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BASIC PLANT PATHOLOGY Topics 1.What is plant pathology 2.Definition of disease 3.Abiotic, biotic and decline diseases 4.Signs, symptoms and patterns 5.Mechanisms.

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Presentation on theme: "BASIC PLANT PATHOLOGY Topics 1.What is plant pathology 2.Definition of disease 3.Abiotic, biotic and decline diseases 4.Signs, symptoms and patterns 5.Mechanisms."— Presentation transcript:

1 BASIC PLANT PATHOLOGY Topics 1.What is plant pathology 2.Definition of disease 3.Abiotic, biotic and decline diseases 4.Signs, symptoms and patterns 5.Mechanisms of disease action 6.The disease triangle, square and tetrahedron 7.Classification of organisms 8. Organisms causing biological diseases 9. Pathogen/insect relationships


3 1. What is plant pathology – the study of the organisms and environmental factors that cause diseases in plants, mechanisms by which they cause disease, and methods of managing diseases and reducing damage. 2. Definition of disease - sustained physiological and structural damage to plant tissues caused by biological and non-biological agents ending sometimes in plant death.

4 TREEYOU Athlete’s foot fungus Skin diseases Ozone Heart rot Cankers Foliage diseases Vascular system diseases – Dutch Elm disease Root diseases

5 3. Biotic, abiotic and decline diseases Biological – fungi, bacteria, etc. non-biological (abiotic) decline (combination – distinct causes may be unknown).

6 Non-biological agents - excesses of temperature and moisture, nutrient deficiencies or excesses, air pollution, etc.

7 4. Signs, Symptoms and Patterns a. Signs - indications of presence of disease causing organism – e.g., fruiting body or mycelium of fungi b. Symptoms - change in host - exudations, resinosis, necrosis (death of tissue or tree), hypotrophy (dwarfing), hypertrophy (overgrowths - galls, witches brooms). c. Patterns – random – biotic agents - systematic - abiotic


9 Tar spot on maple leaf caused by a fungus- Random pattern

10 Iron deficiency – abiotic – systematic pattern

11 How do we establish that fungi caused the observed disease Rules of proof “Koch's postulates” i.Establish constant association of organism and disease symptoms. ii.Isolate organism and grow in pure culture. iii.Inoculate healthy plant and produce disease symptoms iv.Re-isolate organism.

12 5.Mechanisms of disease action Production of enzymes (pectinase, cellulase) Toxins Hormones (giberellin) Physically plugging conducting tissues Nutrient competition

13 6. The disease triangle - plant, pathogen, and environment


15 7. Classification of organisms


17 Tree of Life

18 Classification of fungi (Fusarium solani – important plant pathogen) Domain- EukaryaEurarya Kingdom- FungiFungi Phylum- ----mycotaAscomycota Class- ----mycetesEuascomycetes Subclass- ----tidaePyrenomycitdae Order- ----alesHypocreales Family- ----aceaeHypocreaceae GenusFusarium Speciessolani Forma specialesf. sp. gladioli Race 1

19 Classification of insects (Asian long-horned beetle) Domain- Eurarya Kingdom- Animalia Phylum- Arthropoda Class- Insecta SubclassPterygota Division Endopterygota Order- Coleoptera SuborderPolyphaga SuperfamilyChrysomeloidea FamilyCerambycidae SubfamilyLamiinae Tribe Monochamini GenusAnaplophora Speciesglabripennis 1

20 8. Organisms causing biological disease Fungi and fungus-like organisms Viruses, viroids, and prions Bacteria Phytoplasmas Nematodes Parasitic plants Protozoans

21 and fungus-like organisms


23 Fungi cause the greatest problems on woody plants because they have enzymes to break down cellulose and lignin. Bacteria and viruses more of a problem on soft tissued plants.

24 Perhaps a million species of fungi, but only 100,00 are known. 10,000 are plant pathogens

25 PhylumRole Fungus-like organism Oomycota Damping off, feeder (fine) root diseases True fungi ZygomycotaSaprophyte, endomycorrhizal fungi, few pathogens (storage molds) AscomycotaSaprophyte, ectomycorrhizal fungi, (Deuteromycota) foliage diseases, cankers, vascular wilts, fine root diseases, powdery mildews, stain fungi Basidiomycota Saprophytes, ectomycorrhizal fungi, stem and branch decays, structural root diseases, rusts

26 FEATURES OF FUNGI AND FUNGAL-LIKE ORGANISMS Phylum Features Hyphae Cell walls Spores Sexual Asexual Oomycota no septa glucans/cellulose Oospores zoospores (fungal-like) TRUE FUNGI Zygomycota no septa glucans/chitin Zygospores sporangiospores Ascomycota septa glucans/mannans Ascospores conidia Deuteromycota septa glucans/mannans None conidia Basidiomycota septa glucans/mannans Basidiospores conidia, (with (rarely) clamps)

27 Features of fungi The vegetative body of fungi is the mycelium (made up of thread-like hyphae – with and without septa) which grow through or on substrates. Fungi disperse widely by spores which can be either asexual or sexual. The most commonly produced spores are asexual conidia or conidiopsores. Other asexual spores are sporangiospores. Sexual spores include zygospores, ascospores and basidiospores; they are produced in fruiting bodies. Spores can be airborne, spread by rain splash or water or by insects, other animals and humans. Oomycota were once included in the Fungi but are now considered to be fungal-like organisms. Oomycota have asexual spores (zoospores) and sexual spores (Oospores). Many fungi have resting stages - chlamydospores or sclerotia



30 Nectria perithecia Ascomycota Peziza apothecia


32 Nectria Canker – Ascomycota

33 Ascomycete Fungus- Tar spot on maple leaf

34 Deuteromycete fungus – Penicillium conidia

35 Basidiomycete hyphae showing clamp connections. Also associated yeast cells and bacteria Basidiomycete hyphae decaying wood cells – clamp connections and Ca oxalate crystals

36 Basidiomycete fungus – Armillaria mushroom

37 Basidiomycete fungus – conk or fruiting body

38 White Pine Blister Rust – Basidiomycota


40 Other Pathogens Viruses, viroids, and prions Bacteria Phytoplasmas Nematodes Parasitic plants Protozoans

41 Viruses – protein coat and nucleic acid Viroid – low MW RNA Prion – infectious protein molecule Viruses, viroids, and prions

42 Viruses and viroids Needs a vector –Insects –Nematodes –Grafting or vegetative propagation Can move through plant in phloem or xylem, or stay localized in foliage Can become part of plant genome

43 Symptoms Foliage streaking, spotting, mottling Brooms or rosettes Growth reduction No symptoms

44 Camelia mosaic virus

45 Bacteria 1-celled prokaryotes with a cell wall Rods (bacilli), spirals, or spherical (cocci) Easily exchange genetic material on plasmids

46 Symptoms Bacteria cause disease by enzymes that digest cell walls, toxins, or tumors Typical symptoms are: –Water soaking –Wetwood –Shoot blight –Bleeding cankers –Galls

47 Bacterial Wetwood Very common on elms and poplars Caused by anaerobic bacteria in the xylem following wounding and wound closure May prevent decay fungi from colonizing

48 Crown Gall Caused by Agrobacterium tumifaciens, a soil bacterium Usually occurs at the soil line, but sometimes on aerial parts Requires wounding for infection Galls interfere with nutrient and water flow Used in genetic engineering – can insert DNA into plant genome

49 Elm bacterial gall

50 Important genera of bacteria Causing plant diseases Pseudomonas Xanthomonas Agrobacterium Bacillus Clostridium Streptomyces Bacterial leaf spot

51 Phytoplasmas Also called MLO’s, or Mycoplasm-like organisms Like bacteria without cell walls Cannot be cultured apart from the host

52 Symptoms Infect phloem and cause a systemic, lethal disease Causes elm yellows, X disease of cherry, coconut lethal yellowing, and others Symptoms: yellowing, epinasty, witches brooms, defoliation

53 Elm Yellows – Phytoplasma disease

54 Nematodes Worm-like animals in Phylum Nemahelminthes Various parasitic habits Usually in the soil or on roots, more of an issue in agriculture " If all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable..." -N.A. Cobb, 1914 -N.A. Cobb, 1914

55 Pine Wilt Nematode Bursaphelenchus xylophilus, vectored by Monochamus sp. (Cerambycidae) Introduced to Asia from North America

56 Root nematode Pine wilt nematode symptoms Pine wilt nematode

57 Mode of Action Plant parasitic nematodes have a stylet to pierce plant cell walls Cause injury by feeding, toxins Vectors of other diseases Contributing factors in declines Indirect damage

58 Parasitic Plants Evolution towards parasitism has occurred at least 8 times in the flowering plants. Many are in the order Santalales: Loranthaceae – leafy mistletoes Santalaceae – root and stem hemiparasites Viscaceae –Phoradendron – leafy mistletoes –Arceuthobium – dwarf mistletoes

59 True Mistletoes Phoradendron sp. - –Common on oaks – South of 40-45 lat. –Cause water stress, usually not lethal –Spread by birds

60 True mistletoe on oak in California

61 Dwarf Mistletoes Arceuthobium spp. –Host-specific –Conifer hosts –Dioecious –Sticky seeds spread by birds or forcefully ejected from plant

62 Dwarf mistletoe

63 Symptoms Parasitic plants are usually visible Brooming Galls Reduced growth

64 Protozoans such as phytoflagellates can parasitize milkweed, tomato, onion and chive plants.

65 9. Insect/Pathogen relationships a. Virus spread by plant hoppers, aphids b. Fungi spread by: bark beetles – Dutch elm disease fungus wood wasps (Sirex) – Hematostereum c. Nematodes spread by bark beetles – Pine wilt disease d. Bark beetles and root diseases are closely associated

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