Master Gardener - Plant Pathology

Transcription

1 Master Gardener - Plant Pathology How do I enroll in the online course? 1. Go to and look to the top right to find a login box. If you do have an account then log in with your username and password If you do not have an account, click on Create new account and fill in the information requested. You will receive an confirming the account creation within an hour or so. Follow the instructions in the in order to enable the account. If you do not get a confirmation please learnonline@ag.tamu.edu for help. After you have logged in look for the search box and type in the course name and click on the search button. 4. Then click on the title of the course to enroll. Enrollment Key: MGPP16 How do I come back to the course? Once you are enrolled in a course it will appear on a list under My Courses on the left side of your screen the next time you log in. You can then click on the course title to go back to any part of the course. Where can I get help and assistance? For questions related to the course content or structure contact Dr. Kevin Ong, kevo@tamu.edu. For technical assistance contact our help desk: learnonline@ag.tamu.edu

2 Extension Plant Pathology PLPA MG2 Master Gardener Training supplemental General Principles in the understanding of Plant Pathology The following are useful concepts in the field of plant pathology. They are limited to generalizations which apply to many or all groups of diseases. A. Etiology (cause) 1. Disease results from the continued irritation of plant by a living or nonliving agent. 2. Effects of microorganisms on higher plants are modified by environment. 3. Fungi are the major microorganisms responsible for disease. 4. The diagnosis of disease is based primarily on signs and symptoms. 5. Each species of plant is subject to its characteristic diseases. 6. Most diseases of economic plants have already been correctly diagnosed. 7. Unfavorable environments and genetic constitutions may cause nonparasitic disease. 8. Resistance to a specific disease is more common than susceptibility. 9. Species of pathogens exist in many physiological forms. 10. Pathogens commonly adapt themselves to resistant plant varieties. 11. The closer the genetic relation between hosts, the more similar (or closely related) their pathogens. B. Importance Several pathogens have the potential to destroy any crop but rarely do so. 13. Diseases reduce yield and quality of crop. 14. Diseases increase the variability and cost of crop production. C. Symptomology 15. Symptoms of disease are characteristic for different causal agents. 16. Some infections cause no recognized symptoms. 17. Parasites may increase the local or general growth of their host. 18. Infections and injuries increase plant respiration and permeability. 19. Fungi, bacteria, and nematodes usually cause localized infections. Viruses usually cause systemic infections. 20. Symptoms may be systemic, even if the pathogen is localized. Master Gardener Training (ONG) Some Principles of Plant Pathology Page 1 of 2

3 Master Gardener Training (ONG) Some Principles of Plant Pathology Page 2 of 2 D. Life History 21. The dormant stage of pathogens is more resistant to environment than the active stage. 22. Some pathogens have cycles requiring an alternate host. 23. Most pathogens can be cultured on nonliving substrata. 24. Most fungi and nematodes enter the plant actively, whereas bacteria and viruses enter passively. 25. The dispersal of pathogens is usually passive, but may be active and may be aided by vectors. 26. Principle vectors or pathogens are wind, water, arthropods, and man. 27. Specific pathogens enter through specific sites and colonize specific tissues. 28. Soil and plant debris are major reservoirs of plant pathogens. 29. Systemic infections increase at a slower rate than local infections. E. Predisposition 30. Resistance to a specific pathogen is more common than susceptibility. 31. Plants may increase or decrease in susceptibility with age. 32. High nitrogen fertilization commonly favors disease whereas, high potassium fertilization commonly reduces disease. 33. Several minor nutrients may be decisive for specific disease situations. F. Epidemiology 34. Pathogens increase more rapidly in pure stands than in mixed stands of plants or with rotation of crops. 35. Most fungi and bacteria require free moisture for the initiation of infection. 36. Major sources of free water are rain, dew, guttation water, and irrigation water. 37. The optimum temperature for most diseases is about 25 C(77 F). 38. Alternating light and darkness are usually necessary for normal disease development. 39. The effect of the environment is most critical during penetration of the plant. 40. Pathogens are typically more tolerant of extremes in heat or cold than are the plant host. G. Control 41. All knowledge of factors affecting disease has potential value in control. 42. Control of disease is usually directed at inhibition of the pathogen. 43. Control practices may be classified under exclusion, eradication, protection, immunization, and therapy. 44. Treatments which are therapeutic to one pathogen may predispose to another. 45. Protective measures become less effective with increasing inoculum potenti The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

4 Extension Plant Pathology PLPA MG3 Master Gardener Training supplemental GLOSSARY OF PLANT PATHOLOGY TERMS Adapted from several sources (including Plant Pathology 4 th Ed. GN Agrios) Abiotic disease: A disease caused by a nonliving factor (i.e., hail, cold, nutrient, etc.) Anthracnose: A necrotic and sunken ulcer-like lesion on the stem, leaf, fruit, or flower of the host plant caused by a fungus. Biotic disease: A disease caused by a living organism (i.e., fungus, virus, etc.) Blight: General and extremely rapid browning of leaves, branches, twigs, and floral organs resulting in their death. Usually young growing tissues are affected. Canker: Generally a dry, discolored, sunken, or cracked area on a stem, branch, or trunk. A canker generally has a distinct border between diseased and healthy tissue whereas a rot does not. Cankers may be caused by pathogens or by injuries. Chlorosis: Yellowing or whitening of normally green leaves. May be due to a virus, nutrient deficiency, lack or oxygen in a waterlogged soil, alkaline soil, or other factors. Damping off: The rapid death and collapse of very young seedlings in the greenhouse or field. Common damping-off pathogens include the fungi Pythium, Rhizoctonia, Fusarium, and Phytophthora. Decline: Poor growth of plants; leaves small, brittle, yellowish, or red; some defoliation and dieback commonly is present. Dieback: Extensive death of twigs beginning at the tips and advancing toward the bases. Dry rot: Disintegration of fruits, tubers, roots, or stems by fungis without release of liquids (see soft rot). Enation: Malformation or overgrowth of leaves, petioles, or flowers, induced by certain viruses. Host range: The various kinds of plants that may be attacked by a parasite. Hypha (pl.= hyphae): Thread-like structure that constitutes the body (mycelium) of a fungus. Leaf spot: Discrete lesions on host leaves consisting of dead and collapsed cells. Mollicute: Bacterium without a cell wall. This group includes phytoplasmas and spiroplasmas which infect the phloem (food-conducting tubes) of plants. Master Gardener Training (ONG) Glossary supplemental Page 1 of 2

5 Master Gardener Training (ONG) Glossary supplemental Page 2 of 2 Mosaic: Leaf symptoms characterized by intermingled patches of normal and light green or yellowish color; generally viral. Mycelium (pl. = mycelia): A mass of hyphae that make up the body of a fungus. Necrosis: Death of plant parts which generally turn black or brown. Parasite: An organism living on or in another living organism (host) and obtaining its food from the latter. Obligate: Requires a living host (eg. Viruses, rust fungi, mildew fungi, plant parasitic nematodes) Non-obligate: can live on host or non-living material (eg. Most bacteria and fungi) Pathogen: An organism or agent (e.g., fungus, bacterium, nematode, virus, or viroid) capable of causing disease in a particular host or range of hosts. Pathogenesis: The sequence of processes in disease development from the time of infection to the final reaction in the host. Race: A genetically- and often geographically-distinct mating group within a pathogenic species. Ringspot: A circular area of chlorosis or necrosis with a green center; generally viral. Root rot: Decay of roots in a living plant; often caused by pathogenic fungi. Scab: Localized lesions on host fruit, leaves, tubers, etc., usually slightly raised or sunken and cracked, giving a scabby appearance. Sign: The appearance or evidence of the pathogen. Soft rot: Slimy softening and decay of fruits, roots, bulbs, tubers, and fleshy leaves; caused by fungi or bacteria (see dry rot). Symptom: The appearance of disease or injury. Witches' broom: Broom-like growth or massed proliferation caused by the dense clustering of branches of woody plants; caused by false mistletoes, fungi (rusts and Taphrinales), phytoplasmas, bacteria, viruses, and nematodes. Yellows: A plant disease characterized by yellowing and stunting of the host plant. The information given herein is for educational purposes only. References to commercial products or trade names are made with the understanding that no discrimination is intended and no endorsement by Texas A&M AgriLife Extension Service personnel is implied. Educational programs of the Texas A&M AgriLife Extension Service are open to all people without regard to race, color, sex, disability, religion, age, or national origin. The Texas A&M University System, U.S. Department of Agriculture, and the County Commissioners Courts of Texas Cooperating

6 Extension Plant Pathology PLPA MG5 The logical steps in evaluating plant problems. Plant is exhibiting ABRMAL symptoms. EVALUATE INQUIRY or PROBLEM Is the problem(s) described or observed on the plant due to normal plant development for that particular time of the year? There is a likelihood of DISEASE PROBLEM INSECT PROBLEM Refer to an entomologist. Are there insects observed on the plant? Is the damage consistent with probable insect attack? TE: Presence of insects does not always mean that insects are the root cause of a plant problem Probably T insect problem. Are there signs of the pathogen(s) on damaged areas? Pathogen(s) not observed. IDENTIFY type of pathogen (fungi, bacteria, nematode) Is damage observed consistent pathogen attack? PROBABLY BIOTIC AGENT ENLIST help of the Texas Plant Disease Diagnostic Laboratory or the area plant pathologist. Is it or can it be identified? Is the damage scattered and is not uniformly distributed throughout tree and stand? PROBABLY ABIOTIC AGENT Abiotic problems are difficult to diagnose. Observed for obvious problems such as soil compaction, inadaptability of host, root disturbance. Obtain clues by understanding local environment conditions and query homeowner on tree management practices. Can problem be identified? PROBLEM IDENTIFIED! Consult Plant Disease Handbook and/or other resources for possible remedies or solutions. UNKWN MALADY Prescribe general care to maintain health of plant. Disease Diagnostic flow chart Page 1 of 1