2. Viruses can be defined as “small
obligate intracellular parasites, which
contain either an RNA or DNA genome
surrounded by a protective, virus-
coded protein coat”.
4. In 1886, Dutchman Adolph Mayer injected juice
obtained from tobacco plant leaves showing various
patterns of greenish yellow mosaic into healthy
tobacco plants and the latter then developed similar
mosaic patterns.
History
5. Earliest Record of Plant Virus
Yellow Vein Net Disease of Eupatorium was
described in a Japanese poem, written in the
eighth century (Saunders et al., 2003)
6. ssRNA
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
7. Leaves show mild
veins clearing
Mottle and mosaic
pattern
Light discoloration
along the veins of
young leaves
9. 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%
10. Use clean and healthy seed in the nursery
All workers should disinfect their hands
Rouging
Crop rotation maize and wheat, avoiding
tomato and pepper
Healthy leaves harvest first than infected one
Field sanitation practices
11. ssRNA
Occur world wide
Most destructive virus of potato
12. Leaf mottling or yellowing, leaf
deformation, necrotic leaf spots or
rings, veinal necrosis,
Necrotic stem-streaking, leaf drop and
premature death of stems.
The tubers remain smaller in size
Mild strains and tolerant cultivars may
develop milder foliage symptoms without any
necrosis, leaf drop or premature death of
shoots.
Secondary symptoms includes dwarfing and
wrinkling of leaves
13.
14. More than 10 species of aphids act as vector
(Myzus persicae)
Infected tubers are primary source infection
Aphid feed for several hrs (48-54 hrs)
Alternate hosts are datura stramonium,
physalis floridana
15. 15-20 0c temperature
40-65% Relative Humidity
16. ssRNA
First recorded in Java in 1892, in Punjab in
1926-27
Occur in every sugarcane growing country.
Estimated yield losses vary greatly
depending on the time period and
sugarcane growing area involved.
17. Contrasting shades of green, islands of
normal green or yellowish chlorotic areas on
the leaf blade
Infection accompanied by varying degrees of
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
18.
19. 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%
20. At least 12 species of aphids transmit SCMV
The spread of mosaic is most rapid when
vector populations are high, susceptible
sugarcane varieties are grown, and SCMV-
infected plants are plentiful.
Mosaic is primarily spread by planting
infected seed cane.
21. Resistant varieties is the most effective
method of mosaic control.
Periodic surveys of SCMV strains are
necessary to tested against prevalent
strains.
Management practices targeting insect
vectors and control methods aimed at
eradication have not been very effective.
22. ssRNA
Biggest threats to citrus production in
globe.
More than 30 virus, virus-like diseases of
citrus known in the world, of which CTV is
most destructive.
In 1981, the total world loss attributable to
this disease was estimated at 50 million
trees.
23. Quick decline
Dieback of the
phloem in the sour
orange rootstock
below the bud
union.
slow decline' where
trees decline in a
period of years.
24. A third common
symptom is
stunting where the
virus does not kill
the tree, but the
tree does not grow.
Sweet orange cv. Valencia grafted on
sour orange rootstock affected by Citrus
tristeza closterovirus (CTV).
25. Either deep pits are
present under
depressed areas of
the bark, or more
severe strains may
cause a more
general distribution
of the stem
pitting, with a
thickening of the
bark and many fine
pits.
Stem pitting induced by CTV
on a grapefruit trunk
26. Vein clearing induced
by CTV in
inoculated Mexican
lime (C. aurantiifolia)
seedlings
incubated in a
glasshouse at 18-25°C.
27. Vectors of CTV are black citrus aphid
(Toxoptera citricida), 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.
28. 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
29. ssDNA
First reported in Nigeria in 1912
In 1959 from Philippines
In 1967 in Pakistan near Multan
30. Thickening of veins
Color become dark green
Upward or downward curling of leaves
Leaf enation
Twisted leaf petioles
Stunted growth
31.
32. Not seed-borne 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
33. Minimum temp. 25-30 c
Maximum temp. 33-45 c
Optimum temp. 32 c
Relative humidity: 56-60%
34. Resistant varieties, NIBGE-2, NIAB-111, PB-
899, CIM-446, MNH-786
Destruction of alternate hosts
Control insect vector (Imidacloprid)
Uproot & burry first observed infected plants