Symptoms of plant viruses

This slides contains basic information about symptoms caused by viruses on plants.

1. Welcome

2. Symptoms caused by plant viruses

3. Introduction Symptoms are host expressions or reflection of host response to diseased conditions. Symptoms are vary important to know that the plant normal function is disrupted. Viruses produce a wide range of symptoms. Viriods , phytoplasmas and some nutrient imbalances cause similar symptoms like viruses. that is why it is important to study about symptoms coursed by viruses for proper diagnosis of disease.

4. Symptoms caused by viruses can be divided into two broad categories. External / morphological symptoms. Internal / histological symptoms.

5. External symptoms External symptoms give the first clue about possible disease condition. External symptoms produced by viruses can be broadly categorized as. Colour deviation Necrosis in leaves and fruit Abnormalities in leaf shape and size Excessive growth (hyperplasia) Stem pitting, bark scalding and cracking

6. Colour deviation in leaves Mosaic = irregular patches of colors, dark green light green yellow etc appear on leaves.(tobacco mosaic virus). Mottling : evenly distributed alternate light and dark green patterns on leaves. (broad bean mottle). Variations : intermingled patches of chlorotic , green or other colour on leaves (carrot red leaf virus). Vein banding : region near the leaf vain remains darker than other tissues (TMV).

7. mosaic mottel discoloration Vein banding

8. Vein fleckring :water soaked areas on back of leaf corresponding to veins. (Citrus tristeza virus). Vein clearing : disappearance of green colour adjacent to veins of young leaves. Yellow vain : vain and veinlets turn yellow forming net like pattern (yellow vain mosaic of okra). Yellowing :entire leaf lamina turns golden yellow. (yellow mosaic of mung bean).

9. Vein fleckering Vein clearing Yellow vein yellowing

10. Vein blackening : veins and veinlets turn black (tobacco Necrosis) Chlorotic and necrotic local lesions: small chlorotic or necrotic lesions produce on leaf upon mechanical inoculation. Ring spot : Local lesion with central group of dead cells surrounded by one or more superficial concentric rings of dead cells with normal green tissue between them. (papaya ring spot)

11. Vein blackening Chlorotic and necrotic lesions ringspots

12. Colour deviation on stem Dark green patches on stem and out growth (sweet potato enation mosaic) Black streaks on stem (tobacco Necrosis)

13. Colour deviation in flower Colour braking : discontinuous streaks of light and dark colour are found in flower petals. ( canna mottle virus). Virescence : flowers turn green and leafy. (cotton virescence ).

14. tulipomania

15. Colour deviation fruit and seed Dark green colour patch on cucumber (CMV) water soaked rings appear on fruits (papaya ring spot virus). Specks and mottle on soybean seed due to soybean mosaic virus. Mottling of wheat seeds due to wheat streak mosaic virus.

16. Ringspots on fruits

17. Abnormalities in leaf shape Shoe string: leafleting in between vans is poorly developed or not developed (papaya ring spot). Enation and tuners : virus infection produces out growth associated with veins of leaves called enation . (pea enation mosaic) Blister : epidermis of leaf produces bubble like out growth (CMV).

18. Shoe sting enation Bulging and blisters

19. Leaf curling, rolling and twisting : curling of leaf lamina, leaves and petioles are twisted (tomato leaf curl, papaya leaf curl). Leaves may rolled downward or upward and become Britten (Potato and tobacco leaf roll).

20. Leaf curling Leaf rolling Twisting of leaves

21. Stem pitting bark scalding and cracking Small depressions on stem bellow bark (citrus tristeza ). Bark scalding and peeling (citrus psorosis ). Cracking of bark bellow the bud Union (citrus exocortis ).

22. Stem abnormalities in citrus tristeza Peeling and scalding of stem

23. Sterility Plant becomes completely sterile and unable to reproduce showing mosaic like symptoms on leaves .(pigeon pea sterility mosaic).

24. Necrosis in leaves and buds Brown red or reddish black concentric ring on leaves TMV Scattered necrotic patches or flecks of dead tissue may be produced on leaves TMV Necrosis may also appear on fruits seeds or tubers PVX, PVY Necrosis of bud groundnut bud blight and soybean bud blight.

25. yellowing

26. Excessive growth (hyperplasia) Proliferation of lateral buds or bunchy appearance to plant. Tumors on stem or other parts of plant(swollen shoot of cocoa). Leaf curl or leaf roll may be due to hyperplasia (chili leaf curl). Crinkling : maturation is uneven and causes furrowing or wrinkling like pattern ( urdbean leaf crinkle).

27. Leaf curl of chili

28. Hypoplasia Dwarfing : reduction in size compared to other organs (French bean yellow mosaic) Chlorotic : improper development of chlorophyll. Rose-tinted : sever reduction in inter-nodal growth (groundnut rosette virus). Other symptoms like mosaic, vain clearing, vain banding, streak are also due to hypoplasia .

29. Bunchy top of banana

30. Anatomical and histological symptoms One of the most important internal symptom is presence of inclusion bodies inside the host cells. Inclusion bodies are found in cell cytoplasm, most commonly found in epidermis and leaf hairs. Crystalline inclusion bodies. Amorphous inclusion bodies. Pinwheel type inclusion bodies. Necrosis of phloem tissues, epidermal cells, or fruits. There is aggregation and degeneration of mitochondria in virus infected cells.

31. Crystalline inclusion bodies Amorphous inclusion bodies

32. Loss of chlorophyll from mesophyll cells. Abnormal division of Cambium cells. Cell wall of virus infected plant is abnormally thickened. There is deposition of electron dance material between cell wall and plasma membrane. Proliferation of plasmadesmata . Some viruses causes disintegration of nucleolus.

33. Thank you...