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

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.

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

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

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

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

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

Iron deficiency – abiotic – systematic pattern

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.

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

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

7. Classification of organisms

DOMAINS AND KINGDOMS

Tree of Life

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

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

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

and fungus-like organisms

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.

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

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

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)

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

Nectria perithecia Ascomycota Peziza apothecia

Nectria Canker – Ascomycota

Ascomycete Fungus- Tar spot on maple leaf

Deuteromycete fungus – Penicillium conidia

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

Basidiomycete fungus – Armillaria mushroom

Basidiomycete fungus – conk or fruiting body

White Pine Blister Rust – Basidiomycota

OOMYCOTA LIFE CYCLE

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

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

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

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

Camelia mosaic virus

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

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

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

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

Elm bacterial gall

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

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

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

Elm Yellows – Phytoplasma disease

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, N.A. Cobb, 1914

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

Root nematode Pine wilt nematode symptoms Pine wilt nematode

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

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

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

True mistletoe on oak in California

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

Dwarf mistletoe

Symptoms Parasitic plants are usually visible Brooming Galls Reduced growth

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

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