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lecture 4

lecture 4 - Introductory Plant Pathology BTNY 301 R....

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Unformatted text preview: 8/27/10 Introductory Plant Pathology BTNY 301 R. D. Martyn Fall, 2010 Lecture #4 How do pathogens cause disease? RD Martyn, Purdue University 1 How do plant pathogens cause disease? •  Diseases are a result of a pathogen disrupKng one or more physiological processes in the plant. •  Disease is conKnual. •  The effect may be synergisKc, in that more than one type of process may be affected simultaneously. RD Martyn, Purdue University 2 1 8/27/10 How do plant pathogens cause disease? 1. Cellular enzymes (cellulases, pecKnases, cuKnases, lignases, proteases …) RD Martyn, Purdue University 3 RD Martyn, Purdue University 4 2 8/27/10 Rots potato Chile pepper onion RD Martyn, Purdue University 5 How do plant pathogens cause disease? 2.  Phytotoxins – Metabolites produced by micro ­ organisms that are poisonous (toxic) to plants. a.  General toxins – toxic to many plants; virulence factors (contribute to the disease severity) Tabtoxin – Pseudomonas tabacii (disrupts phytosyn.) Syringomycin – Pseudomonas syringiae Fusaric acid – Fusarium oxysporum RD Martyn, Purdue University 6 3 8/27/10 How do plant pathogens cause disease? b. Host ­specific toxins – toxic to only a specific plant, species, or variety; pathogenicity factor (disease determinant) Victorin (HV toxin) – Oats [Biploaris victoriae] (Helminthosporium victoriae] T ­toxin – South. corn leaf blight [Bipolaris maydis ­ Race T] RD Martyn, Purdue University 7 How do plant pathogens cause disease? 3. Growth regulators (Hormones) – Molecules that influence growth processes and are acKve at very low concentraKons. –  Auxins –  Cytokinins –  Gibberellins –  Ethylene RD Martyn, Purdue University 8 4 8/27/10 Growth regulator disease symptoms •  StunKng (Dwarfing) / GiganKsim •  EKolaKon / elongaKon A. Stunted corn plants RD Martyn, Purdue University B. EKolated seedlings 9 Growth regulator disease symptoms •  Witches broom •  Leaf distorKons (crinkle, curling, etc.) C. Witches broom RD Martyn, Purdue University D. Leaf distortaKon (crinkle, curling, bending, etc.) 10 5 8/27/10 Galls Root knot nematode on carrot Crown gall RD Martyn, Purdue University 11 Growth regulator disease symptoms •  Galls –  Hypertrophy: Increase in cell size ☐  ­  Hyperplasia: Increase in cell number ! ! ! ! ! ! !# ! ! ! ! ! ! !# ! ! ! ! ! ! ! ! !# ! RD Martyn, Purdue University 12 6 8/27/10 How do plant pathogens cause disease? 4. Tyloses – EnvaginaKons of the xylem parenchyma cells resulKng in a “balloon ­like structure” that blocks the water flow. RD Martyn, Purdue University 13 Tyloses – Fusarium wilt of watermelon [Fusarium oxysporum f. sp. niveum] Healthly Micrographs by RD Martyn, copyright RD Martyn, Purdue University 14 7 8/27/10 DisrupKon of transpiraKon (Xylella [email protected]) Leaf scorch of oak Cells of X. fastidiosa in xylem vessels Mollenhauer & Hopkins. 1974. J. Bacteriol. 119:612-618 Pierce’s disease of grapes RD Martyn, Purdue University 15 How do plant pathogens cause diseases? 5. DisrupKon of phloem and nutrients Fungal cankers killing the cambium and phloem Phytoplasmas filling a phloem sieve element Phloem necrosis caused by potato leaf roll virus RD Martyn, Purdue University From G.N. Agrios. 2005. Plant Pathology, 5th Ed. 16 8 8/27/10 How do pathogens cause diseases? 6. Haustorium (ia) – an enlargement of the fungal hypha that invaginates the host cell membrane to absorb nutrients. Typical of obligate parasites (pathogens that cause late blight, downy mildew, powdery mildew, & rusts) Bracker, CE & LJ Littlefield. 1973. in: Fungal pathogenicity and the plant’s response. Academic Press, NY. RD Martyn, Purdue University 17 How do plant pathogens cause disease? 7. Increased cellular respiraKon. UKlizes food reserves more quickly and uncouples oxidaKve phosphorylaKon (no ATP produced) 8. Increases permeability of cell membrane (e.g., phytotoxins). Causes cellular leakage 9. Altered transcripKon (e.g., viruses) 10. Increased transpiraKon. DesiccaKon of Kssue RD Martyn, Purdue University 18 9 ...
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