Module 2nd,,, plant viruses
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Transcript of Module 2nd,,, plant viruses
Viral Disease
Course No. PP-202 Module No. 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”.
Rod-shaped Flexuous thread
Isometric virus Bacilliform
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
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)
Tobacco Mosaic Virus (TMV) 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
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
Mark reduction in yield
Epidemiology and Disease cycle
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%
Management 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
Potato leaf roll diseasePLRV
ssRNA Occur world wide Most destructive virus of potato
Symptoms 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
Disease cycle 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
Epidemiology 15-20 0c temperature 40-65% Relative Humidity
Sugarcane Mosaic Virus DiseaseSCMV 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.
SYMPTOMS
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
SPREAD 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%
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.
Management 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.
Citrus Tristeza Virus (CTV)
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.
Symptoms 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.
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).
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
Vein clearing induced by CTV ininoculated Mexican lime (C. aurantiifolia) seedlings incubated in a glasshouse at 18-25°C.
Disease cycle 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.
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
COTTON LEAF CURL DISEASE(CLCuV)
ssDNA
First reported in Nigeria in 1912
In 1959 from Philippines
In 1967 in Pakistan near Multan
Symptoms
Thickening of veins Color become dark green Upward or downward curling of leaves Leaf enation Twisted leaf petioles Stunted growth
Disease Cycle 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
Epidemiology Minimum temp. 25-30 c Maximum temp. 33-45 c Optimum temp. 32 c Relative humidity: 56-60%
Management 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