Introduction to Plant Pathology
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Questions and Answers

Who first observed myxomycetes that cause clubroot disease of cabbage?

  • Erwin Smith
  • L.R. Jones
  • A. Mayer
  • Woronin (correct)

    • What was discovered by Burrill in 1878 regarding bacteria?

  • They have no role in disease.
  • They cause fire blight of pear and apple. (correct)
  • They produce toxins killing plant cells.
  • They are responsible for crown root gall.

    • Which plant defense activator was the first commercial synthesized?

  • Agrobacterium
  • Actigard (correct)
  • Systemic acquired resistance
  • Pectic enzymes

    • What did Ivanowski demonstrate in 1982 regarding tobacco mosaic disease?

    <p>Viruses are the primary agents.</p> Signup and view all the answers

    Which of these pathogens was linked to the soft rot of vegetables in 1905?

    <p>Bacteria</p> Signup and view all the answers

    What significant enzyme was discovered in 1915 that contributes to disease formation?

    <p>Pectic enzymes</p> Signup and view all the answers

    What organism did Stahel discover infecting coffee in 1931?

    <p>Protozoa</p> Signup and view all the answers

    Which pathogen was shown to produce victorin that blighted oats in 1947?

    <p>Bipolaris sp.</p> Signup and view all the answers

    What is the term for the clustering of roots, flowers, fruits, or twigs around a common focus?

    <p>Fasciculation</p> Signup and view all the answers

    Which symptom is characterized by the leaf veins appearing translucent or pale while the rest of the leaf maintains its normal color?

    <p>Vein clearing</p> Signup and view all the answers

    What does virescence indicate in plant tissues?

    <p>Development of chlorophyll</p> Signup and view all the answers

    Which of the following is described as a pocked appearance due to depressions on surface tissues?

    <p>Pitting</p> Signup and view all the answers

    What characteristic defines wilting that is caused by an infectious agent?

    <p>Irreversible death of the plant</p> Signup and view all the answers

    What is the primary objective of plant pathology?

    <p>To prevent or minimize plant diseases</p> Signup and view all the answers

    Which type of disease caused the death of 10 million peach trees in the Eastern U.S. and Russia?

    <p>Peach yellows</p> Signup and view all the answers

    Which of the following regions experienced millions of pear trees killed due to pear decline?

    <p>Pacific coast states &amp; Canada</p> Signup and view all the answers

    What percentage of crops is estimated to be lost to plant diseases?

    <p>14.1%</p> Signup and view all the answers

    What economic loss is attributed to plant diseases annually worldwide?

    <p>$220 billion</p> Signup and view all the answers

    What is the condition characterized by the excessive swelling of the bark above an injury?

    <p>Sarcody</p> Signup and view all the answers

    Which nematode disease is known for continuous losses on soybeans in Asia and North & South America?

    <p>Soybean cyst nematode</p> Signup and view all the answers

    Which term describes the yellowing of plant leaves not caused by light deficiency?

    <p>Chlorosis</p> Signup and view all the answers

    Which disease caused continuous severe annual losses on sugar beets in Northern Europe and the Western U.S.?

    <p>Sugar beet cyst nematode</p> Signup and view all the answers

    What is the name for the localized necrotic area commonly referred to as a lesion?

    <p>Spot</p> Signup and view all the answers

    What type of diseases result in frequent severe epidemics and huge annual losses globally?

    <p>Fungal diseases</p> Signup and view all the answers

    Which phenomenon involves the rotting of seedlings prior to emergence?

    <p>Damping off</p> Signup and view all the answers

    What is a common type of crop loss caused by plant diseases?

    <p>Reduction in yield</p> Signup and view all the answers

    What condition results in large, irregular spots on leaves or fruits due to necrosis?

    <p>Blotch</p> Signup and view all the answers

    Which of these diseases is responsible for continuous losses on vegetables worldwide?

    <p>Root knot</p> Signup and view all the answers

    What symptom is characterized by a perforated appearance of leaves?

    <p>Shot-hole</p> Signup and view all the answers

    Which term refers to overgrowth of tissue formed due to injury?

    <p>Callus</p> Signup and view all the answers

    What term is used to describe the drying backward from the tip of a plant?

    <p>Die-back</p> Signup and view all the answers

    Which disease symptom involves extensive sudden death of host tissues?

    <p>Blight</p> Signup and view all the answers

    Which of the following terms denotes the sunken necrotic area with a cracked border?

    <p>Canker</p> Signup and view all the answers

    What type of resistance is characterized by being strong but effective only against one or a few pathogen races?

    <p>Vertical resistance</p> Signup and view all the answers

    Which plant defense mechanism involves the immediate death of attacked and adjacent cells to isolate the pathogen?

    <p>Hypersensitivity</p> Signup and view all the answers

    What did Mills develop in 1944 to predict infection by the apple scab fungus?

    <p>A table correlating rain duration and temperature</p> Signup and view all the answers

    Which of the following types of resistance is controlled by many 'minor' resistance genes and is effective against all races of a pathogen species?

    <p>Horizontal resistance</p> Signup and view all the answers

    Which disease caused the eradication of millions of trees in Florida during the 1910s and again in the 1980s and 1990s?

    <p>Citrus canker</p> Signup and view all the answers

    What component is suggested to contribute to disease resistance in some plants starting in the 1960s?

    <p>Phytoalexins</p> Signup and view all the answers

    What does the term 'plant pathology' refer to?

    <p>The study of plant diseases and their causes</p> Signup and view all the answers

    Which of the following elements is NOT associated with hypersensitivity as a plant defense mechanism?

    <p>Production of phytoalexins</p> Signup and view all the answers

    E.Gaümann's proposal in 1946 primarily related to which aspect of plant disease resistance?

    <p>Cellular responses to pathogen attack</p> Signup and view all the answers

    In the study of plant diseases, which aspect was significantly advanced with Mills' research?

    <p>Predicting infection risk based on environmental conditions</p> Signup and view all the answers

    Which of the following best describes systemic symptoms in plants?

    <p>Symptoms that manifest throughout the entire plant.</p> Signup and view all the answers

    What do plecionecrotic symptoms indicate in plant diseases?

    <p>They represent symptoms before the plant experiences cell death.</p> Signup and view all the answers

    What is a key component of Koch's postulates in proving pathogenicity?

    <p>The same agent must be isolated from multiple infected plants.</p> Signup and view all the answers

    Which of the following is classified as a sign of plant diseases caused by viruses?

    <p>Inclusion bodies</p> Signup and view all the answers

    How is dry rot characterized in plant pathology?

    <p>By firm and dry decay without moisture.</p> Signup and view all the answers

    What was the significance of the discovery made by Woronin in 1878?

    <p>He first observed myxomycetes related to clubroot disease of cabbage.</p> Signup and view all the answers

    Which advancement in plant disease understanding occurred in the 1990s?

    <p>Identification of systemic acquired resistance.</p> Signup and view all the answers

    Who was the first to demonstrate that fungi produce toxins, and in what year?

    <p>deBary in 1886.</p> Signup and view all the answers

    What was revealed about tobacco mosaic disease through the filtration experiments of Ivanowski in 1982?

    <p>A virus was responsible for its causation.</p> Signup and view all the answers

    Which agent did Erwin Smith identify as causing crown root gall?

    <p>Agrobacterium tumefaciens.</p> Signup and view all the answers

    In which year did Lafont discover protozoa in the cells of latex plants?

    <p>1909</p> Signup and view all the answers

    What significant finding was linked to the disease known as wildfire in 1934?

    <p>Toxins were confirmed to cause disease symptoms.</p> Signup and view all the answers

    Which pathogen was confirmed to be involved in the white halo around spots of wildfire disease?

    <p>Pseudomonas tabaci.</p> Signup and view all the answers

    Which type of resistance is generally seen to be weaker but effective against all pathogen races?

    <p>Horizontal resistance</p> Signup and view all the answers

    What is the primary mechanism through which plants achieve resistance according to E.Gaümann's 1946 proposal?

    <p>Hypersensitivity leading to cell death</p> Signup and view all the answers

    What did Mills develop in 1944 to enhance predictions of plant infection?

    <p>A table of rain duration and temperatures</p> Signup and view all the answers

    Which term describes the control of plant disease through the production of phytoalexins?

    <p>Induced resistance</p> Signup and view all the answers

    What is a primary characteristic of vertical resistance in plants?

    <p>Strong but effective against few races</p> Signup and view all the answers

    What is the primary characteristic of biotrophs or obligate parasites?

    <p>They only reproduce in living hosts.</p> Signup and view all the answers

    Which region was significantly affected by citrus canker, resulting in the eradication of millions of trees?

    <p>Florida</p> Signup and view all the answers

    The hypersensitive response in animals was later referred to as what?

    <p>Apoptosis</p> Signup and view all the answers

    What does the study of plant pathology primarily focus on?

    <p>Organisms and factors causing disease in plants</p> Signup and view all the answers

    During which decade were phytoalexins recognized to contribute to disease resistance in plants?

    <p>1960s</p> Signup and view all the answers

    What relationship is demonstrated by H.H. Flor's work with flax rust disease?

    <p>Resistance genes in hosts correspond to virulence genes in pathogens.</p> Signup and view all the answers

    Which disease is known for causing severe losses by killing numerous trees annually in North America and Europe?

    <p>Fire blight of pome fruits</p> Signup and view all the answers

    What term best describes pathogens that can live on either living or dead hosts?

    <p>Nonobligate parasites</p> Signup and view all the answers

    What study method did Mills and others utilize to predict infection by apple scab?

    <p>Environmental correlation</p> Signup and view all the answers

    Which of the following concepts differentiates disease endurance from disease resistance?

    <p>Endurance focuses on surviving after infection.</p> Signup and view all the answers

    What is a defining feature of facultative parasites?

    <p>They can shift to saprophytic growth when conditions are suitable.</p> Signup and view all the answers

    Who contributed to the understanding of genetic variability within a pathogen species?

    <p>Barrus</p> Signup and view all the answers

    What is the primary implication of the gene-for-gene relationship established by H.H. Flor?

    <p>Every resistance gene is matched with a virulence gene in pathogens.</p> Signup and view all the answers

    Which of the following accurately describes semi-biotrophs or facultative saprophytes?

    <p>They mostly live parasitically but can grow saprophytically under certain conditions.</p> Signup and view all the answers

    What concept refers to the resistance inherited from one or both parent wheat varieties to a rust fungus?

    <p>Inherited Resistance</p> Signup and view all the answers

    What condition is characterized by the yellowing of plant leaves not caused by light deficiency?

    <p>Chlorosis</p> Signup and view all the answers

    Which term describes the drying backward from the tip of a plant?

    <p>Die-back</p> Signup and view all the answers

    What type of abnormal plant tissue growth is formed due to injury?

    <p>Callus</p> Signup and view all the answers

    What is the term for extensive sudden death of host tissues caused by a pathogen?

    <p>Blight</p> Signup and view all the answers

    What symptom is described by large, irregular spots on leaves or fruits due to necrotic injury?

    <p>Blotch</p> Signup and view all the answers

    Which term refers to the localized necrotic area also known as a lesion?

    <p>Spot</p> Signup and view all the answers

    What phenomenon leads to the rotting of seedlings prior to emergence?

    <p>Damping off</p> Signup and view all the answers

    Which symptom is characterized by the formation of slightly raised, rough, ulcer-like lesions?

    <p>Scab</p> Signup and view all the answers

    What symptom involves the cupping or pocketing of parts of a leaf?

    <p>Savoying</p> Signup and view all the answers

    What term describes long, narrow necrotic lesions on leaves or stems?

    <p>Streak or stripe</p> Signup and view all the answers

    Who established the germ theory of disease?

    <p>Louis Pasteur</p> Signup and view all the answers

    What was the first dithiocarbamate fungicide developed?

    <p>Thiram</p> Signup and view all the answers

    What significant advancement occurred in 1965 in the field of fungicides?

    <p>Development of systemic fungicides</p> Signup and view all the answers

    Which scientist proved that potato late blight was caused by a fungus?

    <p>Anton deBary</p> Signup and view all the answers

    Which of the following provided evidence against spontaneous generation?

    <p>Louis Pasteur</p> Signup and view all the answers

    What was the primary focus of Kühn's book published in the 1870s?

    <p>Diseases of cultivated crops</p> Signup and view all the answers

    What was the primary finding of research conducted in the 1970s related to fungicides?

    <p>Pathogen races showed increased resistance to fungicides</p> Signup and view all the answers

    Which antibiotic was primarily used against bacteria in 1950?

    <p>Streptomycin</p> Signup and view all the answers

    What symptom is associated with the gumming or exudation of viscid gum from wounds in bark?

    <p>Gumming/gummosis</p> Signup and view all the answers

    What condition is primarily characterized by the oozing out of juices from soft, rotted portions of a plant?

    <p>Leak</p> Signup and view all the answers

    Which term refers to the phenomenon where the leaf veins appear pale while the surrounding leaf tissue remains normal?

    <p>Vein clearing</p> Signup and view all the answers

    Mosaic symptoms in plants are identified by what specific characteristic?

    <p>Defined variegated patterns</p> Signup and view all the answers

    What does the term 'mummification' refer to in plant diseases?

    <p>Shriveling of infected tissue</p> Signup and view all the answers

    What is the total annual economic loss attributed to plant diseases worldwide?

    <p>$220 billion</p> Signup and view all the answers

    Which disease resulted in the historical loss of 10 million peach trees?

    <p>Peach yellows</p> Signup and view all the answers

    What type of losses are associated with nematode diseases?

    <p>Continuous losses on vegetables and other plants</p> Signup and view all the answers

    Which plant disease is identified as causing severe annual losses on sugar beets in Northern Europe?

    <p>Sugar beet cyst nematode</p> Signup and view all the answers

    What is a primary objective of plant pathology?

    <p>To prevent and minimize plant diseases</p> Signup and view all the answers

    Which nematode disease is associated with continuous serious losses on soybeans in Asia and North & South America?

    <p>Soybean cyst nematode</p> Signup and view all the answers

    What percentage of crops are estimated to be lost to plant diseases?

    <p>14.1%</p> Signup and view all the answers

    Which of the following diseases is widely known for causing frequent severe epidemics globally?

    <p>Cereal rusts</p> Signup and view all the answers

    What is a significant economic impact of plant diseases mentioned?

    <p>Losses of approximately $220 billion</p> Signup and view all the answers

    Which disease is highlighted for killing millions of pear trees across multiple regions?

    <p>Pear decline</p> Signup and view all the answers

    What describes nonobligate parasites in relation to their hosts?

    <p>They can live on either living or dead hosts.</p> Signup and view all the answers

    The term 'hypersensitive response' in plants is characterized by which of the following actions?

    <p>A necrotic defense reaction to isolate pathogens.</p> Signup and view all the answers

    What relationship was established by H.H. Flor in regard to resistance in plants?

    <p>For each resistance gene in the host, there exists a corresponding gene for avirulence in the pathogen.</p> Signup and view all the answers

    What distinguishes semi-biotrophs from other parasite types?

    <p>They can act either as parasites or saprophytes under certain conditions.</p> Signup and view all the answers

    In context to plant resistance studies, Biffen's observations regarding wheat varieties introduced the concept of what?

    <p>Mendelian inheritance of resistance traits.</p> Signup and view all the answers

    Which term refers to the genetic variability within a pathogen species that affects its ability to attack host plants?

    <p>Pathogen races.</p> Signup and view all the answers

    Which of the following statements is true regarding necrotrophs?

    <p>They thrive on both dead organic matter and living hosts, especially when they become parasitic.</p> Signup and view all the answers

    Which aspect of plant disease resistance was assessed by Orton's research on Fusarium wilts?

    <p>The distinctions among disease resistance, disease escape, and disease endurance.</p> Signup and view all the answers

    What characteristic defines obligate biotrophs?

    <p>They require living hosts for their complete lifecycle.</p> Signup and view all the answers

    Which year did Z. Klement and colleagues recognize the hypersensitive response as a defense mechanism against bacterial plant pathogens?

    <p>1964</p> Signup and view all the answers

    What economic impact did the Southern corn leaf blight have in the U.S. during its epidemic?

    <p>$1 billion lost</p> Signup and view all the answers

    Which disease was primarily responsible for the Irish famine in the 1845–46 period?

    <p>Late blight of potato</p> Signup and view all the answers

    What type of toxin is produced by A. flavus in corn and sorghum?

    <p>Aflatoxin</p> Signup and view all the answers

    Which disease had a significant impact on the quality of produce during epidemics in Asia, particularly during the Bengal famine of 1943?

    <p>Brown spot of rice</p> Signup and view all the answers

    What is the primary region affected by the brown spot of rice?

    <p>Asia</p> Signup and view all the answers

    What was the main consequence of the chestnut blight in the U.S. from 1904 to 1940?

    <p>Loss of all American chestnut trees</p> Signup and view all the answers

    Which pathogen is responsible for the disease known as late blight?

    <p>P. infestans</p> Signup and view all the answers

    What kind of economic damage does downy mildew of corn cause annually in the Philippines?

    <p>P170 million</p> Signup and view all the answers

    Which type of toxin associated with downy mildew of tobacco is known for causing cancer of the liver?

    <p>Ochratoxin</p> Signup and view all the answers

    What kind of losses do cereal smuts cause globally?

    <p>Continuous, although lesser, losses on all grains</p> Signup and view all the answers

    What is indicated by the development of chlorophyll in tissues or organs where it is normally absent?

    <p>Virescence</p> Signup and view all the answers

    Which symptom is characterized by extreme clustering of plant parts around a common focus?

    <p>Fasciculation</p> Signup and view all the answers

    What condition results in the crinkling and crowding of foliage in a rosette pattern?

    <p>Rosetting</p> Signup and view all the answers

    Which symptom is related to the leaf veins showing translucency or a pale while other parts remain normal?

    <p>Vein clearing</p> Signup and view all the answers

    What symptom involves tiny spots, often extremely small, appearing on leaves and other plant parts?

    <p>Flecks</p> Signup and view all the answers

    Which scientist is known for establishing binomial nomenclature of plants?

    <p>Carl von Linne</p> Signup and view all the answers

    What discovery is attributed to Robert Hooke?

    <p>Invention of the compound microscope</p> Signup and view all the answers

    Which phase in the development of plant pathology focused on proving the causes of plant diseases?

    <p>Etiological Phase</p> Signup and view all the answers

    What mixture did Millardet invent in 1885 that contributed to plant disease control?

    <p>Bordeaux mixture</p> Signup and view all the answers

    Who recognized mistletoe as the first plant pathogen?

    <p>Albertus Magnus</p> Signup and view all the answers

    Which of the following describes Theophrastus's belief about plant diseases?

    <p>Diseases resulted from God's wrath</p> Signup and view all the answers

    What was the main focus of the Descriptive Phase in plant pathology?

    <p>Discovery and development of growth methodologies</p> Signup and view all the answers

    Which event is associated with Thoullier in relation to plant diseases?

    <p>Discovery of ergotism and its spread</p> Signup and view all the answers

    What was the significance of Louis Pasteur's work in the context of plant pathology?

    <p>He established the germ theory of disease.</p> Signup and view all the answers

    Which compound was first identified as a dithiocarbamate fungicide in 1934?

    <p>Thiram</p> Signup and view all the answers

    What did Anton deBary prove regarding potato late blight?

    <p>It was caused by a fungus.</p> Signup and view all the answers

    What advancement in fungicide development occurred in 1965?

    <p>The development of the first systemic fungicide.</p> Signup and view all the answers

    What was one of the early observations made by Needham regarding nematodes?

    <p>He first observed nematodes in 1743.</p> Signup and view all the answers

    What did the widespread use of systemic fungicides in the 1970s lead to?

    <p>The appearance of resistant fungal strains.</p> Signup and view all the answers

    Which disease was responsible for significant losses in peach trees during the 1910s?

    <p>Peach root rot.</p> Signup and view all the answers

    What was Charles Darwin's major publication focused on?

    <p>The origin of species by means of natural selection.</p> Signup and view all the answers

    What did Robert Petri contribute to microbiology?

    <p>The creation of artificial nutrient media.</p> Signup and view all the answers

    What was a primary finding of Prevost regarding smut disease?

    <p>Smut spores gave rise to smut disease.</p> Signup and view all the answers

    What discovery did Erwin Smith make regarding a specific bacteria related to plant diseases?

    <p>It caused crown root gall in plants.</p> Signup and view all the answers

    What specific disease caused significant destruction of coffee in Southeast Asia during the late 19th century?

    <p>Coffee rust</p> Signup and view all the answers

    Which enzymatic activity was reported to be involved in soft rot of vegetables?

    <p>Cytolytic enzymes</p> Signup and view all the answers

    What significant role did viruses play in plant disease as demonstrated by deBary's conclusion?

    <p>Produced toxins that kill plant cells.</p> Signup and view all the answers

    Which pathogen is linked to severe losses of rubber tree plantations in South America?

    <p>Armillaria mellea</p> Signup and view all the answers

    Which organism was shown to cause coffee diseases in 1963?

    <p>Protozoans</p> Signup and view all the answers

    Which disease is responsible for the serious loss of American elm trees since 1918?

    <p>Dutch elm disease</p> Signup and view all the answers

    Which technological advancement in the late 1980s focused on plant disease resistance?

    <p>Genetic engineering</p> Signup and view all the answers

    What type of losses do leaf pathogens like M.fijiensis primarily lead to?

    <p>Defoliation and weakening of plants</p> Signup and view all the answers

    What was revealed about the tobacco mosaic virus in 1898 by Beijerinck?

    <p>It was caused by a contagious living fluid.</p> Signup and view all the answers

    Which pathogen has caused continuous heavy losses in cacao, notably in Africa?

    <p>Swollen shoot of cacao</p> Signup and view all the answers

    What was a major consequence of sugar cane mosaic in agricultural production?

    <p>Great losses on sugar cane and corn</p> Signup and view all the answers

    Which pathogen is associated with the white halo around spots of wildfire disease?

    <p>Pseudomonas tabaci</p> Signup and view all the answers

    What did A. Mayer demonstrate regarding plant diseases in 1886?

    <p>Pathogenicity of leaf juices with yellow mosaic.</p> Signup and view all the answers

    Which disease is known to significantly weaken crops and predispose them to attacks by other pathogens?

    <p>Coffee rust</p> Signup and view all the answers

    What was the significant finding about mollicutes in 1926 by E. Kurosawa?

    <p>They resulted in excessive growth in infected rice seedlings.</p> Signup and view all the answers

    Which disease has notably affected the sugar beet crop in Northern Europe and the Western U.S.?

    <p>Sugar beet yellows</p> Signup and view all the answers

    What significant agricultural loss is attributed to banana leaf spot or Sigatoka?

    <p>Great annual losses in banana cultivation</p> Signup and view all the answers

    Which advancement in plant disease understanding occurred during the 1990s?

    <p>Development of systemic acquired resistance.</p> Signup and view all the answers

    What phenomenon is caused by fungal infections such as Fusarium spp. in corn grains?

    <p>Esophageal cancer</p> Signup and view all the answers

    What was the primary belief about plant diseases held by Theophrastus?

    <p>They were manifestations of God's wrath.</p> Signup and view all the answers

    Which significant contribution did Robert Hooke make to plant pathology?

    <p>Invention of the microscope.</p> Signup and view all the answers

    Who is credited with improving the microscope and discovering microorganisms?

    <p>Antonius van Leeuwenhoek</p> Signup and view all the answers

    What phase of plant pathology focuses on proving the causes of plant diseases?

    <p>Etiological Phase</p> Signup and view all the answers

    What was the primary discovery associated with Millardet in the context of controlling plant diseases?

    <p>Invention of the Bordeaux mixture.</p> Signup and view all the answers

    Which holiday celebrated the rust god Robigus in ancient Rome?

    <p>Robigalia</p> Signup and view all the answers

    What significant aspect of plant pathology began its Descriptive Phase?

    <p>Identification of plant pathogens.</p> Signup and view all the answers

    In which year was the concept of binomial nomenclature established?

    <p>1735</p> Signup and view all the answers

    What is Sarcody in plant pathology?

    <p>The abnormal swelling of the bark above an injury</p> Signup and view all the answers

    Which term describes sunken necrotic areas with cracked borders?

    <p>Canker</p> Signup and view all the answers

    What does chlorosis indicate in plant tissues?

    <p>Yellowing not caused by light deficiency</p> Signup and view all the answers

    What type of plant disease symptom is characterized by curled leaves?

    <p>Curling</p> Signup and view all the answers

    What does the term 'blight' refer to in plant pathology?

    <p>Extensive sudden death of host tissues</p> Signup and view all the answers

    What is the term used to describe parasites that can thrive on both living hosts and dead organic matter?

    <p>Facultative parasites</p> Signup and view all the answers

    Which response is characterized by the immediate death of cells surrounding an invading pathogen?

    <p>Hypersensitive response</p> Signup and view all the answers

    What do we call the genetic variability within a pathogen species that affects its ability to infect different hosts?

    <p>Pathogen races</p> Signup and view all the answers

    Which term describes the interaction where there is a specific gene in the host for resistance matched by a gene for avirulence in the pathogen?

    <p>Gene-for-gene relationship</p> Signup and view all the answers

    What type of parasite primarily relies on living organisms for its nutritional needs?

    <p>Biotrophs</p> Signup and view all the answers

    Which type of research differentiates between disease resistance, escape, and endurance?

    <p>Barrus' research</p> Signup and view all the answers

    What does the term 'apoptosis' refer to in the context of plant responses?

    <p>Programmed cell death</p> Signup and view all the answers

    Which of the following correctly describes semi-biotrophs or facultative saprophytes?

    <p>Primarily live as parasites, but can also grow on dead matter</p> Signup and view all the answers

    Which scientist established the concept of host genetic resistance corresponding to pathogen genetic avirulence?

    <p>H.H. Flor</p> Signup and view all the answers

    What was identified by Orton regarding plant diseases?

    <p>Distinction between resistance, escape, and endurance</p> Signup and view all the answers

    What is the primary characteristic of horizontal resistance in plants?

    <p>Weak but effective against all races of a pathogen species.</p> Signup and view all the answers

    Which term best describes the rapid death of cells in response to pathogen attack as proposed by E. Gaümann?

    <p>Hypersensitivity</p> Signup and view all the answers

    What role did phytoalexins play in plant disease resistance starting in the 1960s?

    <p>They act as toxic compounds against pathogens.</p> Signup and view all the answers

    What was the significance of Mills' 1944 research regarding plant disease epidemiology?

    <p>It correlated rain duration with temperature for infection prediction.</p> Signup and view all the answers

    Which of these diseases is linked to the massive eradication of trees in the U.S.?

    <p>Citrus canker</p> Signup and view all the answers

    Which type of resistance is defined by being effective against one or few pathogen races but is considered strong?

    <p>Vertical resistance</p> Signup and view all the answers

    What is a key feature of the resistance strategy associated with hypersensitivity in plants?

    <p>Isolation of the pathogen through cell death</p> Signup and view all the answers

    In which year did Mills create a predictive table for the infection of apple trees?

    <p>1944</p> Signup and view all the answers

    What is indicated by the phrase 'caused eradication of millions of trees' in reference to citrus canker?

    <p>It resulted in significant agricultural losses.</p> Signup and view all the answers

    Which of the following best describes the impact of disease resistance mechanisms on plant health?

    <p>They enable plants to survive various pathogen races.</p> Signup and view all the answers

    What type of symptom is characterized by excessive growth of plant parts or organs?

    <p>Hyperplastic symptoms</p> Signup and view all the answers

    Which disease is known to have caused significant economic losses in the Philippines due to a viroid?

    <p>Cadang-cadang disease</p> Signup and view all the answers

    Which symptom involves premature falling of leaves due to plant disease?

    <p>Abscission</p> Signup and view all the answers

    What are necrotic symptoms primarily associated with in plant diseases?

    <p>Cell or tissue death</p> Signup and view all the answers

    What is the primary cause of hyperplastic symptoms in plants?

    <p>Increase in the number of cells</p> Signup and view all the answers

    What type of pathogen causes severe losses on tomatoes and tobacco worldwide?

    <p>Virus</p> Signup and view all the answers

    Which condition is particularly associated with the excessive swelling of the bark above an injury?

    <p>Gall formation</p> Signup and view all the answers

    Which disease is notably important for small grains on a global scale?

    <p>Barley yellow dwarf</p> Signup and view all the answers

    Which symptom represents an abnormal roughening of fleshy organs?

    <p>Rusetting</p> Signup and view all the answers

    What type of symptom is caused by protoplast and tissue damage in plants?

    <p>Necrotic symptoms</p> Signup and view all the answers

    Which of the following statements about the emergence of resistance in pathogens is true?

    <p>The widespread use of the first systemic fungicides in the 1970s coincided with the appearance of many resistant fungal strains.</p> Signup and view all the answers

    Which discovery was pivotal in demonstrating the relationship between microorganisms and plant diseases?

    <p>The establishment of Koch's postulates.</p> Signup and view all the answers

    Which event marked the initial use of antibiotics against bacteria in agriculture?

    <p>The use of streptomycin in the 1950s.</p> Signup and view all the answers

    What significant conclusion did Louis Pasteur reach in his research related to disease causation?

    <p>Most infectious diseases are caused by pre-existing microorganisms.</p> Signup and view all the answers

    What was a significant finding of Pier Antonio Micheli in 1729?

    <p>He described numerous new fungi and challenged the idea of spontaneous generation.</p> Signup and view all the answers

    Which finding is associated with Anton deBary's research during 1861-1863?

    <p>He confirmed that potato late blight is caused by a fungus.</p> Signup and view all the answers

    What aspect did Robert Petri contribute to the field of microbiology?

    <p>He invented artificial nutrient media using Petri dishes.</p> Signup and view all the answers

    What was the primary focus of Kühn's book published in the 1870s?

    <p>Diseases of cultivated crops, examining their causes and effects.</p> Signup and view all the answers

    Which symptom is associated with hyperplastic conditions in plants?

    <p>Excessive swelling of tissue</p> Signup and view all the answers

    Which of the following plant diseases is known to cause significant economic losses primarily in the Philippines?

    <p>Cadang-cadang disease</p> Signup and view all the answers

    What defines necrotic symptoms in plants?

    <p>Death of cells or tissues</p> Signup and view all the answers

    Which type of symptom is characterized by a significant increase in cell size within plant tissues?

    <p>Hypertrophy</p> Signup and view all the answers

    Which plant disease's impact is primarily associated with the Mediterranean region and has resulted in severe losses?

    <p>Tomato yellow leaf curl</p> Signup and view all the answers

    What hormone was identified as being produced by the agent of fasciation disease in peas?

    <p>Cytokinin</p> Signup and view all the answers

    Which organism was shown to induce crown gall disease by introducing Transforming DNA into plant cells?

    <p>Agrobacterium tumefaciens</p> Signup and view all the answers

    What is the primary characteristic of pathogenicity in plant pathogens?

    <p>Ability to cause disease</p> Signup and view all the answers

    What disease was discovered to be caused by viroids according to the findings of Diener?

    <p>Potato spindle tuber</p> Signup and view all the answers

    In which decade did researchers show that certain microbes produced plant hormones like indoleacetic acid?

    <p>1950s</p> Signup and view all the answers

    What significant development in plant pathology did Vanderplank contribute in the mid-1960s?

    <p>Foundation of epidemiology</p> Signup and view all the answers

    Which disease is associated with the cereal rust fungus Puccinia graminis, as discovered by Eriksson in 1894?

    <p>Cereal rust disease</p> Signup and view all the answers

    What type of parasite develops intimately with a plant and multiplies at its expense?

    <p>Plant parasite</p> Signup and view all the answers

    By which year had several microbial pathogens been shown to produce gibberellins?

    <p>1950</p> Signup and view all the answers

    What is the primary function of the hormone gibberellin identified in 1939?

    <p>Promotion of stem elongation</p> Signup and view all the answers

    What was the cause and impact of the Irish famine in 1845-46?

    <p>Late blight of potato, leading to significant food loss</p> Signup and view all the answers

    Which disease is associated with the production of aflatoxin and is notably carcinogenic?

    <p>Downy mildew of corn</p> Signup and view all the answers

    Which disease led to the destruction of almost all American chestnut trees between 1904 and 1940?

    <p>Chestnut blight</p> Signup and view all the answers

    What was a significant consequence of the great Bengal famine in 1943?

    <p>Triggered by brown spot of rice epidemics</p> Signup and view all the answers

    Which of the following pathogens is linked to a significant reduction in corn quality and produces yellow rice toxins?

    <p>P.philippinensis</p> Signup and view all the answers

    Which pathogen is infrequently found but is poisonous to humans and animals?

    <p>C.purpurea</p> Signup and view all the answers

    What is one of the economic impacts of the Southern corn leaf blight epidemic in the U.S. in 1970?

    <p>Approximately $1 billion lost</p> Signup and view all the answers

    What impact did the epidemics of downy mildew of tobacco have in North America in 1979?

    <p>Massive decline in tobacco yield</p> Signup and view all the answers

    Which toxin is produced by the fungus A.ochraceus and is associated with downy mildew of tobacco?

    <p>Ochratoxin</p> Signup and view all the answers

    What type of climate is primarily affected by late blight of potato?

    <p>Cool, humid climates</p> Signup and view all the answers

    What is the primary characteristic of biotrophs in plant pathology?

    <p>They can only reproduce in living hosts.</p> Signup and view all the answers

    Which classification of parasites are known to grow on both living and dead materials but primarily remain as parasites?

    <p>Semi-biotrophs</p> Signup and view all the answers

    What significant relationship was established by H.H. Flor in 1946?

    <p>The gene-for-gene relationship between host and pathogen.</p> Signup and view all the answers

    What concept did Orton distinguish in his 1909 research?

    <p>The differences between disease escape, endurance, and resistance.</p> Signup and view all the answers

    What paves the way for the genetic variability within a pathogen species as identified by Barrus in 1911?

    <p>Different pathogen races being restricted to specific host varieties.</p> Signup and view all the answers

    Which type of response is characterized by the death of both attacked and adjacent cells in plants?

    <p>Hypersensitive response</p> Signup and view all the answers

    What did Biffen report regarding the inheritance of resistance in wheat varieties in 1905?

    <p>Resistance was inherited in a Mendelian fashion.</p> Signup and view all the answers

    How do facultative parasites operate in relation to living and dead plant materials?

    <p>They switch between parasitic and saprophytic lifestyles.</p> Signup and view all the answers

    What does the term necrotroph refer to in plant pathology?

    <p>Pathogens that feed on dead organic matter for sustenance.</p> Signup and view all the answers

    What significant observation did Z. Klement and colleagues make in 1964?

    <p>The hypersensitive response operates against bacterial plant pathogens.</p> Signup and view all the answers

    Which of the following describes chlorosis in plants?

    <p>Yellowing of leaves not due to light deficiency.</p> Signup and view all the answers

    What is the defining characteristic of die-back in plants?

    <p>Drying backward from the tip of the plant.</p> Signup and view all the answers

    Which term refers to the large, irregular spots on leaves or fruits due to necrotic injury?

    <p>Blotching</p> Signup and view all the answers

    What does the term 'shot-hole' refer to in plant pathology?

    <p>Perforated appearance of leaves with dead areas dropping out.</p> Signup and view all the answers

    Which plant condition is identified as canker?

    <p>A sunken necrotic area with a cracked border.</p> Signup and view all the answers

    What significant role did Rachel Carson's 'Silent Spring' play in the 1960s?

    <p>It raised awareness about environmental pollution from pesticides.</p> Signup and view all the answers

    Which of the following describes antagonistic microbes used in plant disease control?

    <p>They compete with pathogens and inhibit their effects.</p> Signup and view all the answers

    The discovery of suppressive soils in the early 20th century is significant because they:

    <p>Naturally protect against certain plant diseases.</p> Signup and view all the answers

    What was the first pathogen identified to cause diseases in plants?

    <p>Smut spores</p> Signup and view all the answers

    What is cross protection as discovered in the early 1930s?

    <p>Antagonism between different strains of the same virus to provide immunity.</p> Signup and view all the answers

    As of 1963, which significant approach was first controlled in plant disease management?

    <p>Use of antagonists like Pseudomonas gigantea.</p> Signup and view all the answers

    Which of the following pathogens is associated with the early identification of nematodes?

    <p>Root-knot nematode observed by Needham.</p> Signup and view all the answers

    The banning of certain chemical pesticides in the 1960s coincided with what discovery about their dangers?

    <p>They pose a risk to human health and the environment.</p> Signup and view all the answers

    Which disease is responsible for the historical epidemic that contributed to the Irish famine between 1845 and 1846?

    <p>Late blight of potato</p> Signup and view all the answers

    What was the primary impact of the brown spot of rice epidemic during the great Bengal famine of 1943?

    <p>Reduction in quality of produce</p> Signup and view all the answers

    Which toxin produced by A. flavus is known to be carcinogenic?

    <p>Aflatoxin</p> Signup and view all the answers

    What was the economic consequence of the southern corn leaf blight epidemic in 1970?

    <p>$1 billion lost</p> Signup and view all the answers

    Which disease led to the near extinction of American chestnut trees between 1904 and 1940?

    <p>Chestnut blight</p> Signup and view all the answers

    Which disease is known to cause losses in corn amounting to over P170M annually due to its high impact?

    <p>Downy mildew of corn</p> Signup and view all the answers

    Which disease is responsible for serious losses in rubber tree plantations?

    <p>Rubber leaf blight</p> Signup and view all the answers

    What catastrophic effect did coffee rust have in the 1870s and 1880s?

    <p>It destroyed all coffee in southeast Asia.</p> Signup and view all the answers

    Which fungus is linked to the production of ochratoxin, known for its carcinogenic effects?

    <p>A. ochraceus</p> Signup and view all the answers

    Which of the following diseases causes severe losses in many areas due to the predisposition of the host?

    <p>Fusarium scab of wheat</p> Signup and view all the answers

    What are the consequences of the downy mildew of grapes epidemics experienced in Europe during the 1840s and 1850s?

    <p>Losses from contaminated produce</p> Signup and view all the answers

    What health risks are associated with estrogenic factors produced by Fusarium graminearum found in corn?

    <p>Testes atrophy and reproductive issues</p> Signup and view all the answers

    What is a consequence of severe defoliation in plants infected with certain pathogens?

    <p>Vulnerability to other pathogen attacks</p> Signup and view all the answers

    Which disorder has led to millions of deaths among citrus trees, particularly in the Philippines?

    <p>Citrus tristeza</p> Signup and view all the answers

    Which of the following is a consequence of cereal smuts affecting grains worldwide?

    <p>Continuous but lesser losses</p> Signup and view all the answers

    What is the main distinction between vertical resistance and horizontal resistance in plants?

    <p>Vertical resistance is characterized by strong defense but limited effectiveness, while horizontal resistance is weaker but more universal.</p> Signup and view all the answers

    In what way does hypersensitivity contribute to plant resistance against pathogens?

    <p>It involves quick isolation of the pathogen by killing the attacked cells and some nearby cells.</p> Signup and view all the answers

    Which pathogen is known to significantly affect sugar canes and corn, leading to economic losses?

    <p>Sugar cane mosaic</p> Signup and view all the answers

    What is a direct impact of fungal infections like Fusarium on wheat crops?

    <p>Severe losses in high moisture conditions</p> Signup and view all the answers

    What innovative method did Mills develop in 1944 for predicting infections in apple trees?

    <p>A predictive model based on rain duration and temperature conditions.</p> Signup and view all the answers

    Which pathogen has caused great annual losses due to its role in weakening plants and enabling root-rotting pathogens?

    <p>Banana leaf spot</p> Signup and view all the answers

    What role do phytoalexins play in plant disease resistance, as suggested in the 1960s?

    <p>They are antimicrobial compounds produced in response to pathogen attacks.</p> Signup and view all the answers

    Which of the following correctly identifies the geographic impact of citrus canker?

    <p>It caused eradication of millions of trees in Florida and was a major issue in Asia and Brazil.</p> Signup and view all the answers

    What is a major consequence of the dwarf mistletoe infections on forest ecosystems?

    <p>Serious losses leading to ecosystem instability</p> Signup and view all the answers

    Which aspect of plant pathology was advanced by E. Gaümann’s proposal in 1946?

    <p>The understanding of host-pathogen interactions through hypersensitivity.</p> Signup and view all the answers

    What is a primary factor contributing to the economic burden of sugar beet yellows?

    <p>Cost of disease control measures</p> Signup and view all the answers

    What does the term 'plant pathology' encompass?

    <p>The organisms causing diseases and the environmental factors contributing to these diseases.</p> Signup and view all the answers

    In the context of plant disease resistance, which genes are involved in horizontal resistance?

    <p>Many minor resistance genes that offer broader protection.</p> Signup and view all the answers

    What significant consequence did the fire blight of pome fruits have?

    <p>It resulted in significant annual tree deaths across several regions.</p> Signup and view all the answers

    Study Notes

    Plant Pathology:

    • The study of plants & the environment causing diseases.
    • Objective: Prevent/minimize diseases, increase food production, maintain quality.
    • Economic Importance: ~14.1% of crops lost to diseases, estimated $220 Billion annually in losses.

    Plant Disease Causes:

    • Fungi: Numerous examples, including cereal rusts, causing significant worldwide epidemics and losses.
    • Bacteria: Examples include Citrus Canker, fire blight, & soft rot, leading to substantial agricultural losses.
    • Viruses: Mayer (1886) observed tobacco mosaic, Ivanowski (1892) demonstrated bacterial filtration; Beijerinck (1898) coined the ‘contagious living fluid' term.
    • Protozoa: Discovered in latex plants by Lafont (1909) and coffee by Stahel (1931), conclusively proven to cause coffee diseases by Vermeulen (1963).
    • Mollicutes: Doi et al. (1963) established the role of mollicutes.

    Understanding Pathogens:

    • 1886: De Bary theorized fungi produce toxins to kill cells.
    • 1905: L.R. Jones identified cytolytic enzymes in soft rot.
    • 1915: Pectic enzymes were established as significant in disease formation.
    • 1934: Confirmed that the toxin causes the "white halo" in Pseudomonas tabaci wildfire disease.
    • 1947: Helminthosporium (Bipolaris) sp. was found to produce victorin, causing blight in oats.
    • 1960's: Phytoalexins were discovered to play a role in disease resistance.

    Plant Disease Resistance:

    • Vanderplank (1963) introduced two types of resistance:
      • Vertical: Strong but effective against specific pathogen race(s)
      • Horizontal: Weaker but effective against broad pathogen spectrum

    Epidemiology of Plant Diseases:

    • 1944: Mills created a table to predict apple scab infection based on rain duration and temperature.

    Plant Disease Symptoms:

    • Symptoms: Expressions of plant diseases; examples:
      • Blight: Extensive, sudden death of tissues
      • Chlorosis: Yellowing, not due to light
      • Damping off: Rotting of seedlings before or after emergence
      • Wilting: Can be caused by infectious agents or lack of water
      • Mosaic: Variegated patterns with defined borders
      • Shot Hole: Perforated appearance of leaves due to lesions dropping out

    Disease Triangle:

    • Host, Pathogen, Environment: Optimal conditions for disease development are represented by each side of the triangle.
    • Host: The plant species or variety
    • Pathogen: The disease-causing organism
    • Environment: External factors influencing disease development

    Disease Classification:

    • Classified according to: Affected plant organ, symptom, plant type, and causal agent.

    Plant Pathology

    • The study of organisms and environmental factors that cause disease in plants
    • Plant diseases are caused by malfunctioning of host cells and tissues due to pathogens or environmental factors
    • The malfunctioning can result in the development of symptoms

    Common Terms in Plant Pathology

    • Primary vs. Secondary symptoms: Direct results of disease vs. distant results of disease
    • Localized vs. Systemic symptoms: Limited symptoms (e.g., spots) vs. generalized symptoms (e.g., blight)
    • Histological or Morphological symptoms: Internal symptoms vs. external symptoms
    • General classification of symptoms:
      • Plesionecrotic symptoms: Pre-necrotic symptoms (before death) e.g., wilting

    Signs of Plant Diseases

    • Fungal diseases: Mycelia, spores, fruiting bodies
    • Bacterial diseases: Bacterial cells, bacterial ooze
    • Nematode diseases: Eggs, juveniles, adult nematodes
    • Virus diseases: Virus particles, inclusion bodies
    • Viroid diseases: RNA fragments
    • Diseases caused by parasitic flowering plants: Seeds and the plant itself

    Koch's Rules of Proof of Pathogenicity

    • The suspected causal agent should be present in every sample examined.
    • The suspected causal agent must be isolated and purified.
    • Inoculated pure culture must reproduce the specific disease.
    • The same causal agent must be recovered again from the infected host.

    Non-Parasitic Agents of Plant Diseases: Abiotic Diseases

    • Abiotic diseases or injury: Caused by non-living factors
      • Low temperatures
      • Freezing injury (ice crystals form within or in-between plant cells)
      • Injury caused by air pollutants (gases and particulates)

    History and Discoveries

    • Woronin (1878): First observed myxomycetes which cause clubroot disease of cabbage and root and butt rot of pines
    • Burrill (1878): Discovered that bacteria caused the fire blight disease of pear and apple
    • Erwin Smith: Discovered Agrobacterium tumefaciens as the causal agent of crown root gall
    • A. Mayer (1886): Demonstrated the pathogenicity of leaf juices of tobacco with yellow mosaic
    • Ivanowski (1982): Demonstrated via filtration that bacteria was not the primary agent causing tobacco mosaic
    • Beijerinck (1898): Tobacco mosaic was caused by a “contagious living fluid” called virus.
    • Lafont (1909): Discovered protozoa in cells of latex plants
    • Stahel (1931): Discovered that protozoans infect coffee
    • Vermeulen (1963): Proved that protozoans caused disease in coffee
    • Doi et al. and Ward: Recognized the necrotic defense reaction called the “hypersensitive response.”
    • Z. Klement and colleagues (1964): Recognized that the hypersensitive response also operates against bacterial plant pathogens.
    • Biffen (1905): Reports that the resistance of two wheat varieties and their progeny to a rust fungus was inherited in a Mendelian fashion (Inherited Resistance)
    • Orton (1909): Working with Fusarium wilts distinguished among disease resistance, disease escape, and disease endurance (tolerance)
    • Barrus (1911): Shows that there is genetic variability within a pathogen species; i.e., different pathogen races are restricted to certain varieties of a host species
    • Stakman et al. (1914): Established that different races of a pathogen within a pathogen species differ in their ability to attack certain varieties.
    • H.H. Flor (1946): 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).
    • Vanderplank (1963): Suggests two kinds of resistance:
      • Vertical resistance: Controlled by a few "major" resistance genes; strong but effective only against one or few pathogen races
      • Horizontal resistance: Controlled by many 'minor" resistance genes; weaker but effective against all races of a pathogen species.
    • E. Gaümann (1946): 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.
    • 1960s: In some cases, disease resistance is brought about by phytoalexins.
    • Mills (1944): 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.
    • Late 1980s: Use of genetic engineering to induce resistance
    • 1990s: Discovery of systemic acquired (or induced or activated) resistance; Actigard: 1st commercial synthesized plant defense activator

    Bacterial Diseases

    • Citrus canker: Asia, Africa, Brazil, U.S. - Caused eradication of millions of trees in Florida in the 1910s, 1980s, and the 1990s
    • Fire blight of pome fruits: North America, Europe - Kills numerous trees annually

    Key Facts

    • 1905- L.R.Jones reports involvement of cytolytic enzymes in soft rot of vegetables
    • 1915- Pectic enzymes were found to be significant in disease formation.
    • 1934- Confirmation of toxin as cause of white halo around spots of wildfire disease - wildfire disease caused by Pseudomonas tabaci
    • 1947- Helminthosporium (Bipolaris) sp. which blighted oats was shown to produce victorin
    • 1926- E.Kurosawa showed that the excessive growth of rice seedlings infected with the symbiosis - both the plant and the microorganism benefit from the association.

    Plant-Microbe Interactions

    • Biotroph/obligate parasites: Grow and reproduce in nature only in living hosts
    • Nonobligate parasites: Live on either living or dead hosts and on various nutrient media
    • Semi-biotrophs/facultative saprophytes: Non-obligate parasites that live most of their life cycles as parasites, but under certain conditions, may grow saprophytically on dead organic matter.
    • Necrotrophs/saprophytes: Live most of the time and thrive well on dead organic matter
    • Facultative parasites: Necrotrophs that attack living plants and become parasitic

    Common Symptoms

    • Bleeding: Flow of plant sap from wounds
    • Blight: Extensive sudden death of host tissues
    • Blotch: Large, irregular spots on leaves or fruits with necrotic injury of epidermal cells
    • Callus: Overgrowth of tissue formed due to injury
    • Canker: Sunken necrotic area with cracked border
    • Chlorosis: Yellowing but not due to light
    • Curling: Abnormal bending/curling of leaves
    • Damping off: Rotting of seedlings prior to emergence/rotting of stem closest to soil
    • Die-back: Drying backward from the tip
    • Etiolation: Yellowing caused by inadequate light
    • Savoying: The cupping or pocketing of parts of the leaf; underdevelopment of veins of leaf margins.
    • Scab: Slightly raised, rough, ulcer-like lesions
    • Shot-hole: Perforated appearance of a leaf as the dead areas of local lesions drop out
    • Spot: Localized necrotic area also referred to as a lesion
    • Streak or stripe: Long, narrow necrotic lesions on leaves or stems.
    • Rotting: The disintegration and decomposition of host tissue

    History of plant pathology

    • 1913: Organic mercury compounds were developed for seed treatment.
    • 1859: Charles Darwin published "The Origin of Species by Means of Natural Selection".
    • 1928: Alexander Fleming discovered penicillin.
    • 1729: Pier Antonio Micheli described numerous new fungi, challenging the theory of spontaneous generation.
    • 1934: The first dithiocarbamate fungicide, thiram, was introduced.
    • 1743: Needham first observed nematodes.
    • 1965: The first systemic fungicide, carboxin, was developed.
    • 1755: Tillet demonstrated how smut dust infected wheat plants.
    • 1950: Antibiotics, primarily streptomycin, were used against bacteria.
    • 1807: Prevost concluded that smut spores caused smut disease.
    • 1967: Tetracycline antibiotics were used to control mollicutes and fastidious bacteria.
    • 1861-1863: Anton deBary proved that potato late blight was caused by a fungus.
    • Early 1800s: Louis Pasteur established the "germ theory of disease", proving microorganisms came from preexisting ones and caused infectious diseases.
    • Late 1800s: Robert Petri developed artificial nutrient media for cultivating microorganisms.
    • Late 1800s: Robert Koch defined "Koch's postulates" for identifying pathogens.
    • 1870s: Kühn wrote the first book on plant pathology, "Diseases of Cultivated Crops, Their Causes & Their".

    Resistance to Control Measures

    • 1954: A few strains of bacteria were resistant to certain antibiotics.
    • 1963: Strains of fungal plant pathogens were resistant to fungicides.
    • 1970s: Widespread use of systemic fungicides led to the emergence of many resistant fungi.

    Plant Defense Mechanisms

    • 1964: Z. Klement and colleagues discovered that the hypersensitive response operates against bacterial plant pathogens.
    • 1972: A similar necrotic or hypersensitive response, called apoptosis, was described in animals.

    Inheritance of Resistance

    • 1905: Biffen demonstrated the Mendelian inheritance of resistance in wheat varieties against a rust fungus.
    • 1909: Orton distinguished between disease resistance, disease escape, and disease endurance (tolerance).
    • 1911: Barrus showed that there is genetic variability within a pathogen species, leading to different pathogen races that attack specific host varieties.
    • 1914: Stakman et al. demonstrated that different races within a pathogen species differ in their ability to infect specific varieties.
    • 1946: H.H. Flor, studying the rust disease of flax, established the gene-for-gene relationship: for every gene for resistance in the host, there is a corresponding gene for avirulence in the pathogen, and vice versa.

    Examples of Severe Losses Caused by Plant Diseases

    • Cereal rusts: Frequent severe epidemics cause huge annual losses worldwide.
    • Cereal smuts: Continuous, but less severe, losses on all grains worldwide.
    • Ergot of rye and wheat: Infrequent but poisonous to humans and animals.
    • Late blight of potato: Annual epidemics, responsible for the Irish famine (1845-46).
    • Brown spot of rice: Epidemics, including the great Bengal famine (1943).
    • Southern corn leaf blight: Historic epidemic in the US in 1970, causing $1 billion in losses.
    • Powdery mildew of grapes: European epidemics in the 1840s-1850s.
    • Downy mildew of grapes: European epidemics in the 1870s-1880s.
    • Downy mildew of tobacco: European epidemics in the 1950s-1960s and a North American epidemic in 1979.
    • Downy mildew of corn: Losses can be as high as 95% in the Philippines.
    • Chestnut blight: Destroyed nearly all American chestnut trees between 1904 and 1940.

    Types of Crop Losses

    • Reduction in yield: The quantity of produce harvested is significantly lower due to disease.
    • Losses from deterioration during storage, marketing, or transport: The quality of the product is degraded after harvest.
    • Reduction in quality of produce: The product is not aesthetically pleasing or meets quality standards, leading to reduced market value.
    • **Losses from produce contaminated with toxins that cause various disorders:**Toxins produced by the pathogen can cause illness or death.

    Disease Triangle

    • The development of plant diseases is dependent on a balance between the host, the pathogen, and the environment.
    • Each side of the triangle represents the factors that contribute to disease development.
    • The length of each side is determined by the optimal conditions for disease development.
    • If one side of the triangle is weak or unfavorable, the likelihood of disease developing is reduced.

    Symptoms of Plant Diseases

    • Symptoms are the visible effects of a plant disease on the host.
    • Symptoms are expressions of the host's reaction to the pathogen.

    Examples of Plant Disease Symptoms

    • Blight: Sudden, extensive withering and death of leaves, stems, or blossoms.
    • Canker: Localized dead areas on stems, twigs, or branches.
    • Damping-off: Pre-emergence death of seedlings due to stem rot.
    • Dieback: Gradual death of branches and stems from the tips back toward the base.
    • Fasciculation/fasciation: Clustering of roots, flowers, fruits, or twigs around a common point.
    • Flecks: Extremely tiny spots on leaves, stems, or other plant parts.
    • Gumming/gummosis: Oozing of viscous gum from wounds in bark.
    • Leak: Exudation or leakage of juices from soft-rotted portions.
    • Mosaic: Variegated patterns with defined borders, often on leaves.
    • Mottling: The variegation is less defined than mosaic, with diffused color boundaries.
    • Mummification: A shriveled, dried, and often hardened fruit, resulting from fungal infection.
    • Phyllody: Sepals, petals, stamens, or carpels become leaf-like.
    • Pitting: Depressions or pits on the surface of fruits, tubers, and other fleshy organs.
    • Rosetting: Crowding of the foliage in a rosette.
    • Vein clearing: The leaf veins are translucent or pale, while the rest of the leaf is its normal color.
    • Virescence or greening: Development of chlorophyll in tissues where it's normally absent.
    • Wilting: May be due to an infectious agent or lack of water.

    Plant Pathogen Lifecycle

    • Symbiosis: Both the plant and microorganism benefit from the relationship.
    • Biotroph/obligate parasites: Grow and reproduce only in living hosts.
    • Nonobligate parasites: Live on either living or dead hosts and various nutrient media.
    • Semi-biotrophs/facultative saprophytes: Non-obligate parasites that live most of their lives as parasites but may grow saprophytically on dead organic matter under certain conditions.
    • Necrotrophs/saprophytes: Live and thrive on dead organic matter.
    • Facultative parasites: Necrotrophs that attack living plants and become parasitic.

    Economic Importance of Plant Diseases

    • Plant diseases account for 14.1% of crop losses globally.
    • The total annual worldwide crop loss from plant diseases is approximately $220 billion.

    Types of Plant Pathogens

    • Fungal Diseases
      • Root knot: Worldwide, continuous losses on vegetables and other plants.
      • Sugar beet cyst nematode: Northern Europe, Western U.S., continuous severe annual losses on sugar beets.
      • Soybean cyst nematode: Asia, North & South America, continuous serious losses on soybeans.
    • Bacterial Diseases
      • Soft rot of vegetables: Worldwide, huge losses of fleshy vegetables.
    • Phytoplasma Diseases
      • Peach yellows : Eastern U.S., Russia, historical losses, killing millions of peach trees.
      • Pear decline: Pacific coast states & Canada, Europe (1960s), millions of pear trees killed.

    Plant Pathology: A Historical Overview

    • Theophrastus (father of botany) considered plant diseases as divine wrath.
    • Robigus (Roman rust god) had a special holiday, Robigalia.
    • Mistletoe was recognized as the first plant pathogen by Albertus Magnus.
    • Spontaneous generation was an early theory explaining the origin of plant diseases.

    Early Developments in Plant Pathology

    • Descriptive Phase: This focused on identifying plant diseases and developing methods for studying microbes.
    • Experimental Phase: Experiments were designed to answer fundamental questions about plant diseases.
    • Etiological Phase: The main focus was on proving the specific causes of plant diseases.
    • Search for Control: Scientists sought ways to control plant pathogens.

    Biology & Plant Pathology in the Renaissance & the 1800s

    • Thoullier (1670) observed ergotism (“Holy Fire”) spreading through infected wheat.
    • Robert Hooke invented the compound microscope and discovered the cell.
    • Antonius van Leeuwenhoek improved the microscope and discovered microorganisms.
    • Carl von Linne (1735) established binomial nomenclature in his work "Systema Naturae."
    • Charles Darwin (1859) published "The Origin of Species by Means of Natural Selection."
    • Pier Antonio Micheli (1729) described many fungi and contested spontaneous generation.
    • Needham (1743) observed nematodes for the first time.
    • Tillet (1755) demonstrated how smut dust infected wheat.
    • Prevost (1807) concluded that smut spores caused smut disease.
    • Anton deBary (1861-1863) proved that potato late blight was caused by a fungus.
    • Louis Pasteur established the germ theory of disease, proving that microorganisms are derived from pre-existing ones.
    • Robert Petri developed artificial nutrient media for growing microorganisms (Petri dishes).
    • Robert Koch established Koch's postulates, proving the cause of a disease through a set of criteria.
    • Kühn wrote the first book on plant pathology, "Diseases of Cultivated Crops, Their Causes & Their Control," in the 1870s.
    • Woronin (1878) observed myxomycetes causing clubroot disease in cabbage.
    • Burrill (1878) discovered that bacteria caused fire blight in pear and apple trees.
    • Erwin Smith identified Agrobacterium tumefaciens as the cause of crown gall disease.

    Key Developments in 20th Century Plant Pathology

    • Chemical Control

      • Bordeaux Mixture (1885) invented by Millardet.
      • Organic Mercury Compounds (1913) developed for seed treatment.
      • Penicillin (1928) discovered by Alexander Fleming.
      • Thiram (1934) the first dithiocarbamate fungicide.
      • Carboxin (1965) the first systemic fungicide.
      • Streptomycin (1950s) used to combat bacteria.
      • Tetracycline Antibiotics (1967) used against mollicutes and fastidious bacteria.

    • Pathogen Resistance

      • Antibiotic Resistance (1954) - some bacteria developed resistance.
      • Fungicide Resistance (1963) - some fungal pathogens became resistant.
      • Widespread Resistance (1970s) - increased use of systemic fungicides led to several fungi developing resistance.

    • Genetic Engineering

      • Late 1980s: Genetic engineering used to induce resistance in plants.

    • Systemic Acquired Resistance (SAR)

      • 1990s: Research on SAR (also known as induced or activated resistance) gained momentum.
      • Actigard (1990s) became the first commercial synthesized plant defense activator.

    • Understanding Pathogen Mechanisms

      • Toxins (1886) - De Bary concluded that fungi produce toxins to kill cells.
      • Cytolytic Enzymes (1905) - L.R. Jones observed their involvement in soft rot.
      • Pectic Enzymes (1915) - Important role in disease development.
      • Wildfire Disease (1934) - confirmed that toxins caused the white halo around infected spots.
      • Victorin (1947) - a toxin produced by Helminthosporium ( Bipolaris) that caused oat blight.
      • Gibberellins (1926) - E. Kurosawa discovered the role of gibberellins in the excessive growth of rice seedlings infected with Gibberella fujikuroi.
      • Fumonisins (1990s) - toxins produced by Fusarium spp. in corn, linked to esophageal cancer.

    • Disease Predisposition

      • Nematode Injuries (1990s) - nematode damage on roots can facilitate entry for other pathogens.
      • Leaf Pathogens (1990s) - weakened plants by leaf pathogens become susceptible to root-rotting pathogens.
      • Defoliation (1990s) - severely defoliated trees become susceptible to fungal infections like Armillaria mellea.

    Economic Impact of Plant Diseases

    • Increased Production Costs

      • Disease control measures raise costs.

    • Commodity Culling

      • Diseased crops need to be culled, increasing financial losses.

    Disease Triangle

    This concept emphasizes the interaction between three elements for disease development:

    • Host: The plant susceptible to infection
    • Pathogen: The organism causing the disease
    • Environment: Factors like temperature, humidity, and soil conditions that influence disease development

    The length of each side of the triangle represents the optimal conditions for disease development. For example, if the host is resistant or of the wrong age, the "Host Side" of the triangle will be small.

    Key Plant Disease Terms

    • Disease - a significant deviation from the normal physiological functions and processes of a plant.

    • Symptomatology - the study of plant disease symptoms and disease diagnosis.

    • Symptoms - the visible, macroscopic expressions of a plant's reaction to disease.

    • Signs - the visible, macroscopic structures of the pathogen on the host plant.

    • Sclerotia - compact, dormant masses of fungal tissue.

    • Conidia - asexual spores produced by fungi.

    • Sporangia - a structure that produces and releases spores.

    • Zoospores - motile asexual spores.

    • Symptoms of Plant Diseases

      • Blight - a rapid and extensive killing of leaves, flowers, or fruits.
      • Canker - a localized, sunken, dead area on a stem or branch.
      • Damping-off - a disease that kills seedlings before or shortly after germination.
      • Dieback - the gradual death of plant parts starting from the tips.
      • Leaf spots - small, localized areas of dead tissue on leaves.
      • Mildew - a superficial powdery growth on plant surfaces caused by fungi.
      • Rust - a disease caused by rust fungi, characterized by orange, brown, or black pustules on the host.
      • Scab - a rough, scabby or crusty lesion on fruits, tubers, or stems.
      • Smut - a fungal disease that produces black, dusty spores.
      • Wilt - a disease that causes the plant to droop and become limp.
      • Fasciculation - clustering of roots, flowers, fruits, or twigs around a common point.
      • Flecks - extremely tiny spots on leaves.
      • Gumming - the oozing of gummy substance from wounds in bark.
      • Leak - exudation of juices from soft-rotted portions.
      • Mosaic - variegated patterns with defined borders on leaves.
      • Mottling - variegation with less defined boundaries compared to mosaic.
      • Mummification - shriveled, dried fruit or organs.
      • Phyllody - sepals, petals, stamens, or carpels become leaf-like.
      • Pitting - depressions or pits on fruits, tubers, or other fleshy parts.
      • Rosetting - crowding of leaves, forming a rosette shape.
      • Vein clearing - translucent or pale leaf veins with the rest of the leaf in its normal color.
      • Virescence - chlorophyll development in tissues or organs where it is normally absent.
      • Wilting - may be caused by an infectious agent or lack of water.

    Plant Pathology

    • Is the study of plant diseases
    • The term comes from the Greek words "pathos" (suffering) and "logos" (study)

    History of Plant Pathology

    • Theophrastus was a Greek philosopher who is considered the "father of botany"
    • Theophrastus believed that plant diseases were the result of God's wrath
    • The Roman god Robigus was associated with rust diseases
    • The Romans held a special holiday, the Robigalia, to appease Robigus
    • Albertus Magnus recognized mistletoe as the first plant pathogen
    • Early ideas about the generation of plant diseases focused on spontaneous generation

    Plant Pathology in the Early Renaissance and 1800s

    • Thoullier observed that ergotism, also known as Holy Fire, spread through consuming infected wheat in 1670
    • Robert Hooke invented the compound microscope and discovered the "cell"
    • Antoni van Leeuwenhoek improved the microscope and discovered microorganisms
    • Carl von Linne established binomial nomenclature for plants and published "Systema Naturae" in 1735
    • Ward recognized the hypersensitive response – a necrotic defense reaction in plants

    The Main Areas of Progress in Plant Pathology

    • Chemical Control of Plant Diseases:
      • Millardet in 1885 invented Bordeaux mixture, a fungicide.
    • Biotroph/obligate parasites grow and reproduce only in living hosts
    • Non-obligate parasites can grow and reproduce on living or dead hosts and different nutrient media
    • Semi-biotrophs/facultative saprophytes live as parasites but can grow on dead organic matter under certain conditions.
    • Necrotrophs/saprophytes thrive on dead organic matter
    • Facultative parasites are nectrotrophs that can attack living plants
    • Hypersensitive Response:
      • E. Gaümann proposed that plant resistance in many cases is due to hypersensitivity. Infected cells die immediately, isolating the pathogen.
      • Z. Klement and colleagues discovered that the hypersensitive response also works against bacterial plant pathogens
    • Inherited Resistance:
      • Biffen in 1905 discovered that the resistance of wheat varieties to a rust fungus was inherited following Mendel's laws.
    • Disease Escape & Disease Endurance:
      • Orton in 1909 differentiated among disease resistance, disease escape, and disease endurance (tolerance).
    • Racial Specialization:
      • Barrus in 1911 demonstrated that there is genetic variability within a pathogen species, with different pathogen races being restricted to certain host varieties.
    • Gene-for-Gene Relationship:
      • Stakman and colleagues in 1914 established that races of a pathogen within the same species differ in their ability to attack certain varieties.
      • H.H. Flor in 1946 discovered that for each host resistance gene, there is a corresponding avirulence gene in the pathogen, and vice versa.
    • Vertical & Horizontal Resistance:
      • Vanderplank in 1963 suggested two types of resistance:
        • Vertical resistance: controlled by Major resistance genes; strong but effective only against one or few pathogen races.
        • Horizontal resistance: controlled by many minor resistance genes; weaker but effective against all races of a pathogen species.

    Epidemiology of Plant Disease

    • Mills in 1944 developed a table to predict apple scab infection based on the duration of rain and temperature.
    • This information allowed for predicting potential infection.

    Common Plant Diseases

    • Bacterial Diseases:
      • Citrus canker: affects citrus trees, causing eradication of millions of trees in Florida in the 1910s, 1980s, and 1990s
      • Fire blight of pome fruit: affects apple and pear trees, causing significant losses every year
      • Plum pox: a spreading epidemic affecting plums, peaches, and apricots, causing major economic losses due to processing time and techniques
    • Viral Diseases:
      • Barley yellow dwarf: widespread and significant on small grains
      • Tomato yellow leaf curl: impacting tomato, bean, and other plants in many regions
      • Tomato spotted wilt virus: affecting tomato, tobacco, peanuts, and ornamentals
      • Cadang-cadang disease: affecting coconut palms in the Philippines, causing significant economic losses.
    • Viroid Diseases:
      • Cadang-cadang disease: a viroid disease that has caused over $200 million in losses in the Philippines

    Plant Disease Symptoms

    • Necrotic symptoms: protoplast, cell, or tissue death leading to blight, scorch, or canker
    • Hypoplastic symptoms: failure of tissue differentiation or development, leading to stunting or chlorosis
    • Hyperplastic symptoms: overdevelopment of plant parts or organs, leading to gall formation:
      • Hypertrophy: Overdevelopment of cells due to an increase in size
      • Hyperplasia: Abnormal increase in the number of cells
    • Abscission: premature falling of leaves
    • Blast: sudden death of young buds, inflorescence, or young fruits
    • Bleeding: flow of plant sap from wounds
    • Blight: extensive, sudden death of host tissues
    • Blotch: irregular spots on leaves or fruits with necrotic injury of epidermal cells
    • Callus: overgrowth of tissue formed due to injury
    • Canker: sunken necrotic area with a cracked border
    • Chlorosis: yellowing not caused by lack of light
    • Curling: abnormal bending or curling of leaves
    • Damping off: rotting of seedlings before emergence or rotting of the stem near the soil surface
    • Die-back: drying backward from the tip
    • Etiolation: yellowing caused by inadequate light
    • Rusetting: a superficial brownish roughening of fleshy organs due to suberization of epidermal or subepidermal tissues
    • Sarcody: abnormal swelling of bark above wounds due to the accumulation of food materials
    • Savoying: cupping or pocketing of parts of the leaf; underdevelopment of leaf veins or margins
    • Scab: slightly raised, rough, ulcer-like lesions
    • Shot-hole: perforated appearance of a leaf as dead areas of local lesions drop out.
    • Spot: a localized necrotic area (also referred to as a lesion)
    • Streak or stripe: long, narrow necrotic lesions on leaves or stems

    Historical Development of Plant Pathology

    • 1913 - The development of organic mercury compounds for seed treatment
    • 1859 - Charles Darwin published "The Origin of Species by Means of Natural Selection"
    • 1729 - Pier Antonio Micheli described numerous fungi and challenged the theory of spontaneous generation
    • 1743 - Needham was the first to observe nematodes
    • 1755 - Tillet demonstrated how smut dust infected wheat plants.
    • 1807 - Prevost concluded that smut spores caused the disease
    • 1861-63 - Anton de Bary proved that potato late blight was caused by a fungus
    • 1822 - Louis Pasteur proved that microorganisms originated from preexisting ones and that most infectious diseases were caused by germs, establishing the "germ theory of disease".
    • Late 19th Century - Robert Koch, established "Koch's postulates" which are criteria used to determine whether a specific microorganism causes a specific disease.
    • 1870s - Kühn wrote the first book on plant pathology, “Diseases of Cultivated Crops, Their Causes & Their Control”.
    • 1880s-1890s - Robert Petri, a German bacteriologist, developed agar plates and Petri dishes for culturing microorganisms.
    • 1928 - Alexander Fleming discovered penicillin, the first antibiotic from a fungus.
    • 1934 - The first dithiocarbamate fungicide (thiram) was developed.
    • 1950 - Antibiotics, primarily streptomycin, were utilized against bacteria
    • 1965 - Carboxin, the first systemic fungicide, was developed.
    • 1967 - Tetracycline antibiotics were found to control mollicutes and fastidious bacteria
    • 1939 - Gibberellin, a plant growth regulator produced by the fungus Gibberella, was identified.

    Resistance to Bactericides & Fungicides

    • 1954 - A small number of bacteria were observed to be resistant to certain antibiotics
    • 1963 - Fungi were found to be resistant to fungicides
    • 1970s - Widespread use of systemic fungicides resulted in a significant emergence of resistant fungi
    • 1967 - Mollicutes were observed in Japan
    • 1971 - T. O Diener discovered viroids as the cause of potato spindle tuber disease
    • 1950s - It was shown that numerous plant pathogenic fungi and bacteria produced indoleacetic acid (IAA), a plant hormone.
    • Mid 1960s - The agent causing leafy gall disease of peas was shown to produce cytokinin, whose symptoms could be reproduced by treating plants with kinetin, a cytokinin derived from animals.
    • 1970s and 1980s - Agrobacterium tumefaciens, a common soil bacteria, was shown to induce crown gall disease in plants through the introduction of transforming DNA into plant cells, leading to an unregulated production of cytokinin and IAA, resulting in tumors.

    Epidemiology & Pathogenicity

    • 1963 - Vanderplank published "Plant Diseases: Epidemics and Control" and established epidemiology as a key field in plant pathology.
    • Parasite - An organism that lives on or in another organism and obtains its food from the host.
    • Parasitism - The removal of food by a parasite from it's host.
    • Plant parasite - An organism that becomes intimately associated with a plant and multiplies or grows at the expense of the plant
    • Pathogenicity - The ability of a pathogen to cause disease.
    • Symbiosis - A relationship beneficial to both the plant and the microorganism
    • Biotroph/obligate parasite - Thrive in living hosts
    • Nonobligate parasite - Can live on living or dead hosts
    • Semi-biotrophs/facultative saprophytes - Non-obligate parasites that primarily live as parasites but can grow saprophytically on dead organic matter
    • Necrotrophs/saprophytes - Thrive on dead organic matter
    • Facultative parasites - Necrotrophs that attack living plants

    Genetic Inheritance of Resistance & Pathogenicity

    • 1894 - Eriksson demonstrated that the cereal rust fungus Puccinia graminis has different biological races that are morphologically similar but differ in pathogenicity to certain host plants.
    • 1902 - H.M. Ward identified the necrotic defense reaction known as the "hypersensitive response".
    • 1964 - Z. Klement and colleagues observed that the hypersensitive response works against bacterial plant pathogens
    • 1972 - A similar necrotic or hypersensitive response was observed in animals called apoptosis
    • 1905 - Biffen confirmed that the resistance of two wheat varieties, and their progeny, to a rust fungus was inherited in a Mendelian fashion (Inherited Resistance)
    • 1909 - Orton working with the Fusarium wilts of plants, noted the distinctions among disease resistance, disease escape, and disease endurance (tolerance).
    • 1911 - Barrus demonstrated genetic variability within a pathogen species, showing that different pathogen races are restricted to specific varieties of a host species.
    • 1914 - Stakman et al. determined that different races of a pathogen within the same species differ in their ability to attack varying varieties of a host
    • 1946 - H.H. Flor, while investigating the rust disease of flax, established that for each gene for resistance in the host, there was a corresponding gene for avirulence in the pathogen.

    Important Plant Diseases

    • **Cereal smuts (e.g. Ustilago) ** - Worldwide, constant, although less than previously, losses in all grains
    • Ergot of rye and wheat (Claviceps purpurea) - Worldwide, infrequent but poisonous to humans and animals.
    • Late blight of potato (Phytophthora infestans) - Found in cool, humid climates, causes annual epidemics such as the Irish famine (1845-46)
    • Brown spot of rice (Helminthosporium oryzae) - Found in Asia, causes epidemics such as the great Bengal famine (1943)
    • Southern corn leaf blight (Bipolaris maydis) - Significant in the US, caused an epidemic in 1970, costing $1 billion in losses
    • Powdery mildew of grapes (Uncinula necator) - Worldwide; European epidemics (1840s–1850s)
    • Downy mildew of grapes (Plasmopara viticola) - US and Europe ; European epidemic (1870s–1880s)
    • Downy mildew of tobacco (Peronospora tabacina) - US and Europe ; European epidemic (1950s–1960s) and epidemic in North America (1979)
    • Downy mildew of corn (Peronosclerospora philippinensis) - Philippines; Potential losses as high as 95%, amounting to over P170M annually
    • Chestnut blight (Cryphonectria parasitica) - US, destroyed nearly all American chestnut trees (1904–1940)
    • Plum pox or sharka (Plum pox virus) - Europe, North America; Spreading severe epidemic on plums, peaches, apricots
    • Barley yellow dwarf(Barley yellow dwarf virus) - Worldwide, significant in small grains
    • Tomato yellow leaf curl(Tomato yellow leaf curl virus) - Mediterranean countries, Caribbean Basin, US; severe losses of tomatoes, beans, etc.
    • Tomato spotted wilt virus (Tomato spotted wilt virus) - Worldwide, infects tomato, tobacco, peanuts, ornamentals, etc.
    • Cadang-cadang disease (Coconut cadang-cadang viroid) - Philippines, first observed in 1918; losses of over $200M (caused by a viroid)

    Concepts of Plant Disease

    • Plant disease can be defined in several ways.
    • Whetzel (1929) described plant disease as a "physiological malfunctioning due to animate agents"
    • Stakman & Harrar (1957) defined it as a "deviation from normal growth or structure"
    • Horsfall and Dimond viewed it as a "malfunctioning process caused by continuous irritation"
    • Merril (1980) described it as an "interaction between an organism and its environment which results in abnormal changes in the organism"

    Symptoms of Plant Disease

    • Plant diseases progress over time while injury is an instantaneous event.
    • Abscission - Premature falling of leaves
    • Blast - Sudden death of young buds, inflorescence or young fruits
    • Blight - Necrotic lesions or discolored areas
    • Canker - Necrotic lesions that can be sunken or raised
    • Chlorosis - yellowing or loss of chlorophyll
    • Damping-off - Rotting of seedlings at or near soil-level
    • Dieback - Progressive death of twigs, branches, or roots
    • Galls - Abnormal growths or swellings
    • Leaf spot - Small, localized necrotic spots on leaves
    • Mildew - Powdery or downy growth on plant surfaces
    • Mosaic - Discolored patches on leaves
    • Necrosis - Death of cells or tissues
    • Rot - Soft and watery breakdown of tissues
    • Rust - Orange, brown, or black pustules on plant surfaces
    • Scab - Rough, crustlike lesions on plant surfaces
    • Scorch - Necrotic browning of leaf margins
    • Stunting - Reduced growth and development
    • Wilt - drooping and wilting due to loss of water

    Plant Pathology

    • Study of the organisms and environmental factors that cause disease in plants

    Plant Disease History

    • 1807 - Prevost concluded that smut spores caused wheat smut
    • 1861-1863 - Anton deBary proved that potato leaf blight was caused by phytophtora infestans
    • 1960s - Banning of mercury pesticides, DDT, and chlorinated hydrocarbons

    Control Methods & Resistance

    • Early 20th century - Discovery of suppressive soils, antagonistic microbes, and cross protection
    • 1963 – First controlled use of antagonists; P. gigantea against H.
    • 1963 – Vanderplank suggested two kinds of resistance:
      • Vertical Resistance: Strong resistance controlled by a few genes, effective against one or a few pathogen races
      • Horizontal Resistance: Weaker resistance controlled by many genes, effective against all races of a pathogen species
    • 1946 - E. Gäumann proposed that plants remain resistant through hypersensitivity, leading to localized cell death and pathogen isolation
    • 1960s - Disease resistance is sometimes brought about by phytoalexins, compounds produced by plants in response to pathogen attack

    Epidemiology of Plant Disease

    • Mills developed a table to predict apple scab infection based on temperature and rainfall duration
    • This information can be used to predict and control the disease

    Disease Examples

    • Citrus Canker: Causes eradication of millions of citrus trees, widespread in various regions
    • Fire Blight of Pome Fruits: Kills numerous trees annually, found in North America and Europe
    • Cereal Smuts: Continuous losses on all grains, worldwide occurrence
    • Late Blight of Potato: Annual epidemics, caused the Irish Famine of 1845-1846
    • Brown Spot of Rice: Epidemics, including the Bengal Famine of 1943
    • Southern Corn Leaf Blight: Significant historical impact, epidemic in 1970 resulted in $1 billion in losses
    • Powdery Mildew of Grapes: European epidemics in the 1840s-1850s
    • Downy Mildew of Grapes: European epidemic in the 1870s-1880s
    • Downy Mildew of Tobacco: European epidemic in the 1950s-1960s, North American epidemic in 1970
    • Downy Mildew of Corn: Philippines, loss can be as high as 95%
    • Chestnut Blight: Destroyed almost all American chestnut trees from 1904-1940
    • Dutch Elm Disease: Destroying American elm trees since 1918
    • Pine Stem Rusts: Severe losses in many areas
    • Dwarf Mistletoes: Serious losses in many areas
    • Coffee Rust: Destroyed all coffee in Southeast Asia in the 1870s-1880s
    • Banana Leaf Spot (Sigatoka): Great annual losses
    • Rubber Leaf Blight: Destroys rubber tree plantations
    • Fusarium Scab of Wheat: Severe losses in wet years
    • Sugar Cane Mosaic: Great losses on sugar cane and corn
    • Sugar Beet Yellows: Great losses every year
    • Citrus Tristeza: Millions of trees being killed
    • Swollen Shoot of Cacao: Continuous heavy losses

    Mycotoxin and Food Losses

    • Aflatoxin: Produced by A. flavus in corn and sorghum, carcinogenic
    • Ochratoxin: Produced by A. ochraceaus, causes liver caner
    • Yellow Rice Toxins: Formed by Penicillium spp., caused several deaths in Japan
    • Estrogenic Factor in Corn: Produced by Fusarium graminearum, causes reproductive problems in pigs
    • Fumonisins: Formed by Fusarium spp. in corn grains, causes esophageal cancer

    Plant Disease Symptoms

    • Blight: Extensive, sudden death of host tissues
    • Canker: Sunken, necrotic area with cracked borders
    • Chlorosis: Yellowing of leaves due to lack of chlorophyll
    • Curling: Abnormal bending or curling of leaves
    • Damping Off: Rotting of seedlings before emergence or rotting of stems near the soil
    • Die-Back: Drying backwards from the tip of a plant
    • Etiolation: Yellowing of leaves due to inadequate light
    • Lesion: Localized necrotic area or spot
    • Shot-Hole: Perforated look of a leaf due to the loss of dead areas
    • Streak: Long, narrow necrotic lesions

    Losses Due to Plant Diseases

    • Food Loss
    • Reduction in Quality of Produce
    • Deterioration during storage, marketing or transport
    • Increased cost of production & handling
    • Cost of disease control
    • Cost of culling disease commodities

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    This quiz explores the fundamentals of plant pathology, focusing on the relationships between plants and pathogens. Gain insights into the causes of plant diseases, including fungi, bacteria, viruses, and protozoa, as well as their economic impact on agriculture. Test your knowledge about historical discoveries and the significance of preventing plant diseases.

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