This document provides information on several plant viruses. It defines viruses and describes their structure. It then discusses the history of the earliest documented plant virus. The document proceeds to provide details on several specific plant viruses, including Tobacco mosaic virus, Potato virus Y, Sugarcane mosaic virus, Citrus tristeza virus, and Cotton leaf curl virus. For each virus, it outlines key facts like genome, geographic occurrence, symptoms caused, transmission method, environmental conditions needed, and control methods.

1. Course No. PP-202 Module No. 2

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”.

3. Rod-shaped Flexuous thread
Isometric virus Bacilliform

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

8. Wrinkling
crinkling twisting
margins and
narrowing of leaf
lets
Dwarfing of
entire plant
Mark reduction
in yield

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

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

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

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