lecture15 - Plant Disease Epidemics Past and Present...

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1 Plant Disease Epidemics Past and Present Host-Pathogen Systems Southern corn leaf blight – new pathogen race based on genetic uniformity Chestnut Blight – exotic pathogen/natural forest ecosystem Dogwood Anthracnose – exotic pathogen/natural ecosystem Jarrah Dieback and Decline – exotic pathogen in a geographically isolated natural ecosystem Ergot of Rye – mycotoxins; sociological and historical impacts Sudden Oak Death – introduced pathogen affecting natural and agricultural ecosystems Late blight of potato – introduced crop and pathogen; sociological/economic impacts Stem Rust of Wheat (lab) Jarrah Forests Many of the open or dry sclerophyll forests of Western Australia are dominated by jarrah, tall eucalypts with a fibrous bark. These large, slow-growing trees are well adapted to survive in dynamic equilibrium with a climate that would not otherwise support a forest. The soils are poor, laterites with a low organic content and hence contain relatively few soil micro-organisms. The jarrah are adapted to survive a dry summer- autumn period, bushfires, and low fertility soils, especially low in phosphorus. Jarrah Dieback or Decline Jarrah dieback or decline, caused by Phytophthora cinnamomi, has been a major factor affecting South West Australia forest management and land use practice for over thirty years. This aggressive soilborne pathogen was introduced into Western Australia 1921, but only became established in the jarrah forests in 1965 . It is now present in other states on the continent. This fungus attacks nearly one thousand different plant species , including Euclayptus marginata (jarrah), and is also a major problem in horticulture, agriculture and forestry throughout the world. The damage caused by P. cinnamomi in Australian forest amounts to the destruction of whole plant communities, eliminating 50-70% of the species present , including both valuable timber trees and a whole array of brilliantly flowering woody shrubs that do not occur outside of Australia. The death of 59 indigenous species in 34 genera and 13 families has been recorded from infested jarrah forests. Jarrah Dieback Jarrah Dieback or Decline in Southwest Australia Jarrah Dieback Healthy forest vegetation Forest vegetation after Phytophthora cinnamomi is introduced
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2 Impacts of Jarrah Dieback • Death of trees - 45% • Death of 50 - 75% of the species present • Decline in total number of plants • Decline in plant diversity • Extinction of endangered species • Increase in % of bare ground • Change in vegetation to sedges and rushes • Loss of birds, marsupials, and insects - loss of habitat Management of Jarrah Dieback • During wet periods the forest may be closed to the logging industry to prevent introduction or spread of the pathogen. • Otherwise all vehicles and equipment must
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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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lecture15 - Plant Disease Epidemics Past and Present...

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