plant disease development


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  • Subject: Prayer for your support. Sir/Madam, We are pleased to introduce ourselves as an NGO in the district of Dhubri and this Non Governmental Organization was established in 1997 by a few educated youths with a view to undertake awareness, training, Socio-economic development of all sections of people of this economically backward region of Assam and registered under the Societies Registration Act,XXI of 1860.(Regd. No.RS/DBR/250/A/106 of 1997-98) on 1998. We have started this CLINIC with an aim & objective to provide services of farming related problems faced by the farmers of this region.. Your valuable suggestion and co-operation is highly solicited for smooth running of the Plant Health Clinic. Yours faithfully (MOHAMMEDUL HAQUE,B.Sc.Agril.) General Secretary NE PLANT HEALTH CLINIC ( An Unit of Chilarai Krishi Bikash Samity) A.K.Azad Road,Dhubri-783301,Assam Ph-9864568410/03662234007/e-mail:
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  • good information especially on disease triangle model a great help indeed to my delivery of plant pathology concepts
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plant disease development

  2. 2. OBJECTIVE Be familiar with disease triangle Clarify the factors for successful disease development Identify stages in disease development
  3. 3. Outline  Disease Triangle  Factors for successful disease development 1) Properties of pathogen 2) Properties of host 3) Properties of environment  Stages in disease development 1) 2) 3) 4) 5) Inoculation Penetration Infection Growth and Reproduction Dissemination
  4. 4. Disease Triangle
  5. 5. Factors for successful disease development
  6. 6. Disease Triangle Three important components of plant disease :  Susceptible host  Virulent pathogen  Favorable environment For disease to occur all three of these must be present.
  7. 7. Disease Triangle
  8. 8. Factors for successful disease development
  9. 9. 1) Properties of Pathogen Level of virulence Adaptability Dispersal efficiency Survival efficiency Reproductive fitness
  10. 10. 2) Properties of Host Susceptibility Growth stage & form Population density & structure General health
  11. 11. 3) Properties of Environment Temperature Rainfall / Dew Leaf wetness period Soil properties Wind
  12. 12. Stages in Disease Development
  13. 13. Stages in Disease Development 1)Inoculation 2)Penetration 3)Infection 4)Growth and Reproduction 5)Dissemination of Pathogen
  14. 14. 1) Inoculation Inoculation : The arrival of pathogen on the host Inoculum  The pathogen (s) that land on the host or  Any part of the pathogen that can initiate infection
  15. 15. Types of inoculum Primary inoculum  An inoculum that survives the dormant period & caused the first infections Primary infections  Infection caused by primary inoculum Secondary inoculum  An inoculum produced from primary infections Secondary infections  Infection caused by secondary inoculum
  16. 16. Landing or Arrival of inoculum  Most is carried by wind, water, insects  Only a small number actually lands on susceptible plants  Vector born pathogens are much more efficient since the vectors have an attraction for plants  E.g:     Germination of spores and seeds (fungus) Hatching of nematode eggs Attachment of Pathogen to Host (virus and bacteria) Recognition Between Host and Pathogen (Pathogen recognize the host)
  17. 17. 2) Penetration The initial invasion of a host by a pathogen: 1. Direct Penetration 2. Penetration Through Natural Openings 3. Penetration Through Wounds
  18. 18. Direct penetration 1)Direct Penetration  Direct with haustoria  Direct, subcuticular only  Direct intercellular mycellium  Direct, intercellular mycellium with haustoria  Direct with appressorium (A), penetration peg (PP) and intracellular mycelium (IM)
  19. 19. Direct penetration The most common type of penetration by fungi and nematodes and the only type by parasitic plants Fungi use a fine hyphae produced by a spore or mycelium or penetration peg produced by an appressorium This is formed at the point of contact with the host
  20. 20. Direct penetration The penetration is through mechanical force and softening of the cell walls by an enzyme Most fungi form an appressorium at the end of the germ tube Then a penetration peg emerges from the flat surface of the appressorium and pierces the cuticle and cell wall
  21. 21. Direct penetration The peg grows into a fine hyphae then reaches a normal diameter once it is inside the cell As in the case of apple scab, the fungus penetrates only the cuticle and stays between the cuticle and the cell wall Parasitic plants also penetrate the same way
  22. 22. Direct With Haustoria
  23. 23. Direct, subcuticular only
  24. 24. Direct, Intercellular Mycelium
  25. 25. Direct, Intercellular Mycelium with Haustoria
  26. 26. Direct with appressorium (A), penetration peg (PP) & intracellular mycelium (IM)
  27. 27. 2)Penetration Through Natural Openings Stomata Lenticels (opening on fruits, stems and tubers –filled with loosely connected cells – allow the passage of air) Hydathodes (permanently open pores at the margins and tips of leaves)
  28. 28. 3) Penetration Through Wounds Through various types of wounds Natural cracks between main and lateral roots Openings made by fungus
  29. 29. 3) Infection Establishment of pathogen with vulnerable cells or tissues of the host and obtain the nutrients from them Successful infection will produce symptoms
  30. 30. Incubation period : The time interval between inoculation and the appearance of disease symptoms Latent infection : The state in which a host is infected with a pathogen but does not show any symptoms
  31. 31. 4) Growth and Reproduction The pathogen will grow and multiply within the infected host. Fungi – spores Viruses – replicated by the cell Nematodes – reproduce by means of eggs 4. GROWTH & REPRODUCTION
  32. 32. 5) Dissemination of Pathogen  Pathogens are disseminated by several ways:  By air  While airborne – spores touch wet surfaces – get trapped – air movement stops / rains – washed out  From the air – brought down by rain drops  Winds also helps spreading by blowing away rain splash droplets containing pathogens
  33. 33.  By water  Pathogens in the soil – dissemination by rain / irrigation water that moves on the surface / through soil  By Insects, Nematodes & other Vectors  Transmitted by insects during feeding, movement from plant to plant  Nematodes can also transmit virus internally
  34. 34.  By Seed and Transplanting process  Transported to other fields  Are sold and transported to other areas  By human  Through handling of diseased and healthy plants  Tools (pruning shears)  Transporting contaminated soil on their feet / equipment  Contaminated container  Using infected seed / nursery stock