upward or downward curling of leaves
➢ Leaf enation
➢ Twisted leaf petioles
➢ Stunting of plants

6. Symptoms

7. Symptoms

10. Disease Cycle
➢ Not seed or soil-borne
➢ Over winter on alternate hosts (tomato,
tobacco, beans, lehli, okra, datura etc
➢ Transmitted by whitefly (Bemisia tabaci)
➢ 30 Min. feeding on infected plants
➢ 24 hours latent period
➢ 30 Min. inoculation feeding period
➢ Retention period: through out life of
whitefly

12. Epidemiology
➢ Minimum temp. 27-28 0C
➢ Maximum temp. 38-40 0C
➢ Relative humidity: 56-60%
➢ Susceptible host on large area
➢ Less rainfall or no rainfall
➢ Abundance of whitefly population

13. Management
➢ Tolerant varieties like Allah Din One (A-
One), MNH-886 and FH-142
➢ Destruction of alternate hosts
➢ Uproot & burry first observed infected
plants
➢ Control insect vector (Imidacloprid, polo)
➢ Use of nutrients also help to reduce the
disease incidence

14. BANANA BUNCHY TOP DISEASE
(BBTV), ssDNA VIRUS
(Genus Babuvirus, Family Nanoviridae)
➢ Most important disease of banana crop
➢ Occur in all banana producing countries
(Fiji, Indonesia, Malaysia, Australia, Sri-
lanka, Pakistan, India)
➢ Infected plants produce no fruits

15. Symptoms
➢ Dark green streaks seen on petioles &
veins of new leaves looking against light
➢ Leaves arise in clusters
➢ Margins of leaves become chlorotic &
rolled upward
➢ Top of plant become narrow, upright &
closer appearing bunchy
➢ Plants show stunted growth
➢ Inflorescence fails to emerge

17. Disease cycle
➢ Vector: Black banana aphid (Pentalonia
nigronervosa)
➢ Also transmitted through propagative
materials (rhizomes, suckers, tissue-
cultured meristem)
➢ Aphid feed 17 hrs to become infective
➢ Maxi. Vector concentration at base of stem

18. Disease cycle

19. Epidemiology
➢ 18-20 0C temperature
➢ 41-84% Relative Humidity

20. Management
➢ Quarantine measures
➢ Use of virus free propagative material
➢ Locating new plantation away from old
➢ Destroying all volunteer banana plants
➢ Uprooting & burning of infected plants
➢ Control vector with insecticidal soap water spray
or insecticides (Prentox Diazinon AG500)
➢ Cultivate resistant varieties (Gross Michel)

21. Potato Leaf Roll Disease
(PLRV), ssRNA
Genus: Polerovirus, Family: Luteoviridae
➢ Occur world wide
➢ Most destructive virus of potato
➢ Yield losses more than 50%

22. Symptoms
➢ Appear mostly on lower leaves
➢ Leaflets roll upwards
➢ Margins & tips of leaves become yellow
➢ Leaves become leathery & brittle
➢ Plants stunted & have upright growth
➢ No. of tubers/plant & size is reduced
➢ Phloem necrosis occur in tubers

25. Disease cycle
➢ More than 10 species of aphid act as
vector (Myzus persicae)
➢ Infected tubers are primary source of
infection
➢ Aphid feed for several hrs (48-54 hrs)
➢ Alternate hosts are Datura stramonium

26. Epidemiology
➢ 15-20 0C temperature
➢ 40-65% Relative Humidity

27. Management
➢ Obtain certified seed
➢ Plant early in the season
➢ Pulled out sick plants as soon as located
➢ Detop plants in last week of December
➢ Apply systemic insecticides (aldicarb,
carbofuran)

28. Tobacco Mosaic Virus
(TMV) ss-RNA
Genus: Tobamovirus, Family: Virgaviridae
➢ First virus ever discovered in history
➢ Known to occur in all the tobacco growing
countries of the world
➢ 55% reduction in yield has been reported
➢ Sub stranded produce fetch low price in
the market

29. Symptoms
➢ Leaves show mild veins clearing
➢ Mottle and mosaic pattern
➢ Light discoloration along the veins of
young leaves
➢ Wrinkling, crinkling, twisting margins and
narrowing of leaf lets
➢ Dwarfing of entire plant

31. Disease cycle and epidemiology
➢ Survive in herbaceous and woody plants
➢ Tomato, Potato, pepper grown indoor are source
of infection
➢ Virus present in plant debris, soil, cloths and
even manufactured tobacco cigarette and cigar
➢ Contact with the wounded plants
➢ No insect vector, Mechanical transmission
➢ Wide host range of 500 species of flowering
plants
➢ Temp. 28-32 ºC, RH 44-56%

32. Management
➢ Use clean and healthy seed in the nursery
➢ All workers should disinfect their hands
➢ Avoid chewing of tobacco in the field
➢ Rouging out infected plants
➢ Crop rotation with maize and wheat, avoiding
tomato and pepper
➢ Healthy leaves harvest first than infected one
➢ Field sanitation practices

33. Sugarcane Mosaic Virus Disease
(SCMV) ss-RNA
Family: Potyviridae Genus: Potyvirus
➢ First recorded in Java in 1892, in Punjab in
1926-27
➢ Occur in every sugarcane growing
country
➢ Estimated yield losses vary greatly upon
cultivar and environmental conditions

34. SYMPTOMS
➢ Contrasting shades of green, islands of normal
green or yellowish chlorotic areas on the leaf
blade
➢ leaf reddening or necrosis
➢ Chlorotic areas most evident at base of the leaf
➢ Chlorotic areas may also be present on the leaf
sheath, but rarely on the stalk
➢ Young, rapidly growing plants are more
susceptible to infection

36. Disease cycle and epidemiology
➢ There are three principal modes of spread
of SCMV:
➢ (1) by aphid vectors,
➢ (2) by infected seed cane and
➢ (3) by mechanical inoculation.
➢ Only aphid vectors and infected seed cane
are important in the field.
➢ Temp. 35-38 ºC, RH 68-78%

37. Management
➢ Resistant varieties (CPF 242, HSF 240, SPF
234) is the most effective method to control
➢ Use disease free seed canes
➢ Management practices targeting insect vectors
➢ Control of mosaic through heat treatment only
practical in quarantine situations
➢ Some plants recover from mosaic by nutritional
application

38. Citrus Tristeza Virus (CTV)
or Quick decline, ss-RNA
Family: Closteroviridae Genus: Closterovirus
➢ Biggest threats to citrus production in globe
➢ More than 30 virus, virus-like diseases of citrus
known in the world, of which CTV is the most
destructive.
➢ The first tristeza disaster was reported in 1930's
in Argentina, where 90% of the citrus was
planted on sour orange rootstock

39. Symptoms
➢ Yellowing of leaves
➢ Dieback of the phloem in the sour orange
rootstock below the bud union
➢ Rootstock being girdled
➢ 'Slow decline' where trees decline in a period of
years
➢ Stunting where the virus does not kill the tree,
but the tree does not grow
➢ Deep pits are present under depressed areas of
the bark

41. Disease cycle
➢ Vectors of CTV are black or brown citrus aphid
(Toxoptera citricida)
➢ Due to the aphid introduction, CTV rate of
spread has increased dramatically
➢ Additionally, growers have aided in the spread of
the virus with the propagation of trees using
infected bud-wood.
➢ Temperature, 20-27 0C RH, 55-70%

42. Management
➢ Exclude any introduction of severe strains
➢ Need for mild strain protection in the future
➢ Strict control by quarantine must be continued
➢ Rootstocks that offer resistance to tristeza
decline include the citranges (C-35, Carrizo,
Troyer), Citrumelos (Swingle), mandarins

43. THANKS
Dr. Safdar Ali
Dr. Luqman Amrao