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lecture14 - Disease development in plant populations...

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1 Disease development in plant populations Agroecosystems vs Natural ecosystems Agro-ecosystems vs Natural ecosystems Ecosystem – smallest ‘functional' unit; an ecological community (organisms and their environment) considered to function as a unit; independent via interdependence Agriculture exists as a type of ecosystem agro-ecosystem Natural ecosystems Do plant diseases occur in natural ecosystems? Yes, but over a long time period, may either cause less damage than diseases in agroecosystems, or we are not as concerned about a low to moderate level of disease in a group of plants we are not trying to obtain some type of economic return from. We are concerned when ecosystems are severely affected: Jarrah decline in Australia Chestnut blight in the USA Sudden oak death in California
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2 Agro-ecosystems Agro-ecosystems are relatively static , with little or no evolution (change), with the natural stabilizing mechanisms disregulated by man . In agroecosystems, we must constantly start over to get the desired output (yield). They have uniform, pioneer vegetation with very little diversity, which leads to potential instability; the stability observed in agro- ecosystems is ‘bought' by energy inputs . Agro-ecosystems 1) increased density of hosts 2) increased genetic uniformity of plants and development of highly adapted cultivars with complete resistance genes vs land races [old roses; asparagus, etc] with high levels of partial resistance to many pathogens and problems 3) decreased microbial diversity – monoculture, pesticides Examples of Disease Cycles • Monocyclic Disease – Verticillium wilt • Polycyclic Disease – Apple scab • Polyetic – Dutch Elm disease
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3 Verticillium Wilt – A monocyclic disease with no spores Apple Scab – A polycyclic disease with sexual and asexual spores Early Blight of Tomato – A polycyclic disease with only conidia
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4 Take-All patch – A polycyclic disease without spores Dutch Elm Disease – Cycle over years involving vector Host-Pathogen Systems • Southern corn leaf blight – genetic uniformity • Chestnut Blight – exotic pathogen • Dogwood Anthracnose • Ergot of Rye – mycotoxins; sociological and historical affects • Sudden Oak Death – introduced pathogen affecting natural and agricultural systems • Stem Rust of Wheat (lab)
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5 Southern corn leaf blight From minor disease to major epidemic From around 2% loss in 1969 to 80% in many areas in 1970. Southern Corn Leaf Blight devastated 15 percent of America's 1970 corn crop, reducing the average national corn yield from 84 to 72 bushels per acre, costing farmers about $1 billion in losses. Southern corn leaf blight - caused by Cochliobolus heterostrophus, a member of the Ascomycota . Also has an asexual stage known as Bipolaris maydis , a member of the Deuteromycota - mycelium and spores overwinter in soil and crop debris. -spores±are
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This note was uploaded on 03/22/2008 for the course PP 315 taught by Professor Shew during the Spring '08 term at N.C. State.

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lecture14 - Disease development in plant populations...

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