lecture 3

lecture 3 - 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 #3 How do pathogens infect and spread? The Disease Triangle and Disease Cycle RD Martyn, Purdue University 1 The Disease Triangle RD Martyn, Purdue University 2 1 8/27/10 The Disease Cycle RD Martyn, Purdue University 3 Monocyclic vs. Polycyclic Diseases •  Monocyclic – one infecLon cycle per season •  Polycyclic – MulLple cycles per season RD Martyn, Purdue University 4 2 8/27/10 Apple Scab Disease Cycle (Venturia inaequalis) RD Martyn, Purdue University 5 •  Monocyclic diseases –  Dutch elm disease (Ceratocyc1s ulmi) –  VerLcillium wilt (Ver1cillium albo ­atrum) –  Monosporascus root rot (Monosporascus cannonballus) •  Polycyclic diseases –  Coffee rust, soybean rust, wheat rust (Hemileia vastatrix, Phakopsora pachyrhizi, Pucinnia graminis f. sp. tri1ci) –  Late blight of potato & tomato (Phytophthora infestans) –  Apple scab (Venturia inaequalis) RD Martyn, Purdue University 6 3 8/27/10 How do plant pathogens infect? •  •  •  •  •  Right host Right inoculum Right place (infecLon court) Right Lme Right condiLons (environment) RD Martyn, Purdue University 7 How plant pathogens Infect •  Many plant pathogens infect plants in ways similar to how human and animal pathogens infect. 1.  Wounds •  physical damage (mechanical injury, •  breakage, pruning, wind, etc.) •  insect damage (chewing) •  animal damage (grazing, breakage, etc.) Beetle damage to sweet RD Martyn, Purdue University potato Deer feeding damage on corn 8 4 8/27/10 How do plant pathogens infect? 2. Natural openings –  Stomata –  LenLcles –  Hydrathodes –  Root juncLons –  Natural cracks RD Martyn, Purdue University 9 Stomate (stomata): An opening in the plant surface formed by a pair of guard cells that allows for gas exchange from the cells and the outside. Scanning electron microscopy of invasion of apple leaves and blossoms by Pseudomonas syringae pv. syringae. 1989. E. L. Mansvelt & M.J. Habngh. Appl. & Environ. Microbiol. 55:533 ­538. RD Martyn, Purdue University 10 5 8/27/10 ______________________ – Spongy openings in the surface of many plants that allow for the exchange of gases between the internal Lssues and the outside atmosphere. LenLcels on birch bark LenLcels on wild cherry LenLcels on apple RD Martyn, Purdue University 11 RD Martyn, Purdue University 12 6 8/27/10 Hydathodes – Specialized leaf structure used for secreLon or exudaLon of water (gugaLon); leaf opening at terminus of vein. RD Martyn, Purdue University 13 Natural cracks and Root juncLons SEM of watermelon seed Watermelon root Fusarium oxysporum growing on watermelon seed RD Martyn, Purdue University 14 7 8/27/10 How do plant pathogens infect? 3.  Direct penetraLon of plant surface (leaf, stem, root, fruit, flower, etc.) A. Fungi  ­  Adhesion of spore to plant surface  ­  GerminaLon and growth of germ tube  ­  FormaLon of infecLon peg  ­  FormaLon of infecLon structures (appressoria, hyphopodia, infecLon cushions, etc.) RD Martyn, Purdue University 15 Germ tube Spore Appresorium (ia) Leaf surface Infec&on peg Haustorium (ia) Fungal spore, germ tube & appressorium RD Martyn, Purdue University Hyphopodia 16 8 8/27/10 How do plant pathogens infect? 3.  Direct penetraLon B. Nematodes EctoparasLc EctoparasLc nematode feeding on a plant root via a stylet EndoparasLc RD Martyn, Purdue University 17 How do plant pathogens infect? •  Vectors  ­ AcLve vectors (most common with viruses, but also other types of pathogens) •  Insects (aphids, leakoppers, psyllids, beetles, etc.) •  Mites (Arachnids) •  Nematodes •  PollinaLng insects •  Fire blight of pome fruit (honey bees & Erwinia amylovora)  ­  Passive vectors RD Martyn, Purdue University 18 9 8/27/10 Aphids RD Martyn, Purdue University 19 Leakoppers RD Martyn, Purdue University 20 10 8/27/10 Passive vectors Fire blight of pears & apples Erwinia amylovora / honey bee RD Martyn, Purdue University 21 11 ...
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