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Basic of Phytopathology 2 BASIC OF PHYTOPATHOLOGY 2. LECTURE CAUSES AND AGENTS OF PLANT DISEASES AND DISORDERS © 2012 A. Lebeda, B. Mieslerová, M. Sedlářová CAUSES AND AGENTS OF PLANT DISEASES AND DISORDERS I. Abionosis -Non-infectious causes or physiological disorders • Extreme temperatures • Extreme soil wetness • Excess or lack of light • Oxygen deficiency • Air pollution, exposure to emissions • Nutrient deficiency (macroelements (K,Ca), microelements (B)) • Inappropriate pH • Inappropriate agrotechnic management • The toxicity of pesticides • Toxicity of minerals CAUSES AND AGENTS OF PLANT DISEASES AND DISORDERS II. Infections (biotic) disease (and damage) • Viruses and viroids • Prokaryots (Bacteria and Phytoplasmas) • Fungi • Parasitic higher plants and green algae • Protozoa • Nematodes, mites, insects EXAMPLES OF ABIOTIC DISORDERS EXAMPLES OF ABIOTIC DISORDERS Frost damage of cherries (Prunus) Drought in Spruce (Picea) Ozone damage on Nicotiana tabacum INFECTIOUS AGENTS OF DISEASES . Bionosis – infectious diseases . A. NON-CELLULAR ORGANISMS A.1. Viroids A.2. Viruses . B. PROKARYOTIC ORGANISMS B.1. Bacteria B.2. Phytoplasmas . C. EUKARYOTIC ORGANISMS C.1. Fungi C.2. Algae C.3. Higher plants C.4. Protozoa C.5. Nematodes, mites, insects MORPHOLOGY AND WAYS OF MULTIPLICATION OF SOME OF THE GROUPS OF PLANT PATHOGENS SCHEMATIC DIAGRAM OF THE VARIOUS PLANT PATHOGENS IN HOST CELL A.NON CELLULAR ORGANISMS A.1. Viroids . Uncoated, small, circular, single-stranded RNA, which replicated autonomously when inoculated into a host plant. They differ from viruses or bacteriophages by absence of a protein capsid and a small genom. The smallest known agents of infectious plant diseases. Discovered to r. 1971, until most of the diseases caused by viroids were considered to be viral diseases. It is not known how viroids actually replicate probably all components necessary for their replication provides host. Pathogenesis modifies metabolic regulatory networks, the transcription of a number of genes, transcription factors and their ability to activate promoters A.NON CELLULAR ORGANISMS A.1. Viroids . Most of viroids is localized in the nucleus of the host cell, usually they are transmitted by sap (míza) also by pollen or vegetatively. They are resistant to high temperatures. Most of viroids causes in the infected plants no symptoms. General symptom of infected plants are dwarf growth, epinastic deformation and creased leaves. To date, it was found that around 40 different plant diseases are caused by viroids. Viroids act only disease in plants. They were not found in animals and humans. Taxonomy of viroids Avsunviroid (ASBVd)-replication occurs in chloroplasts Pospiviroid (PSTVd)- replication occurs in nucleus Unassigned viroides SYMPTOMS CAUSED BY VIROIDS Potato spindle tuber disease Chrysanthemum stunt disease Examples of diseases caused by viroids POTATO SPINDLE TUBER - Potato spindle tuber viroid (PSTVd)– It causes big losses, attacks all varieties and is spreading rapidly CITRUS EXOCORTIS CACANG- (Citrus CADANG of exocortis COCONUT PALM viroid) (Coconut cadang- cadang CCCVd) – On Phillipines devastates coconut palms CHRYSANTHEMUM STUNT (Chrysanthemum stunt viroid – CSVd) A. NON CELLULAR ORGANISMS B. A. 2. Viruses . Obligate parasites reproducing only in host cells (replication is dependent on the host cell). They usually have a very narrow host range. They attack all species of living organisms, distinguish plant viruses, animal viruses and bacteriophages (viruses on bacteria). Recently it is described about 2000 species of viruses, half of them infecting the plant. Diseases caused secondly disturbance of metabolism in the cells and the use of energy in cells. STRUCTURE OF VIRAL PARTICLES • Virion - virus particles, which is composed of protein and one type of nucleic acid (ss RNA, ds RNA, ss DNA, ds DNA) • Protein component - capsid not only protects the nucleic acid, but generally increases the infectivity of the virus ELECTRON MICROPHOTOGRAPHS OF DIFFERENT MORPHOLOGICAL TYPES OF VIRUSES A. NON CELLULAR ORGANISMS B. A. 2. Viruses . TRANSFER - viruses get into cells mostly through injuries or transmission of sucking insects, nematodes, by fungal vectors (Polymyxa, Spongospora, Olpidium), seeds, pollen, vegetative propagation. In the plant virus spreads by plasmadesm and then by the vascular bundles. SATELIT VIRUSES They represent the highest level of parasitism. These are virus particles, which can not occur separately, but only with a different virus particles - in the tobacco mosaic virus (Tobacco necrosis satelite virus). Their replication is dependent on the synthesis of viral RNA. PROTECTION AGAINST VIRUSES - quarantine: control of vectors - insects, using clear seeds, virus inactivation by heat. It is not yet known chemical control. PLANT VIRUS TRANSMISSION PLANT VIRUS TRANSMISSION II. INSECT VECTORS OF PLANT VIRUSES TRANSMISSION OF PLANT VIRUSES BY NEMATODES, MITES AND FUNGI SYMPTOMS OF VIRUSES ON PLANTS LEAVES – chlorotic or VIRAL PLANT – growth retardation, necrotic lesions, mosaic, vein dwarfism, shortened internodes, wilting yellowing, stripes, deformaiton FLOWERS - the colorfulness of the flowers, streaking Histological symptoms – hyperplasy, hypoplasy, necrosis Cytological changes – formation of incluses SYMPTOMS OF VIRUSES ON PLANTS SYMPTOMS OF VIRUSES ON PLANTS CURRENT PLANT VIRUSES TAXONOMY I: Single-stranded (+)sense DNA (+ ssDNA) single stranded DNA II: Double-stranded DNA with RNA intermediate (ds DNA (RT) (double stranded DNA, replicates using reverse transcriptase) III: Single-stranded (+)sense RNA (+ ssRNA) single stranded RNA (replicate using polymerase; RNA with function m-RNA) IV: Single-stranded (-)sense RNA (-ssRNA) single RNA complementary to m-RNA V: Single-stranded (+)sense RNA with DNA intermediate in life-cycle (ssRNA (RT)) single stranded RNA (replicates using reverse transcriptase) VI: Double-stranded RNA (dsRNA) double stranded RNA REPRESENTATIVE EXAMPLES OF INDIVIDUAL GROUPS OF VIRUSES I. ssDNA – single stranded DNA - Geminiviridae – Maize streak virus (MSV) On maize (Zea mays) II. (ds DNA (RT) double stranded DNA, replicates using reverse transcriptase Cauliflower mosaic virus (CaMV) – on cauliflower (Brassica oleracea var. botrytis) III. (+) sense ssRNA viruses (single stranded RNA (replicate using polymerase; RNA with function m-RNA) Bromoviridae, Caliciviridae, Comoviridae, Coronaviridae (Pea enation mosaic virus), Potyviridae (Potato virus Y), Flaviviridae, Leviviridae (Tobacco necrosis virus, Barley yellow dwarf virus), Sequiviridae, Tetraviridae (Tobacco mosaic virus), Tombusviridae Tobacco mosaic virus (TMV) Pea enation on tobacco (Nicotiana tabacum) mosaic virus Barley yellow dwarf (PEMV) – on pea luteovirus (BYDV) (Pisum sativum) on barley (Hordeum vulgare) IV. (-) sense ssRNA viruses – single RNA complementary to m-RNA Rhabdoviridae (Lettuce necrotic yellows virus), Bunyaviridae, Orthomyxoviridae. Lettuce necrotic yellows virus (LNYV) - on lettuce (Lactuca sativa) V. ssRNA (RT) single stranded RNA (replicates using reverse transcriptase) Pseudoviridae VI. ds-RNA – double stranded RNA - Reoviridae Rice ragged stunt virus (RRSV) on rice (Oryza sativa) B. PROKARYOTIC ORGANISMS ONLY REPRESENTATIVES OF GROUP BACTERIA CAUSE PLANT DISEASES B. TAXONOMY of BACTERIA BACTERIA AS PLANT PATHOGENS GRACILICUTES (GRAM-NEGATIVE BACTERIA) CLASS: PROTEOBACTERIA (families Enterobacteriaceae (Erwinia), Pseudomonadaceae (Pseudomonas, Xanthomonas), Rhizobiaceae (Agrobacterium) FIRMICUTES (GRAM-POSITIVE BACTERIA) CLASS ACTINOBACTERIA Streptomyces, Clavibacter CLASS FIRMICUTES (Bacillus, Clostridium) MOLLICUTES (Spiroplasma, Phytoplasma) BACTERIAL TAXONOMY • Bacterial /Archaeal species are defined on the basis of phenotypic and genotypic differences. • A bacterial strain is a population of organisms that descends from a single organisms or pure culture • A bacterial species is a collection of strains that share main stable characteristics and differ significantly from other groups of strains BIOVARS – differ biochemically or physiologically MORPHOVARS – differ morphologically SEROVARS – differ in antigenic properties B.1. BACTERIA . Prokaryotic organisms, their DNA is not coated by nuclear membrane. Do not contain membrane organelles (mitochondria, nucleus, plastids ..) . They have cell walls (one exception representatives of - Mollicutes). They have tremendous ability of propagation (usually division, and budding) . They occur mainly in warm and moist areas . Expansion of bacteria - water, insects, animals, humans . MORPHOLOGY OF BACTERIA - bacteria can be rod-shaped, oval, spiral, fibrous, with flagella or without flagella, they can produce spores or not. Protein capsid. Nucleoid - a circle of DNA; plasmids. .DETERMINATION OF BACTERIA : shape, number and location of flagella, Gram stain, infestation symptoms (wilting, spotting), cultivation - shape, coloration of colonies, biochemical tests, serology, molecular identification methods – RFLP, PCR. MORPHOLOGY OF BACTERIA Rod-shaped (A), oval (B,C,D), spiral (E), fibrous (G) G Monotricha Number of flagella: monotrichous (1), polytrichous (more than 1) The arrangement of flagella: monopolar, bipolar, lofotrich, peritrich, amfitrichal, atricha Polytricha Monopolar Peritrich Lofotrich Amfitrich (bipolar lofotricha) MEANS OF DISSEMINATION OF BACTERIA (AND FUNGI) SYMPTOMS OF BACTERIA Discoloration INFECTION ON PLANTS Anthracnosis, necrosis Clavibacter michiganense wallnut Xanthomonas campestris Bacterial wilting - break down the walls of the xylem Pseudomonas syringae pv. lachrymans
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