Crop Protection Final Reviewer PDF

History of Plant Pathology & Early Significant Plant Diseases Plant Pathology in the 20th Century Introduction Early Developments Theophr...

History of Plant Pathology & Early Significant Plant Diseases Plant Pathology in the 20th Century Introduction Early Developments Theophrastus – father of botany, but believed that diseases were God’s wrath Descriptive Phase – discovery and dev’t of methodologies for growing, studying microbes Robigus - rust god of the Romans; special holiday for Robigus, the Robigalia Experimental Phase – design of tests towards answering basic pathology questions Mistletoe - Recognized as the First Plant Pathogen by Albertus Magnus Etiological Phase – proving the causes of plant diseases Spontaneous Generation – early thought on the generation of Plant Diseases The Search for Control of Plant Diseases – finding the means to control pathogens Biology & Plant Pathology in Early Renaissance & the 1800’s Thoullier - observed that ergotism/ Holy Fire spread via consumption of infected wheat in 1670 The Main Areas of Progress Robert Hooke - invented the (compound) microscope & discovered the “CELL” 1. Chemical Control of Plant Diseases Antonius van Leeuwenhoek – improved the microscope & discovered microorganisms Millardet (1885) – invented Bordeaux mixture Carl von Linne -Published “Systema Naturae,” in 1735; established binomial nomenclature of plants. 1913- development of organic mercury compounds for seed treatment Charles Darwin - published “The Origin of Species by Means of Natural Selection” in 1859 Alexander Fleming (1928) - discovered the antibiotic penicillin Pier Antonio Micheli - described many new fungi in 1729; contested spontaneous generation 1934 - the first dithiocarbamate fungicide (thiram) Needham – 1st to observe nematodes in 1743 1965 - the first systemic fungicide carboxin Tillet – in 1755, demonstrated how smut dust infected other wheat plants 1950 -Antibiotics, primarily streptomycin, used against bacteria Prevost – in 1807, concluded that smut spores gave rise to smut disease 1967 – tetracycline antibiotics control mollicutes & fastidious bacteria Anton deBary - proved that potato late blight was caused by a fungus in 1861–1863 Louis Pasteur – proved that microorganisms were produced from preexisting ones & that most infectious 2. Appearance of Pathogen Races Resistant to Bactericides & Fungicides diseases were caused by germs; established the “germ theory of disease” 1954 - few strains of bacteria were resistant to certain antibiotics Robert Petri - developed artificial nutrient media for culture of microorganisms (Petri dishes) Robert Robert 1963 - strains of fungal plant pathogens were were resistant to fungicides. Koch - who established “Koch’s postulates” 1970s - widespread use of systemic fungicides caused appearance of many resistant fungi Kühn - in the 1870s wrote the first book on plant pathology, “Diseases of Cultivated Crops, Their Causes & Their 3. Public Concern about Chemical Pesticides Control” Rachel Carson – wrote “Silent Spring” in 1962; about the dangers of polluting the environment with Discovery of the various plant pathogens poisonous chemicals Fungi 1960s – banning of mercury pesticides, DDT, chlorinated hydrocarbons 1st pathogen discovered to cause diseases 4. Alternative Controls for Plant Diseases Prevost(1807) -concluded that smut spores caused wheat smut; Early 20th century – discovery of SUPRRESSIVE SOILS Anton deBary (1861-1863) – proved that potato leaf blight was caused by phytophtora infestans Nematodes 1928 onwards – use of ANTAGONISTIC MICROBES starting with fleming’s penicillin Needham (1743) 1st to observe nematodes; root-knot nematode was 1st observed in cucumber root galls Early 1930s – discovery of CROSS PROTECTION (antagonism of strains of the same virus) Protozoan Myxomycetes 1963 – 1st CONTROLLED USE OF ANTAGONISTS; P. gigantea against H. annosum w/c causes Woronin (1878)1st observed myxomycetes w/c causes clubroot disease of cabbage root and butt rot of pines Bacteria Late 1980s -use of GENETIC ENG’G to induce resistance Burrill (1878) discovers that bacteria caused the fire blight disease of pear & apple; 1990s – discovery of SYSTEMIC ACQUIRED (OR INDUCED OR ACTIVATED)RESISTANCE; Erwin Smith discovers Agrobacterium tumefaciens as causal agent of crown root gall Actigard: 1st commercial synthesized plant defense activator Viruses 5. Interest in the Mechanisms by W/c Pathogens Cause Disease A. Mayer (1886) demonstrated the pathogenicity of leaf juices of tabacco w/ yellow mosaic; 1886- deBary concludes that fungi produce toxins that kill cells in advance Ivanowski (1982) demonstrated via filtration that bacteria was not the primary agent Beijerinck (1898) tobacco mosaic was caused by a “contagious living fluid” called virus. 1905 – L.R. Jones reports involvement of cytolytic enzymes in soft rot of vegetables Protozoa 1915 – Pectic enzymes were found to be significant in disease formation Lafont (1909) discovered protozoa in cells of latex plants 1934 – confirmation of toxin as cause of white halo around spots of wildfire disease Stahel (1931) discovered that protozoans infect coffee - wildfire disease caused by Pseudomonas tabaci Vermeulen (1963) proved that protozoans caused disease in coffee 1947 - Helminthosporium (Bipolaris) sp. w/c blighted oats was shown to produce victorin Mollicutes 1926 - E. Kurosawa showed that the excessive growth of rice seedlings infected with the Doi et.al. (1967) observed mollicutes in Japan fungus Gibberella could also be produced by treating healthy seedlings with sterile Viroids culture filtrates of the fungus. Diener (1971) 1st discovered viroids as the cause of potato spindle tuber disease 1939 - the growth regulator produced by the fungus was identified and named gibberellin.  1950s - numerous microbes plant pathogenic fungi and bacteria were shown to produce would take place and whether, therefore, control measures (fungicides) should be the plant hormone indoleacetic acid (IAA) applied. mid-1960s - agent of fasciation (leafy gall) disease of peas was shown to produce 1963 - Vanderplank through the book “Plant Diseases: Epidemics and Control,” cytokinin, and the symptoms could be reproduced by treating the plants with established epidemiology as an important and interesting field of plant pathology. kinetin, an animal derived cytokinin. 1970s & 1980s - the Agrobacterium tumefaciens was shown to induce crown gall disease Parasitism & Pathogenicity of many plants by introducing Transforming DNA in plant cells which parasite - organism that lives on or in some other organism and obtains its food from the latter causes unregulated production of cytokinin and IAA leading to tumors parasitism - The removal of food by a parasite from its host 6. The Concept of Genetic Inheritance of Resistance & Pathogenicity plant parasite - organism that becomes intimately associated with a plant and multiplies or grows at 1894 - Eriksson showed that cereal rust fungus Puccinia graminis has different biological the expense of the plant. races that are morphologically same but differ in pathogenicity to their host; some Pathogenicity - the ability of a pathogen to cause disease; ability of the parasite to interfere with one of them being attack wheat, but not the other cereals, such as oats and rye or more of the essential functions of the plant, thereby causing disease. 1902 -H. M. Ward recognized the necrotic defense reaction called the “hypersensitive symbiosis - both the plant and the microorganism benefit from the association. response.” Biotroph/obligate parasites - grow and reproduce in nature only in living hosts 1964 - Z. Klement and colleagues recognized that the hypersensitive response also nonobligate parasites - live on either living or dead hosts and on various nutrient media operates against bacterial plant pathogens semi-biotrophs / facultative saprophytes – non-obligate parasites that live most of the time or 1972 - similar necrotic or hypersensitive response was described in animals and was called most of their life cycles as parasites, but, under certain conditions, may grow saprophytically on dead apoptosis (= falling out) organic matter 1905 - Biffen reports that the resistance of two wheat varieties and their progeny to a rust necrotrophs/saprophytes - live most of the time and thrive well on dead organic matter fungus was inherited in a Mendelian fashion (Inherited Resistance) facultative parasites – nectrotrophs that attack living plants and become parasitic 1909 - Orton working with the Fusarium wilts distinguished among disease resistance, disease escape, and disease endurance (tolerance) 1911 - Barrus shows that there is genetic variability within a pathogen species; i.e., different pathogen races are restricted to certain varieties of a host species 1914 - Stakman et.al established that same races of a pathogen within a pathogen species differ in their ability to attack certain varieties. 1946 -H.H. Flor working with the rust disease of flax, showed that for each gene for resistance in the host there was a corresponding gene for avirulence in the pathogen and for each gene for virulence in the pathogen there was a gene for susceptibility in the host plant (gene-for-gene relationship). 1963 - Vanderplank suggests two kinds of resistance: vertical resistance (controlled by a few “major” resistance genes); strong but is effective only against one/few pathogen races horizontal resistance (controlled by many “minor” resistance genes); weaker but is effective against all races of a pathogen species. 1946 - E. Gaümann proposed that in many host–pathogen combinations plants remain resistant through hypersensitivity; i.e., the attacked cells are so sensitive to the pathogen that they and some adjacent cells die immediately and in that way they isolate or cause the death of the pathogen. 1960’s - in some cases, disease resistance is brought about by phytoalexins, Epidemiology of Plant Disease Comes of Age 1944 - Mills developed a table listing the duration of rain required at each temperature for apple buds, leaves, and fruit to become infected by the ever-present apple scab fungus. He and others then could use this information to predict whether infection I. Plant pathology Bacterial 26. Citrus canker Asia, Africa, Brazil, U.S. Caused eradication of millions of trees in A. Etymology - ""pathos"- suffering; "logos"- to study Florida in 1910s and again in the 1980s and B. Definition - It is the study of the organisms and of the environmental 1990s 27. Fire blight of pome fruits North America, Europe Kills numerous trees annually factors that cause disease in plants 28. Soft rot of vegetables Worldwide Huge losses of fleshy vegetables Phytoplasmal C. The science and art of plant pathology 29. Peach yellows Eastern U.S., Russia Historical, 10 million peach trees killed Science – studies plant pathogens; Art – application of the science 30. Pear decline Pacific coast states & Canada Millions of pear trees killed (1960s), Europe D. Objective - to prevent /minimize plant diseases not only to increase food production but also to Nematode diseases maintain the quantity and quality of the harvested fresh commodity until it reaches the consumer 31. Root knot Worldwide Continuous losses on vegetables and most other plants (M. incognita) E. Economic importance - 14.1% of the crops are lost to plant diseases alone, the total annual 32. Sugar beet cyst nematode Northern Europe, Continuous severe annual losses on sugar beets worldwide crop loss from plant diseases is about $220 billion. Western U.S. 33. Soybean cyst nematode Asia, N. & S. America Continuous serious losses on soy Examples of Severe Losses Caused by Plant Diseases Disease Location Comments F. Types of crop losses Fungal Reduction in yield 1. Cereal rusts Worldwide Frequent severe epidemics; huge annual losses 2. Cereal smuts Worldwide Continuous, although lesser, losses on all grains Losses from deterioration during storage, marketing or transport 3. Ergot of rye and wheat Worldwide Infrequent, poisonous to humans & animals (C. purpurea) 4. Late blight of potato Cool, humid climates Annual epidemics, Irish famine (1845–46) (P. infestans) - The amt of food lost daily is enough to feed the world's population. 5. Brown spot of rice Asia Epidemics, e.g., the great Bengal famine (1943) Reduction in quality of produce 6. Southern corn leaf blight U.S. Historical interest, epidemic 1970, $1 billion lost 7. Powdery mildew of grapes Worldwide European epidemics (1840s–1850s) Losses from produce contaminated with toxins that cause various disorders 8. Downy mildew of grapes U.S., Europe European epidemic (1870s–1880s) o Aflatoxin : produced by A. flavus in corn, sorghum; carcinogenic 9. Downy mildew of tobacco U.S., Europe European epidemic (1950s–1960s); epidemic in North America (1979) o Ochratoxin: a nnycotoxin produced by A. ochraceaus; causes cancer of the liver 9. Downy mildew of corn Philippines Loss can be as high as 95% amounting to over o Yellow rice toxins: formed by Penicillium spp.; caused several deaths in Japan P170M annually (P. philippinensis) 10. Chestnut blight U.S. Destroyed almost all American chestnut trees (1904– o Estrogenic factor in corn: produced by Fusarium graminearum; causes testes 1940) atrophy and enlarged and aborted uteri of female pigs 11. Dutch elm disease U.S., Europe Destroying American elm trees (1918 to present) 12. Pine stem rusts Worldwide Causing severe losses in many areas o Fumonisins: formed by Fusarium spp. in corn grains; caused esophageal cancer 13. Dwarf mistletoes Worldwide Serious losses in many areas 14. Coffee rust Asia, South America Destroyed all coffee in southeast Asia (1870s– Losses due to predisposition of host to attack by other pathogens 1880s)especially in Sri Lanka (Ceylon) since 1970 o Example: nematode injuries on roots serve entry for other pathogens present in South and Central America 15. Banana leaf spot or Sigatoka Worldwide Great annual losses (M. fijiensis) o Leaf pathogens weaken plants which can become a host for root-rotting pathogens 16. Rubber leaf blight South America Destroys rubber tree plantations o Severely-defoliated trees can be readily attacked by Armillaria mellea etc. 17. Fusarium scab of wheat North America Severe losses in wet years Viral Losses from increased cost of production and handling 18. Sugar cane mosaic Worldwide Great losses on sugar cane and corn o Cost of disease control 19. Sugar beet yellows Worldwide Great losses every year 20. Citrus tristeza (quick decline) Africa, Americas, Phil. Millions of trees being killed; in Batangas, Phil. o Cost of culling disease commodities 21. Swollen shoot of cacao Africa Continuous heavy losses 22. Plum pox or sharka Europe, North America Spreading severe epidemic on plums, peaches, o Cost of added processing time/techniques apricots 23. Barley yellow dwarf Worldwide Important on small grains worldwide 24. Tomato yellow leaf curl Mediterranean countries, Severe losses of tomatoes, beans, etc. Caribbean Basin, U.S. 25. Tomato spotted wilt virus Worldwide On tomato, tobacco, peanuts, ornamentals, etc. 26. Cadang-cadang disease Philippines 1.'t observed in 1918; have caused the country a loss of over $200M (caused by viroid) II. Plant diseases 2. Necrotic symptoms —protoplast, cell or tissue death e.g. blight, scorch, canker A. Concepts of plant disease 3. Hypoplastic symptoms —failure to differentiate/dev. e.g. stunting, chlorosis disease progresses over a period of time; injury is an instantaneous action 4. Hyperplastic symptoms — overdev’t of plant parts/organs e.g. gall formation a. Hypertrophy - Overdevelopment due to the increase in the size of cells - A physiological malfunctioning due to animate agents (Whetzel, 1929). b. Hyperplasia - Abnormal increase in the number of cells -deviation from normal growth or structure (Stakman & Harrar, 1957). v. Symptoms and Diseases -malfunctioning process caused by continuous irritation (Horsfall and Dimond). 1. Abscission — premature falling of leaves 24. Rusetting — a superficial brownish roughening of - interaction between an organism and its environment w/c results in abnormal changes in the 2. Blast —sudden death of young buds, inflorescence or fleshy organs due to the suberization of epidermal or organism" (Merril, 1980). young fruits. subepidermal tissues - malfunctioning of host cells and tissues that results from continuous irritation by a pathogen or 3. Bleeding— flow of plant sap from wounds. 25. Sarcody— abnormal swelling of the bark above an environmental factor and leads to the development of symptoms" (Agrios, 1998). 4. Blight — an extensive sudden, death of host tissues wounds due to the accum’n of elaborated food materials. 5. Blotch — large, irregular spots on leaves or fruits with 26. Savoying — the cupping or pocketing of parts of the necrotic injury of epidermal cells. leaf; underdevelopment of veins of leaf margins. B. Classification of plant diseases 6. Callus — overgrowth of tissue formed due to injury 27. Scab — slightly raised, ough, ulcer—like lesions i. According to affected plant organ (root, fruit, stem, foliage etc.) 7. Canker — sunken necrotic area with cracked border 28. Shot—hole - a perforated appearance of a leaf as the ii. According to symptom (spots, rusts, smuts, anthracnose, etc) 8. Chlorosis — yellowing but not due to light dead 9. Curling — abnormal bending/curling of leaves areas of local lesions drop out. iii. According to type of affected plant (vegetable, cereals, ornamentals, trees etc) 10. Damping off — rotting of seedlings prior to 29. Spot — a localized necrotic area also referred to as a iv. According to type of causal agent (biotic or abiotic) emergence/rotting of stem closest to soil lesion C. Common terms in plant pathology (last page) 11. Die-back — a drying backward from the tip 30. Streak or stripe — long, narrow necrotic lesions on 12. Etiolation — yellowing caused by inadequate light. leaves or stems. D. The Disease Triangle 13. Fasciculation/fasciation — clustering of roots, flowers, 31. Vein clearing— the leaf veins are translucent or pale fruits, or twigs around a common focus. while; the rest of the leaf is its normal color. 14. Flecks — extremely tiny spots on leaves, etc. 32. Virescence or greening— development of chlorophyll 15. Gumming/gummosis — oozing out of viscid gum in tissues or organs where it is normally absent. from wounds in bark. 33. Wilting — may be due to an infectious agent or to lack The length of each side is based on the optimal conditions for 16. Leak —exudation/ leak out of juices from soft—rotted of water. disease development (e.g. host is wrong age or resistant then portions. Wilting due to water- temporary and plant recovers upon HOST SIDE is small) 17. Mosaic — variegated patterns w/ defined borders. the application of enough moisture unless the drought is 18. Mottling— the variegation is less defined than mosaic prolonged and the plant dies. defused color boundaries. Wilting by an infectious agent - leads to death of the 19. Mummification — shriveled mummy of an infected plant unless controlled in time. fruit 20. Phyllody — sepals, petals, stamens, or carpels turn become leaf—like. 21. Pitting—depressions or pits on the surface of fruits, III. Plant disease diagnosis tubers and other fleshy organs; pocked appearance. 22. Rosetting —crowding of the foliage in a rosette. A. Symptoms of plant diseases (expressions by the suscept or host of a pathologic condition) 23. Rotting — the disintegration and decomposition of i. Primary vs. Secondary Symptoms (direct results vs. distant results) host tissue. ii. Localized vs. Systemic Symptoms (limited e.g. spots vs. generalized e.g. blight) dry rot - firm, dry decay soft rot - soft, watery decomposition. iii. Histological or Morphological Symptoms (internal vs. external) iv. General classification of symptoms 1. Plesionecrotic symptoms — pre-necrotic; before death e.g. wilting. B. Signs of Plant Diseases fungal diseases: mycelia, spores, fruiting bodies, etc. C. Koch's rules of proof of pathogenicity bacterial diseases: bacterial cells, bacterial ooze 1. The suspected causal agent should be present in every sample examined. nematode diseases: eggs, juveniles, adult nematodes 2. The suspected causal agent (bacterium, etc.) must be isolated & purified virus diseases: virus particles, inclusion bodies 3. Inoculated pure culture must reproduce the specific disease. viroid diseases: RNA fragments 4. The same causal agent must be recovered again infected host diseases caused by parasitic flowering plants: seeds and the plant itself i. 3 General Categories of Signs IV. Non-parasitic agents of plant diseases: Abiotic diseases (1) Vegetative structures (2) Reproductive structures o. Sonic— mass or cluster of spores Abiotic diseases or injury (absorption & storage) borne on short stalks 1. low temperatures 6. Injury caused by air pollutants p. Sporangium-enlarged tlp of hyphal Freezing injury — T< 0°c, ice crystals form w/in or in- mainly gases and particulates (soots, dusts, ashes) a. Acervulus — a mat of hyphae, branch that bear sporangiospores between cells Ethylene — essential plant hormone a. Felt— a densely woven mat of assoc. w/ a host, form lesions with q. Spore— general name for a single Chilling injury — T slightly above 0°c (