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Introduction to Diseases

Introduction to Diseases. Introduction to Diseases. What disease is What causes disease Disease diagnosis Control Concepts. Introduction to Diseases. Disease = Abnormality. Horsfall and Cowling

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Introduction to Diseases

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  1. Introduction to Diseases

  2. Introduction to Diseases • What disease is • What causes disease • Disease diagnosis • Control Concepts

  3. Introduction to Diseases Disease = Abnormality Horsfall and Cowling "The term plant disease is properly applied to any deviation from normal growth or structure of plants that is sufficiently pronounced and permanent to produce visible symptoms or to impair quality and economic value." Stakman and Harrar Any disturbance of a plant that interferes with its normal growth and development, economic value, or aesthetic quality; a continuously, often progressively affected condition in contrast to injury, which results from momentary damage." Schumann Any disturbance brought about by a pathogen or a consistent environmental factor which interferes with normal manufacture, translocation, or utilization of nutrients Failure to reach full genetic potential due to the activities of another organism or environmental factor.

  4. Introduction to Diseases Disease = Abnormality Agrios “A malfunctioning of host cells and tissues that results from their continuous irritation by a pathogenic agent or environmental factor and leads to the development of symptoms. Disease is a condition involving abnormal changes in the form, physiology, integrity or behavior of a plant. Such changes may result in partial impairment or death of the plant or its parts.”

  5. Causes of Disease • Abiotic (Non-infectious) • Biotic (Infectious) Pathogen = an agent that causes disease

  6. Causes of Disease • Abiotic (non-infectious) • Extremes of temperature • Oxygen deficiency • Soil moisture • Air pollutants • Biotic (Infectious)

  7. Causes of Disease • Abiotic (non-infectious) • Extremes of temperature • Oxygen deficiency • Air pollutants • Soil moisture • Biotic (Infectious) • Bacteria - Mycoplasmas • Fungi - Nematodes • Mistletoes

  8. Fungi • Characteristics • Produce hyphae (structural unit) • Produce spores (reproductive unit) • Heterotrophic; obtain food from - • Dead organic matter (saprophytic) • From other living organisms (parasitic)

  9. Fungi • Characteristics • Produce Hyphae (structural unit) • Produce Spores (reproductive unit) • Heterotrophic • Beneficial • Decompose dead plants and animals • Important industrially • Mycorrhizae

  10. Bacteria • Characteristics • Single-celled • Microscopic • Lack chlorophyll Bacterial canker of cherry

  11. Seed Plants • Characteristics • Flowering plants • Most have chlorophyll • Establish root like haustorial connections with vascular elements of the host

  12. Mycoplasmas (MLOs) • Characteristics • Microscopic; smaller than bacteria • Single-celled; membrane rather than cell wall • Lack chlorophyll • Associated with yellows disorders Elm Yellows

  13. Viruses • Characteristics • Obligate, intracellular parasites • Non-living • Named according to symptoms produces

  14. Disease is the result of an interaction between a host, a potential pathogen, and the environment. If any one of these factors is missing then disease will not occur.

  15. Classifying Tree Diseases • Symptoms • Rots • Blights • Decays • Type of Pathogen • Fungal • Bacterial • Parts of Tree Affected • Roots • Stems • Foliar

  16. 1. Leaf spots - a foliage disease 2. Twig dieback - evidence of cankers and/or stress and decline 3. Mistletoe - a parasitic seed plant 4. Wilt - evidence of moisture deficiency, vascular wilt disease or root rot 5. Fruiting bodies of a canker fungus - signs of canker infections  6. Vascular streaking (internal) - evidence of vascular wilt disease 7. Branch canker at a branch stub 8. Heart rot (internal) and sporophore of a heart rot fungus at a broken branch stub 9. Sporophore of a butt-rot fungus at base of tree 10. Sporophores of a root rot fungus arising from a damaged root 11. Crown gall - a gnarled swelling ("tumor") caused by a bacterium 12. Severed root resulting from construction damage - site of entry for root and butt-rot  fungi 13. Nematode damage to small tree roots  lesions (upper) and galls (lower)

  17. Effects of Disease • Death • Growth Loss • Malformation • Predisposition Predisposition = the influence of the environment on the susceptibility of the host to disease

  18. Disease Diagnosis • Signs • Symptoms

  19. Clues Used in Diagnosis • Signs • Symptoms • Stand Conditions • Cultural Practices Related Circumstances are often extremely important in properly diagnosing a tree disease problem. For example, has the tree been exposed to severe or unusual weather conditions? Has there been a history of site disturbance such as building or road construction near the tree? What is the history of tree removal or thinning in the area? Has the tree been fertilized lately? What are the predominant soil and/or drainage features in the area? Have any chemical spills occurred in the area? Has a herbicide been used? Is there a source of an air pollutant nearby?

  20. Steps in Diagnosis • Identify the Host • Examine Site Conditions • Pattern of occurrence • Area affected • Weather conditions • Soils • Examine Affected Trees • Analyze Accumulated Information

  21. Kochs Postulates • Pathogen must ALWAYS be associated with disease in ALL diseased plants. There are no exceptions allowed. • 2. Pathogen must be isolated and established in PURE culture. This may be difficult with obligate parasites, but methodologies have been developed to fulfill this requirement even with obligate parasites. • 3. Inoculation of a healthy plant of the same variety must reproduce EXACTLY the same symptom(s). Inoculation must be of a healthy plant of the same species and cultivar. The symptoms must be reproduced essentially identical to the initial diseased plant. • 4. Pathogen must be reisolated from inoculated plant and its identity confirmed as the same as the original isolate. The organism recovered must be the identical to the original isolate. There are no exceptions.

  22. Types of Disease Control • Exclusion • Eradication • Protection • Chemicals • Cultural Practices • Host Resistance

  23. Cultural Practices – Examples • Modifying the environment • Choice of site • Reduce competition • Increase tree vigor • Avoiding tree wounding • Separating the tree and the pathogen • Utilizing the tree • Pathological rotations • Sanitation clauses

  24. Prevention Prevention is usually more effective, and cost efficient, than attempting to suppress the problem after its started.

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