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MG plant pathology

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MG plant pathology

  1. 1. Plant Pathology AN INTRODUCTION TO PLANTS AND THEIR DISEASES FOR MASTER GARDENERS MAUREEN THIESSEN AREA COMMERCIAL ORNAMENTAL SPECIALIST
  2. 2. Pathology Pathos – disease logos – study of Plant pathology is the study of diseases affecting plants What is disease? “The series of invisible and visible responses of plant cells and tissues to a pathogenic organism or environmental factor that result in adverse changes in the form, function or integrity of the plant and may lead to a partial impairment or death of plant parts or entire plant.” -Dr. Datnoff, Plant Pathologist, LSU AgCenter
  3. 3. Disease triangle ENVIRONMENT PATHOGEN SUSCEPTIBLE HOST Disease Environment
  4. 4. Diseases can be caused by abiotic and biotic factors… ABIOTIC Non-living causes of disease – disorders ◦ Air/Water pollution ◦ Nutrient or water imbalance ◦ Temperature stress ◦ Light stress ◦ Chemical or mechanical injury Can have effects on biotic disease factors BIOTIC Diseases are caused by other living organisms ◦ Fungus ◦ Bacteria ◦ Virus ◦ Nematodes ◦ Parasitic plants ◦ Algae and protozoa
  5. 5. Abiotic Factors Sunscald Phosphorus deficiency Drought Stress Sulfur damage from atmosphere Boron Toxicity
  6. 6. Abiotic Factors Calcium deficiency-induced blossom end rot Iron Deficiency Magnesium Deficiency
  7. 7. 2,4-D Damage Winterkill on turfgrass
  8. 8. Biotic Factors
  9. 9. Signs vs. symptoms A sign is any visible part of the actual pathogen ◦ Spores or fungal hyphae ◦ Bacterial streaming ◦ Parasitic plant parts ◦ Nematode Eggs A symptom is a manifestation of the damage caused by the pathogen ◦ Chlorosis, discoloration ◦ Wilting, stunting ◦ Distortion, loss of vigor
  10. 10. How do we confirm biological pathogens? Robert Koch – a German medical doctor and bacteriologist who discovered causal agents of anthrax, tuberculosis, and cholera. Developed steps for identifying and confirming causal disease agents, known today as Koch’s postulates: 1. 1. The suspected causal agent must be present in every diseased organism 2. 2. The suspected causal agent must be isolated from the diseased host organism and grown in pure culture. 3. When a pure culture of the suspected causal agent is inoculated into a healthy susceptible host, the host must reproduce the specific disease. 4. The same causal agent must be recovered again from the experimentally inoculated and infected host, and have the same characteristics as the organism in step 2.
  11. 11. Koch’s Postulates for Dogwood Anthracnose
  12. 12. Basic Disease Cycle Primary inoculum Secondary inoculum Infection
  13. 13. Where do diseases come from? Disease cycle begin when pathogen inoculum contacts an infectable site on a susceptible host. ◦ Can include fungal spores, bacterial cells, viruses, seeds ◦ Carried by wind, water, insects, humans, equipment
  14. 14. Inoculum Types and Locations of Survival of Plant Pathogens Between Crops
  15. 15. Dissemination of Plant Pathogens
  16. 16. Attachment, Penetration, Infection •Fungal inoculum lands on plant surface, and adheres either by present moisture or excretion of enzymes and mucilaginous substances •Bacterial and viral cells can be washed in by water droplets or insects
  17. 17. Attachment, Penetration, Infection •Bacterial and viral cells can be washed in by water droplets or insects •Nematodes enter directly or through root stoma
  18. 18. Effects of disease on vital processes Infection is the establishment and growth of pathogenic organisms and their parasitic effects in the host As pathogens obtain food and resources for themselves, they interfere with vital physiological functions Symptoms appear due to destruction of certain plant parts
  19. 19. Photosynthesis and Respiration Photosynthesis - process by which plants turn sunlight into energy ◦ Ability to create energy through photosynthesis is limited by: ◦ Leaf necrosis ◦ Spotting ◦ Defoliation ◦ Chlorosis (loss of green pigment) ◦ Destruction of enzymes involved in photosynthesis. Respiration – process by which living organisms burn energy to perform physiological processes. ◦ Rate is increase in diseased plants, reserves depleted more quickly as plants mobilize defense mechanisms Photo: Alan Windham
  20. 20. Effects on Translocation •Translocation is the movement of water and nutrients through the plant vascular system. •Pathogens interfere with translocation by: Rotting roots and stems, inhibiting their ability to absorb and transport water and nutrients Producing cankers, galls, and root knots that block transport
  21. 21. Effects on Translocation Clogging vascular tissue with growth (ex. Fusarium, Verticillium wilts) Damaging protective cuticle and integrity of cells, thereby increasing water loss
  22. 22. Effects on Growth and Development •Several viruses and some fungal pathogens affect plants by changing genetic material • Curling, mottling, stunting •Some pathogens destroy reproductive structures and seeds
  23. 23. Plant Defenses Plants encounter thousands of pathogens every day Infection fails to take place for most encounters due to: ◦ Lack of compatibility ◦ Structural Barriers ◦ Formation of toxins and other chemical defenses This is what causes plants to be resistant
  24. 24. Structural Defenses Many defenses keep pathogens from landing or sticking to plant tissue Preexisting ◦ Waxy cuticle – water film resistant ◦ Thick cell walls ◦ Leaf hairs ◦ Thorns
  25. 25. Structural Defenses Induced ◦ Plant cell receptors that recognize certain pathogens or their compounds can cause formation of defense structures to limit infection ◦ Cytoplasm changes ◦ Cell wall thickening and surrounding ◦ Formation of corky barriers or abscission layers ◦ Tyloses
  26. 26. Chemical Defenses •Plants produce substances that kill or repel pathogens or neutralize pathogen toxins •Phenolics and acids – “fungitoxic” and/or prevent spore germination •Phytoanticipins (antimicrobials) •Inhibit digestive pathogen enzymes •Tomatine and avenacin in tomatoes and oats have membraneolytic hydrolytic activity – break down pathogen •Can also be induced – plants have receptors for some pathogens that can elicit cascade of responses to wall off or kill infection
  27. 27. Fungal Symptoms
  28. 28. Types of Disease Pathogens Fungal Bacterial Viral Parasitic plants Nematodes
  29. 29. Fungal Diseases •Kingdom Fungi – Eukaryotic (nucleus containing) organisms that are heterotrophic, absorbing carbon fixed by other organisms (unlike plants) •Once considered to be plants without chlorophyll •Made up of hyphae – strands/branches that make up the body of the fungus – mycelium •Some are easily seen by their fruiting bodies, others remain hidden in the soil, some are unicellular (yeast)
  30. 30. Fungal Diseases •Nutrient uptake – Fungi secrete enzymes that digest material to be absorbed by the fungal hyphae. •Cause disease by maceration, cell destruction, and disruption of cell and whole-plant processes •Reproduce using spores housed in many different types of fruiting bodies •Fungal diseases spread by spores or transferal of hyphae
  31. 31. Some fungal life cycle examples P 437 vert basic rhizopus 447 plum pocket – diff kinds of spores may be involved P 462 septoria leaf spot like on tomato Rose powdery mildew p 451 Stem canker p 481 and pictures 477 Apple scap p 506 may be good replacement of one of the above Pp 606 wood rotting mushroom fungi Add your own pics of ganoderma
  32. 32. Apple Scab Venturia inaequalis
  33. 33. Powdery Mildew of Rose Sphaerotheca pannosa f. sp. rosae
  34. 34. Stem Cankers
  35. 35. Wood- Rotting fungi ex. Gannoderma
  36. 36. Fungal-like organisms Different kingdoms, but grow, reproduce, and cause disease much like Kingdom Fungus May have differences in cell wall structure, but still produce spores Myxo and Plasmoidium are more like masses of cytoplasm, not def cell wall. Oomycetes more like tru fungi ◦ Phytophthora, pythium, downy
  37. 37. Control of Fungal Diseases Plant diseases are nearly impossible to “cure” Control is mostly prevention-based Holistic Approach - Follow best management practices Use techniques that preserve plant health and minimize inoculation ◦ Resistant varieties ◦ Only accepting disease free plant material and seeds ◦ Minimize moisture , increase root aeration ◦ Destroy diseased material ◦ Sanitation of tools and environment Chemicals (synthetic and natural) can also be used, but should be in combination with above methods, and used preventatively as well
  38. 38. If have time, chemical control How some synthetics (chlorothalonil, etc. work_ How neem oil and other oils work specifically for fungi Consult ch 9
  39. 39. Bacterial diseases •Prokaryotic single-celled organisms – do not form structures •Are transported through the vascular tissue and intercellularly •Cause disease by multiplying and secreting toxins or clogging vascular tissues, maceration, cell destruction, toxins, and disruption of cell and whole-plant processes •Can also have DNA-altering activity
  40. 40. Infection •Bacterial cells can enter through wounds, stomata, hydathodes •Can be vectored by insects and nematodes as well •Cause spots, soft rots, wilts, cankers, galls,
  41. 41. Vascular Wilts ◦ Bacterial cells colonize vascular cells, destroying their integrity and limiting water and nutrient movement Affected xylem Affected phloem
  42. 42. Stem Cankers •Bacteria often enter through nodes or buds •Colonize and damage tissues •Causes girdling
  43. 43. Fireblight on Pear Erwinia amylovora
  44. 44. Galls ◦Bacteria parasitize the genetic and metabolic machinery of host ◦Bacterial cells enter through wounds and introduce own genetic material to host cell through a Ti plasmid. ◦These newly integrated genes cause host cells to synthesize materials useful only to bacteria, and to divide rapidly, forming galls, or tumors. ◦Similar to the establishment of cancer
  45. 45. Crown Gall Agrobacterium
  46. 46. Control Even more difficult to control than fungal diseases Many disease-causing bacteria survive in the soil - source of inoculum ◦ Sterilize media and soil, clean up and destroy diseased crops Holistic approach Resistant varieties Practice good sanitation: ◦ Frequently clean or change tools, especially in grafting and pruning ◦ Minimize production of wounds Copper compounds and antibiotics have had limited success
  47. 47. Viral Diseases •Viruses are considered non-living, obligate parasites •Much smaller than bacteria and fungi •Consist of a nucleic acid (genome) and protein covering, sometimes its own enzymes •Parasitizes the genetic and metabolic machinery of its host •Cause disease by disruption of normal cell functioning • Up- or down- regulate production of normal enzymes, compounds, and hormones, thus altering growth and appearance •Symptoms most often will consist of abnormal growth – mottling, mosaic discolorations, leaf stem and root malformations, stunting, streaking, distortion, etc.
  48. 48. Viral Symptoms
  49. 49. Infection and Spread •Viral particles enter through tiny wounds in cell walls. Nucleic acids are copied by viral or plant enzymes •Viral nucleic acid also codes for new viral “parts” – new protein coats, enzymes, and copies of genome. New viral particles are made •New particles are spread between cells (they are tiny enough) and through vascular tissues
  50. 50. Infection and Spread Can be spread by humans, animals, insects, fungi, mites, nematodes. Can remain in and spread through pollen and seed. Put figure 14-17 here
  51. 51. Eriophyid Mites and Rose Rosette
  52. 52. Thrips and Tomato Spotted Wilt Virus
  53. 53. Control of Viruses •Hardest to control •Resistant varieties •Limit insects and other disease-spreading organisms •Transgenic plants (TYLCV, tomato mottle begomovirus) •Virus free culture of apical meristem tips •No viricides exist
  54. 54. Other Plant Pathogens Parasitic Plants Examples include Dodder and Witchweed ◦ Produce flowers and seed but little to no chlorophyll ◦ Seeds exist in soil and germinate much like plants ◦ Strands wrap around stems and send fungus- like roots into plant tissues to harvest nutrients ◦ Usually controlled with herbicide
  55. 55. Nematodes Microscopic worms living freely in the soil Feed on roots with piercing stylet, inject saliva with enzymes, suck nutrients Enzymes in saliva cause degradation of plant tissues Causes root knots and lesions, root destruction and therefore typical ill-health symptoms above ground
  56. 56. Root Knot Nematode (Meloidogyne) •Cause extensive damage to many plant types (tomato, potato, carrot, peanut, dogwood •Causes galls, root stunting, and root necrosis •Control by rotation with resistant varieties, soil solarization or fumigation, nematicides.
  57. 57. Diagnosing 1. What is the host plant? 2. How many of the host plants are affected? 3. Is the pattern of damage random or uniform? 4. What plant parts are affected? 5. What are the signs and symptoms? 6. What recent activity has happened near the plants? Weather, temps, chemicals… 7. Cultural history (irrigation, fertilization). Has the soil been excessively wet? 8. Are there any wounds or mechanical damage?
  58. 58. Resources Extension ◦ County Agent ◦ Soil Plant, Pest Center ◦ search.extension.org
  59. 59. Resources Plant Pathology by George Agrios. 5th Edition, 2005 What’s Wrong With My Plant? And How Do I Fix It? by David Deardorff and Kathyrn Wadsworth. 2009

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