Module 2nd,,, plant viruses


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Module 2nd,,, plant viruses

  1. 1. Course No. PP-202 Module No. 2
  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. 3. Rod-shaped Flexuous thread Isometric virus Bacilliform
  4. 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. 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. 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. 7.  Leaves show mild veins clearing  Mottle and mosaic pattern  Light discoloration along the veins of young leaves
  8. 8. Wrinkling crinkling twisting margins and narrowing of leaf lets Dwarfing of entire plant Mark reduction in yield
  9. 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. 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. 11.  ssRNA  Occur world wide  Most destructive virus of potato
  12. 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. 13.  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
  14. 14.  15-20 0c temperature  40-65% Relative Humidity
  15. 15.  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.
  16. 16.  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
  17. 17.  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%
  18. 18.  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.
  19. 19.  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.
  20. 20.  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.
  21. 21.  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.
  22. 22.  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).
  23. 23.  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
  24. 24. Vein clearing induced by CTV in inoculated Mexican lime (C. aurantiifolia) seedlings incubated in a glasshouse at 18-25°C.
  25. 25.  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.
  26. 26.  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
  27. 27. ssDNA First reported in Nigeria in 1912 In 1959 from Philippines In 1967 in Pakistan near Multan
  28. 28.  Thickening of veins  Color become dark green  Upward or downward curling of leaves  Leaf enation  Twisted leaf petioles  Stunted growth
  29. 29.  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
  30. 30.  Minimum temp. 25-30 c  Maximum temp. 33-45 c  Optimum temp. 32 c  Relative humidity: 56-60%
  31. 31.  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