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Important biotic disease causing agents.pptx
- 1. Lecture -3: Bioticdisease causing agents 1. viruses
- 2. Virus • Size: ultramicroscopic,visualization requires an electron microscope • Genome: RNA/DNA. Either single stranded or double stranded • Capsid/ protein coat: composed of protein subunits. Lipoproteins are also sometimes associated • Obligate parasite: Dependent on the host for all the functions plus the synthesis of nucleic acids and amino acids • Replication by assembly: dependent on assembly of new particles from pools of required components . • Vector required for transmission
- 3. Historical developments inplant virology 1. Tulipomani in 15th century Holland- tulip from Persia: “ development of Bizzare” 2. 1886: Adolf Mayer confirmed the primary principle of plant virology when working with TMV 3. Dmitri Ivanowski (1892) Beijernick (1898)- unique nature of viral pathogens- named vrus as “ contagium fluidium vivium”- a contagious living fluid 4. Stanley- crystallized TMV- 1946 Nobel prize for chemistry 5. Bawden and Pirie- precence of phosphorus 6. Fraenkel Conrat- isolated RNA-1956
- 4. What do viruseslook like Isometric: spherical and (depending on the species) from about 18nm in diameter upwards. E.g Tobacco necrosis virus, genus Necrovirus with particles 26 nm in diameter. Rod-shaped: about 20-25 nm in diameter and from about 100 to 300 nm long. E.g. Tobacco mosaic virus, genus Tobamovirus with particles 300 nm long.
- 5. Filamentous: usually about12 nm in diameter and more flexuous than the rod-shaped particles. They can be up to 1000 nm long, or even longer in some instances. E.g. Potato virus with particles 740 nm long. Geminate: twinned isometric particles about 30 x 18 nm. These particles are diagnostic for viruses in the family Geminiviridae which are widespread in many crops especially in tropical regions. The example here shows Maize streak virus, genus Mastrevirus. Bacilliform: Short round-ended rods. These come in various forms up to about 30 nm wide and 300 nm long. E.g Cocoa swollen shoot virus 28 x 130 nm.
- 6. Symptoms found inplants infected with virus 1. Local lesions 2. Symptoms affection reproduction – sterility and yield loss 3. Symptoms caused by growth abnormalities 1. stunning and dwarfing 2. Tumour and gall 3. Distortions 4. Enations 4. Symptoms based on changes in Chlorophyll or other pigments 1. Mosaics and mottles 2. Stripes and streaks 3. Ring spots and line patterns 4. Vein banding 5. Vein clearing
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- 17. • Plant –Bioticdisease agents- Fungi most prevalent • Mycology- Mycos = Fungus+ -logy = study • Systematic study- 250 yrs old Role of Fungus 1. Agents of decomposition 2. Fungi attack wood 3. Important in production of food 4. Toxins (mycotoxins)- source of antibodies, cyclosporine, vaccine, hormones, enzymes Fungi found consistently in association with particular plant disease are called fungal pathogens
- 18. Fungal characteristics • Afungus (Pl. Fungi) is a eukaryotic, heterotrophic, absorptive organism that develops a microscopic diffuse, branched, tubular thread called a hypha (Pl. hyphae). • A group of hypha is called mycelium. It makes up the vegetative (non- reproductive) body or thallus of the fungus • The hypha of most fungi are microscopic- 3-4 μm to 30 μm wide • Septa (cross walls) may or may not be present- Septate • Without cross walls are called as aseptate or coenocytic
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- 20. • Hypha boundby cell membrane- plasmalemma- sterol- ergosterol • Outside the plasmalemma –Gylcocalyx Ascomycota, Basidiomycota, and Deuteromycota- Chitin (β- (1→4) linkage of n-acetylglucosamine) and glucans (long chains of glucosyl rediues) are major cell wall component. Zygomycota contains chitosan, chitin and polyglucuronic acid Oomycota contains- cellulose (β- (1→4) linkages of glucose • Chitin, glucans and cellulose form strong fiber called as microfibrils embedded in a matrix of glycoprotein and polysaccharide • Cell wall also contains dark pigments such as melanin
- 22. • Fungal cellsmay contain one or many nuclei. • A hyphal cell with genetically identical haploid nuclei is monokaryotic. • A cell with 2 genetically different but compatible haploid nuclei are dikaryotic (characteristic feature of Basidiomycota) • Plasmids present • Vacuoles-storage • Carbon reserve- lipids, glycogen, trehalose • Mitochondria present- varies in size
- 23. • Fungal celldfrom different hyphal strands fuse in a process called anastomosis- results in formation of Rhizomorphs, sclerotia (A sclerotium (plural sclerotia) is a compact mass of hardened fungal mycelium containing food reserves) and fruiting structures such as sporocarps
- 24. Types of fungalpathogens Saprophytes: use nonliving organic matter as a source of food Facultative saprophytes: Mainly parasites, but act as saprophytes between growing season Necrotrophs: usually saprophytes and survive well as sclerotia, spores or as mycelia but given the opportunity they become parasitic. Biotrophic pathogens (Obligate parasites): grow or reproduce only on or within a suitable host Mutualist biotrophic: Mycorrhiza and endophytes Hemibiotrophes: function as both Biotrophs and Necrotrophs
- 25. Disease symptoms causedby Fungus 1. Necrosis 2. Permanent wilting 3. Abnormal growth 4. Leaf and fruit abscission 5. Replacement of host tissue 6. Mildew
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- 37. Crown rot orroot rot or collar rot
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- 42. Vascular wilt 2. Permanentwilting
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