Nature of Damage and Economic Importance of Plant Parasitic Nematodes

1. Nature of Damage and Economic Importance of Plant Parasitic Nematodes Walia CCSHAU

2. Direct damage Walia CCSHAU

3. Mechanical damage by migratory nematode Walia CCSHAU

4. Induction of special feeding sites by sedentary nematodes Walia CCSHAU

5. Induction of special feeding sites by sedentary nematodes Walia CCSHAU

6. Factors governing direct damage Walia CCSHAU

7. Nematode interaction with other pathogens • 1 m3 of highly fertile field soil may contain • 3 x 1014 bacterial cells (300 g) • 5 x 108 protozoa (39 g) • 1 x 107 nematodes (12 g) • fungi (400g) • Biotic interactions of two types • Disease complexes (Role of nematodes?) • Antagonistic effect of other nematodes on nematodes (Biological control of nematodes) Walia CCSHAU

8. Indirect damage Walia CCSHAU

9. Nematodes as vectors of other pathogens • Fungal and bacterial propagules carried externally • Tundu disease of wheat • Cauliflower disease of strawberry • Virus particles carried internally • PPNs belonging to order Dorylaimida Walia CCSHAU

10. Virus transmission by nematodes • First reported by Hewiitt, Raski & Goheen in 1958 reported Fanleaf grapevine virus by Xiphinema index on grapes • Nematode vectors • Dagger nematode, Xiphinema • Needle nematode, Longidorus • Stubby root nematode, Trichodorus, Paratrichodorus Walia CCSHAU

11. Virus types • NEPO – nematode transmitted polyhedral viruses by Xiphinema and Longidorus e.g., Grapevine fanleaf virus, Tomato ringspot virus • NETU or TOBRA – Nematode transmitted tubular viruses or Tobacco rattle virus e.g., Pea early browning virus, Tobacco rattle virus • Specificity of Retention • X. index transmits GFLV but not Cherry leaf roll virus Walia CCSHAU

12. Steps involved in transmission of viruses • Acquisition • Nematodes become viruliferous by feeding on infected plants, all juveniles and adults can acquire viruses • Retention • Selectively adsorbed on cuticular lining of stomodaeum • Sites of retention vary among genera • Virus particles shed off at moulting • Can be retained for weeks • Dissociation • Oesophageal gland secretions dislodge virus particles • Inoculation Walia CCSHAU

13. Sites of retention of viruses Walia CCSHAU

14. FAQ Why tylenchids do not transmit viruses? Walia CCSHAU

15. Economic Importance of a PPN Walia CCSHAU

16. Crop loss estimation methods • Nematode populations not uniformly distributed in a field • PPNs occur as polyspecific communities within a field • Involvement of PPNs in disease complexes • Estimates based on avoidable loss • Comparison of field plots treated with nematicide v/s untreated plots Untreated Treated Walia CCSHAU

17. Estimated annual yield losses due to PPNs world-wide Walia CCSHAU

18. Estimated annual yield losses due to PPNs world-wide Loss % • Life sustaining crops 10.7 (Primary food source) • Economically important crops 14.0 (Commercial crops) • Developing countries 14.6 • Developed countries 8.8 • Overall average 12.3 Monitory loss based on 1984 production figures and prices = US$ 77billion Walia CCSHAU

19. Losses in USA (1971) Walia CCSHAU

20. Estimation of losses in India, 1969 Walia CCSHAU

21. Estimation of losses in India - 1999 • Oilseeds – 5% • Pulses – 8% • Sugarcane – 10% • Fruits – 10% • Vegetables – 12% • Total monitory losses - Rs 24,200 crores/year (Seshadri & Gaur, 1999) Walia CCSHAU

22. Ten major genera of PPNs • Root-knot nematodes, Meloidogyne spp. • Root-lesion nematodes, Pratylenchus spp. • Cyst nematodes, Heterodera spp. • Stem & Bulb nematode, Ditylenchus spp. • Potato cyst nematode, Globodera spp. • Citrus nematode, Tylenchulus sp. • Dagger nematode, Xiphinema spp. • Burrowing nematode, Radopholus spp. • Spiral nematode, Helicotylenchus spp. • Reniform nematode, Rotylenchulus sp. Walia CCSHAU