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Definitions

Definitions. Propagule= structure used by an organism to spread or survive Locus= a physical portion of a chromosome,a gene Intron= a portion of DNA , a locus that does not code for a protein Exon= a coding gene. Definitions-2. Alleles= different DNA sequences at the same locus

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Definitions

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  1. Definitions • Propagule= structure used by an organism to spread or survive • Locus= a physical portion of a chromosome,a gene • Intron= a portion of DNA , a locus that does not code for a protein • Exon= a coding gene

  2. Definitions-2 • Alleles= different DNA sequences at the same locus • If a locus has variation in sequence it is polymorphic (many forms) • Polymorphisms are differences in DNA among organisms, the more polymorphisms the easier it is to differentiate organisms • There are more polymorphisms in introns

  3. Definitions-3 • Invasive organisms: exotic organism that reproduces and occupies progressively a larger area: • Fast reproductive cycle • Vectored • Hardy • Occupy unoccupied niches • Different drain on natural resources • Make environment favorable for itself and other invaders • Linked to disturbances • If pathogen , more changes because top of pyramid • May hybridize with native species: new taxon is created

  4. MICROBIAL INVASIONS OF NATURAL ECOSYSTEMS: • Cannot be eradicated • Problematic because not noticeable for decades • Can cause limited problems • Can cause major alterations: Because of lack of coevolution between host and pathogen Because they are where similar organisms were not before

  5. Introduced organisms • Have a smaller genetic variation than original population • Strong founder effects • Each founder can create a significantly different population if not in equilibrium • Mating will homogenize variation • Mating barriers will increase difference

  6. How does DNA help • Identify microbe • Determine whether equally named organism from elsewhere is the same or not • Determine how it is reproducing • Quantify organism • Determine whether it is hybridizing or not

  7. Definitions • Phylogeny • Phylogeography • Gene geneaology

  8. DISEASES AND TREES • What exactly is a disease? It is the outcome of an interaction between a plant and the environment, resulting in an altered physiology of the host • Sustained interaction=biotic • Single event= abiotic

  9. What is a pathogen? • Strictly speaking a pathogen is the causal agent of disease • Bacteria • Viruses • Nematodes • Stramenopiles • Algae • Phytoplasmas • Higher plants

  10. Nematodes

  11. And of course… fungi • Fungi: saprophytic, symbionts, and pathogens • Polyphyletic group in evolutionary terms • Basidiomycetes Ascomycetes Zygomycets Animals Plants Red algae Brown algae Myxomycetes

  12. Diversity of fungi, but all have ideal structure for plant infection: • hypha/cord/rhizomorph/infection peg/appressorium • Sexual vs. asexual reproduction: can do both • Do not photosinthesize • Chitin in cell wall • Exogenous digestion • Indefinite growth • Phenotypic plasticity and pleomorphisms

  13. Septa Pores Pores CELLS

  14. Fungi… again! • ASCOMYCETES • BASIDIOMYCETES • OOMYCETES (fungus-like, water molds)

  15. ASCOMYCETES • Yeasts (fermentation, human mycoses) • Truffles, morels • Penicillia (penicillin), Fusaria (potent toxins, damping off of seedlings), molds

  16. Ascus is the sack in which the spores are contained

  17. Asci can be placed on a disk (apothecium), many apothecia can be together in a fruitbody Morel fruitbody

  18. Asci can be carried inside a flask (perithecium) Nectria

  19. Ploidy is mostly n

  20. BASIDIOMYCETES • Mushrooms. mycorrhizal • Wood decay organisms • Rusts, Smuts • Yeasts and damping off

  21. Toadstools and huitacochle are both basidiomycetes

  22. Basidium means “club”, it carries the basidiospores (dispersion propagules) naked

  23. Most of their life, they are n+n (dikaryons), some rare ones are diploid

  24. Oomycetes • Belong to the kingdom Stramenopila, used to be called Chromista • Phytophthora, Pythium, Saprolegnia H20

  25. Cellulose in cell wall Ploidy is 2n Result of sexual activity is oospore (2n) Meiosis, somatogamy, caryogamy all occur at the same time Water adapted biology, flagellate phase No septa, holocoenocytic hyphae Chitin in cell wall Ploidy is n, or n+n Result of sexual activity is a spore n Meiosis, somatogamy,caryogamy are usually interupted by vegetative (somatic phase) Better adapted for aerial transmission Septate hyphae Oomycetes are not fungi

  26. Phytophthora • Some important plant pathogens, with very well known history • Phytophthora infestans and the Irish potato famine • Phytopthora cinnamomi and the Jarrah dieback in Australia

  27. The Irish Potato Famine • From 1845 to 1850 • Phytophthora infestans • Resulted in the death of 750,000 • Emigration of over 2 million, mainly to the United States.

  28. Phytophthora: “plant destructor” • Best known pathogen whose long-distance transport linked to agriculture. • Infected root-stocks • Infested soil • Infected plants

  29. 70 species of Phytophthora • 60 until a few years ago, research accelerated, especially by molecular analyses • Differentiated on basis of: • Type of sexual intercourse • Type of sexual activity • Number of hosts • Ideal temperature • Type of biology • Evolutionary history (Waterhouse-Cooke)

  30. Hyphae, sporangia, and zoospores of P. ramorum

  31. Zoospore

  32. Hyphae, sporangia, and zoospores of P. ramorum

  33. Most of their lifecycle they are 2n Have cellulose in cell wall Not fungi!!, but look like them because of convergent evolution

  34. Fungi do not photosynthesize • Biotrophic: mycorrhyzae, rusts • Endophites: clavicipetaceae, • Necrotrophic; most pathogens • Saprobes: primary (involved in litter decomposition)

  35. DISEASE!! • Symptoms vs. signs; e.g. chlorosis vs. fruit-body • The disease triangle

  36. host-pathogen-environment • Susceptibility of individuals or of portions of individuals • Genetic variability • Basic compatibility (susceptibility) between host and pathogen • Ability to withstand physiological alterations

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