Notes on Important Plant Pathogenic Organisms

Notes on Important Plant Pathogenic Organisms

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Source: TNAU Notes

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Plant Pathogenic Organisms:

Parasites:

• Include both biotic and mesobiotic agents.
• Diseases incited by parasites under suitable environment.
• Association of definite pathogen is essential with each disease.

Biotic Agents:

• Also known as animate causes.
• Living organisms.
• Include Prokaryotes and Eukaryotes.

Prokaryotes:

• True bacteria or bacteria: Facultative parasites, e.g., Citrus canker.
• Rickettsia-like bacteria (RLB): e.g., Citrus greening, Pierce's disease of grape.
• Mollicutes or wall-less prokaryotes.
• Mycoplasma-like organism (MLO): e.g., Sesame phyllody, eggplant little leaf.
• Spiroplasma: e.g., Corn stunt, Citrus stubborn.

Eukaryotes:

• Protists: Unicellular, coenocytic, or multicellular, little/no cell differentiation.
• Fungi: e.g., wilt of cotton.
• Protozoa: e.g., heart rot of coconut.
• Algae: e.g., red rust of mango.
• Parasitic flowering plants (phanerogamic parasites): e.g., Broomrape of tobacco.
• Animals: Extensive cell differentiation, e.g., Nematodes - Root knot nematode.

Mesobiotic Agents:

• Include viruses and viroids.
• Infectious agents; can be crystallized.
• Considered non-living but multiply in living plants.
• Viruses: e.g., yellow mosaic of blackgram.
• Viroids: e.g., spindle tuber of potato.

Non-parasites or Abiotic Agents:

• Also known as non-infectious or physiological disorders.
• Caused by non-living or environmental factors.
• Occur due to disturbances in plant system by improper environmental conditions.

Examples of Abiotic Agents:

• Too low or too high temperature.
• Lack or excess of soil moisture.
• Lack or excess of light.
• Lack of oxygen.
• Air pollution (Toxic gases, etc.).
• Mineral deficiencies or toxicities.
• Soil acidity or alkalinity.
• Toxicity of pesticides.
• Improper agricultural practices.

Important Plant Pathogenic Organisms:

Parasites:

• Parasites are both biotic and mesobiotic agents.
• Diseases are incited by parasites under suitable environments.
• Each disease requires a definite pathogen association.

Biotic Agents:

• Also known as animate causes.
• These are living organisms.

Prokaryotes:

• True bacteria or bacteria: Examples include Citrus canker.
• Rickettsia-like bacteria (RLB): Examples include Citrus greening, Pierce's disease of grape.
• Mollicutes or wall-less prokaryotes.
• Mycoplasma-like organism (MLO): Examples include Sesame phyllody, eggplant little leaf.
• Spiroplasma: Examples include Corn stunt, Citrus stubborn.

Eukaryotes:

• Protists: These are unicellular, coenocytic, or multicellular with little or no cell differentiation.
• Fungi: An example is the wilt of cotton.
• Protozoa: An example is heart rot of coconut.
• Algae: An example is red rust of mango.
• Parasitic flowering plants (phanerogamic parasites): An example is Broomrape of tobacco.
• Animals: These have extensive cell differentiation, e.g., Nematodes - Root knot nematode.

Mesobiotic Agents:

• Include viruses and viroids.
• Infectious agents that can be crystallized.
• Multiply in living plants but considered non-living.
• Viruses: An example is yellow mosaic of blackgram.
• Viroids: An example is spindle tuber of potato.

Non-parasites or Abiotic Agents:

• Also known as non-infectious or physiological disorders.
• Caused by environmental factors when no pathogen is found.
• Result from disturbances in the plant system due to improper environmental conditions.

Examples of Abiotic Agents:

• Extreme temperatures (too low or high).
• Imbalanced soil moisture (lack or excess).
• Inadequate or excessive light.
• Oxygen deficiency.
• Air pollution including toxic gases.
• Mineral imbalances (deficiencies or toxicities).
• Soil pH extremes (acidity or alkalinity).
• Pesticide toxicity.
• Improper agricultural practices.

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Notes on Introduction and History of Plant Pathology

Notes on Introduction and History of Plant Pathology

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Source: eagri.org

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Plant Pathology:

• Plant pathology or phytopathology deals with plant diseases.
• It is concerned with health and productivity of growing plants.
• Phytopathology is a branch of agricultural, botanical, or biological science.
• It deals with causes, resulting losses, and management methods of plant diseases.
• Plant pathology studies nature, cause, and prevention of plant diseases.
• It relates to sciences like biology, physics, chemistry, and more.
• Major objectives include studying biotic, mesobiotic, and abiotic causes of diseases.
• It involves studying disease development and plant-pathogen interaction.
• Development of plant disease management methods is a key objective.

Plant Diseases:

• Plant diseases are recognized by symptoms or sick appearance of plants.
• Plant disease signifies the condition due to disease or its cause.
• Disease is a malfunctioning process caused by continuous irritation.
• Definitions by American Phytopathological Society and British Mycological Society.
• Disease alters physiological processes and energy utilization in plants.
• Disease is a disturbance caused by living entities, non-living agents, or environmental factors.
• Diseases affect food manufacture, translocation, or utilization in plants.

History of Plant Pathology:

• Awareness of plant diseases dates back to antiquity.
• Blasting and mildew mentioned in the Old Testament.
• Ancient religious literature, including Rigveda and Atharvanaveda, mentions plant diseases.
• Sushrute Samhita, Vishnu Puran, Agnipuran, and Vishnudharmottar also discuss plant diseases.
• Vedic period acknowledged diseases caused by microbes.
• "Vraksha Ayurveda" by Surapal, an ancient Indian book on plant diseases.
• Surapal divided plant diseases into internal and external groups.
• Bible mentions diseases like rust, smut, downy mildew, powdery mildew, and blight.
• Theophrastus (370-286 B.C.) studied diseases of trees, cereals, and legumes.
• His book 'Enquiry into plants' recorded observations, not based on experiments.
• Theophrastus noted diseases of different plant groups are autonomous or spontaneous.

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Mycology:

• 1675: Anton von Leeuwenhoek developed the first microscope.
• 1729: P. A. Micheli, Italian botanist, proposed fungi come from spores; father of Mycology.
• 1755: French botanist Tillet published a paper on bunt of wheat; discovered bunt is a wheat disease.
• 1807: I. B. Prevost showed bunt of wheat is a fungus and linked microorganisms to disease.

Key Contributions in Mycology:

• 1821: E. M. Fries published Systema Mycologicum; named as Linnaeus of Mycology.
• 1821: Robertson stated sulphur is effective against peach mildew.
• 1845: Irish Potato famine caused by Phytophthora infestans.
• 1858: J. G. Kuhn published first Plant Pathology textbook.
• 1861: Anton de Bary worked on potato late blight; proved fungi cause diseases; Father of Modern Plant Pathology.
• 1865: Anton de Bary reported heteroecious nature of wheat stem rust.
• 1869: England's coffee production lost to coffee rust; shift to tea cultivation.
• 1874: Robert Hartig published “Important Diseases of Forest Trees.”
• 1875-1912: Brefeld discovered artificial culture methods; studied cereal smut fungi.
• 1877: M. S. Woronin named Club root of Cabbage pathogen as Plasmodiophora brassicae.
• 1878: M. S. Woronin studied life cycle of potato wart disease.
• 1878: Downy mildew of grapevine introduced into Europe; impacted wine industry.
• 1881: H.M. Ward worked on coffee leaf rust; Father of Tropical Plant Pathology.
• 1882: Robert Hartig published "Diseases of Trees"; Father of Forest Pathology.
• 1885: Pierre Millardet discovered Bordeaux mixture for grapevine mildew.
• 1885: A. B. Frank defined and named mycorrhizal associations.
• 1887: Burgundy mixture introduced by Mason.
• 1894: Eriksson described physiologic races in cereal rust fungus.

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PLANT PATHOLOGY (SYLLABUS FOR ICAR’S JRF/SRF(PGS) )

SYLLABUS FOR THE ALL INDIA COMPETITIVE EXAMINATION FOR ADMISSION TO DOCTORAL DEGREE PROGRAMMES AND THE AWARD OF

JRF/SRF (PGS)


04 PLANT PATHOLOGY

Unit 1: History and Principles of Plant PathologyMilestones in phytopathology with particular reference to India. Major epidemics and their social impacts. Historical developments of chemicals, legislative, cultural and biological protection measures including classification of plant diseases. Physiologic specialization, Koch’s postulates. Growth, reproduction, survival and dispersal of plant pathogens. Factors influencing infection, colonization and development of symptoms. Unit 2: Laboratory and Analytical TechniquesPreparation and sterilization of common media. Methods of isolation of pathogens and their identification. Preservation of microorganisms in pure culture. Methods of inoculation. Measurement of plant disease.Detection and Diagnosis of pathogens in seeds and other planting materials: Nucleic acid probes, Southern, Northern and Western hybridization, ELISA, ISEM and PCR. Nucleic acid probes, Southern, Northern and Western hybridization, ELISA, ISEM and PCR. Laboratory equipment and their use: autoclave, hot air oven, laminar flow, spectrophotometer, electrophoresis, light and electron microscopy, incubator, ultracentrifuge, ELISA Reader, Freeze dryer, Nano drop, GC-MS, HPLC, Thermocycler. Unit 3: Physiological and Molecular Plant PathologyAltered metabolism of plants under biotic and abiotic stresses. Molecular mechanisms of pathogenesis: elicitors, recognition phenomenon, penetration, invasion, primary disease determinant. Enzymes and toxins in relation to plant disease. Mechanisms of resistance, Structural and Biochemical defense mechanisms. R-Genes, Phytoanticipins. Phytoalexins. PR proteins, Hydroxyproline rich glycoproteins (HRGP). Antiviral proteins. SAR and ISR. HR and active oxygen radicals. Elementary genetic engineering. Management of pathogens through satellite, antisense - RNA. Ribozymes, coat protein, RNA interference, plantibodies, hypovirulence, cross protection. Useful genes and promoters, plant transformation techniques, biosafety and bioethics. Unit 4: MycologyClassification of fungi (According to the Classification – Kirk et al., 2008). Life cycles of important phytopathogenic fungi. Economic mycology, edible fungi and entomogenous fungi. Mycorrhizal associations. Cell organelles, their morphology, functions and chemical composition. Unit 5: Plant BacteriologyIdentification and classification of bacteria. morphology, ultrastructure and chemical composition of prokaryotic cell in relation to function. Growth curve, nutrition and auxotrophic mutants. Resting cells in elementary bacterial genetics and variability: transformation, conjugation, transduction. Biology of extra chromosomal elements: plasmid borne genes and their expression. Bacteriophages: lytic and lysogenic cycles. Prokaryotic inhibitors and their mode of action. Economic uses of prokaryotes. Morphology, biochemical characteristics, reproduction and life cycle of phytoplasma and other fastidious prokaryotes. Unit 6: Plant VirologyNature, composition and architecture of viruses and viroids. Properties of viruses. Nomenclature and classification of viruses. Variability in viruses. Satellite viruses and satellite RNA. Mycoviruses and baculoviruses. Assay of plant viruses including biological, physical, chemical, serological and molecular methods. Conventional and biotechnological techniques used in detection and diagnosis. Behaviour of viruses in plants including infection, replication and movement. Histopathological changes induced by viruses in plants, inclusion bodies. Transmission of viruses: virus - vector relationships. Unit 7: Plant Disease EpidemiologyConcepts in epidemiology. Development of disease in plant population. Monocyclic and polycyclic pathogens. Role of environment and meteorological factors in the development of plant disease epidemics. Survey, surveillance (including through remote sensing), and prediction and forecasting of diseases. Epidemic analysis and prediction models. Crop loss assessment: critical and multiple point models. Decision support system, cloud computing, GPS, GIS and GS in plant disease epidemiology. Unit 8: Phanerogamic Parasites and Non-parasitic DiseasesDiseases caused by Phanerogamic parasites and their management. Diseases due to unfavourable soil environment, drought and flooding stress etc. Nutritional deficiencies. Primary /secondary air pollutants and acid rain. Unit 9: Fungal Diseases of Crop PlantsFungal diseases of cereals, millets, oilseeds, pulses, fruits, vegetables, plantation, fiber, spices, medicinal and ornamental crops with special reference to etiology, disease cycle, perpetuation, epidemiology and management. Postharvest diseases in transit and storage; aflatoxins and other mycotoxins and their integrated management. Unit 10: Bacterial and Viral Diseases of Crop PlantCrop diseases of cereals, pulses, oilseeds, sugar crops, vegetables, fruits, plantation and fiber crops caused by bacteria, viruses, viroids, phytoplasmas and other fastidious prokaryotes. Mode of transmission and pathogen vector relationships. Epidemiology and management. Unit 11: Management of Plant diseasesGeneral principles of plant quarantine. Exotic pathogens and pathogens introduced into India. Sanitary and phytosanitary issues under WTO, TRIPS and PRA. Genetic basis of disease resistance and pathogenicity: gene for gene hyphothesis;; breeding for disease resistance. Production of disease free seeds and planting materials. Seed certification. Chemical nature and classification of fungicides and antibiotics: their bioassay and compatibility with other agricultural chemicals; resistance to fungicides/ antibiotics; effect on environment. Spraying and dusting equipments, their care and maintenances. Important cultural practices and their role in disease management, solarization, integrated disease management. Microorganisms antagonistic to plant pathogens in soil, rhizosphere and phyllosphere and their use in the control of plant diseases; soil fungistasis. Plant growth promoting Rhizobacteria. Biotechnology for crop disease management.