oomycetes (water molds) 4 - 10c.pdf · pdf file oomycota important diseases caused by...
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Oomycetes in lab tomorrowOomycetes in lab tomorrow
• Quiz (Lab manual pages 1-5 ‘field trip’ and page 27 ‘Oomycete intro’
• Microscope tutorial • Look at Oomycete diseases –
signs and symptoms • Disease of the week ‘Unknown’ –
worksheet to fill in
Oomycetes (water molds) • Stramenophiles (Kingdom Chromista) • Diploid (2N) – most species non-pathogens • Hyphae are coenocytic (tubes) • Cell wall made of cellulose • Sexual reproduction: oospore • Asexual reproduction: sporangia and
University of California Museum of Paleontology
Important diseases caused by Oomycetes
• Pythium damping-off • Pythium blight of turf • Phytophthora root rots Foliar • Late blight of potato/tomato • Sudden oak death • Downy mildews
R o o t
Damping-off caused by Pythium spp. Favored by cool, wet soils that slow emergence
The pathogen is ubiquitous & opportunistic
Pythium damping off is favored by cool, wet soils
Pythium blight of turf
Pythium spp. are opportunists – they aggressively colonize dying plant materials: thatch layers, green manures, etc. – in turf, the disease occurs when the weather is warm and the grass crowns and thatch layer are under water for a long period. Plants recently stressed, or lush from high N show increased susceptibility.
Phytophthora root rots (aggressive pathogens)
Phytothphora root rot of rhododendron
Oospores Typically, oospores (long- lived resting spores) play an important role in soil- borne diseases
With foliar pathogens, oospores are commonly rare and may not be necessary for disease to occur
Truck wash in S. Oregon National Forest for the purpose of ………?
Oospores (and clamydospores) are very long lived in soil but generally are not easily dispersed
Oospore • Sexual reproductive spore of an
Oomycete • Thick, double-walled, survival spore • Develops from the merging of an
antheridium and an oogonium • Typically, it germinates to form a
Homothallic: Self-fertile individual is ♂ and ♀ Heterothallic: Different isolates (i.e., individuals) required for oospore production individual is♂ or ♀
thus, two (or more) ‘mating types’
Tan Oak with Ramorum Blight (Sudden Oak Death)
Late blight of potato
Downy Mildew of lettuce
sporangia and zoospores • Asexual structures (mitosis) • Zoospores are born in the sporangium • Foliar oomycetes: sporangia dehisce
(i.e., become windborne spores) • Zoospores require water for movement
(saturated soil, wet leaf surface) • Zoospores attracted to plant exudates
Sporangia of Phytophthora
Sporangiophores of downy mildew pathogens
Oomycete questions: • What is the basic life cycle of an Oomycete? • What component(s) of the life cycle concern us
most when attempting to suppress: soil-borne Oomycetes? foliar Oomycetes?
• How does the life strategy of the damping off pathogen, Pythium, differ from the downy mildew pathogen, Peronospora?