1. Biotic Diseases

2. They can be caused by: 1. Nematodes 2. Viruses 3. Bacteria 4. Parasitic higher plants 5. Fungi

3. Plant diseases caused by nematodes Soybean cyst nematodes Heterodera glycines Stem and bulb nematodes Ditylenchus dipsaci Nematodes are wormlike in appearance but taxonomically different from true worm. They live freely in fresh or salt waters or in soil and feed on microorganisms, plants and animals.

4. 1.Soybean cyst nematodes Heterodera glycines Plant: Soybean Parasite: Heterodera glycines

5. Symptoms: The root system of the infected plants appears smaller with fewer bacterial nodules and clusters of cyst nematodes. Infected soybean are stunted and their leaves turn yellow and fall off early.

6. 2.Stem and bulb nematodes Ditylenchus dipsaci Plant: Stem and bulb of plants Parasite: Ditylenchus dipsaci

7. Symptoms: Infected bulb: Curled green leaves and the scales becomes softened, loose and pale gray in color. Infected bulb may be split and become malformed, odorless and light in weight. Infected tuber: lesions appear on the tuber as small brown blemishes. On the cut surface, the underlying tissues appear granular and spongy. The blemishes grow larger and the final stage is expressed by mummification of the tuber.

8. Plant disease caused by viruses 1.Diseases caused by Tobacco mosaic virus 6.Disease caused by Papaya ringspot virus 3.Diseases caused by hordeiviruses 4.Diseases caused by Lettuce mosaic virus 5.Disease caused by sugarcane mosaic virus 2.Diseases caused by Tomato mosaic virus

9. 1.Diseases caused by Tobacco mosaic virus Disease name: Mosaic virus Plant: Tobacco Pathogen: Tobacco mosaic virus

10. Symptoms: Various degrees of chlorosis, curling, distortion, dwarfing of leaves, flowers and entire plants.

11. 2.Diseases caused by Tomato mosaic virus Disease name: Mosaic virus Plant: Tomato Pathogen: Tomato mosaic virus

12. Symptoms: Leaflets may be long and pointed, sometimes shoestring-like. Internal browning of fruits.

13. 3.Diseases caused by hordeiviruses Disease name: Barley stripe mosaic virus (BSMV) Plant: Barley (Hordeum spp.), grain crops and wild grasses Pathogen: hordeivirus

14. Symptoms: Chlorotic spots, yellow-brown strips and sometimes dwarfing and necrosis of plants.

15. 4.Diseases caused by Lettuce mosaic virus Disease name: Mosaic virus Plant: Lettuce Pathogen: Lettuce mosaic virus

16. 4.Diseases caused by Lettuce mosaic virus Disease name: Mosaic virus Plant: Lettuce Pathogen: Lettuce mosaic virus

17. Symptoms: Mottling (yellowing of leaves), distortion and marginal necrosis of leaves, dwarfing of plant and failure to produce lettuce head.

18. 5.Disease caused by sugarcane mosaic virus Disease name: Sugarcane mosaic virus Plant: Sugarcane, other gramineae (corn, sorgum,…) Pathogen: Sugarcane mosaic virus

19. Symptoms: Pale patches and twisted distorted leaves. Necrotic and stunted stems.

20. 6.Disease caused by Papaya ringspot virus Disease name: Papaya ringspot virus Plant: Papaya Pathogen:Ringspot virus

21. Symptoms: Fruit: Dark green and slightly sunken rings with unpleasant taste. Yellow mosaic leaves with stunting of the plant.