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Home , Oomycete

in lab tomorrow

• Quiz (Lab manual pages 1-5 ‘field trip’ and page 27 ‘ intro’ • Microscope tutorial • Look at Oomycete diseases – signs and symptoms • Disease of the week ‘Unknown’ – worksheet to fill in

Oomycetes (water ) • Stramenophiles ( ) • Diploid (2N) – most non- • Hyphae are coenocytic (tubes) • made of • Sexual reproduction: oospore • Asexual reproduction: sporangia and

Eukaryotes

1 Oomycota

Eukaryotes

University of California Museum of Paleontology

Important diseases caused by Oomycetes Soilborne • damping-off • Pythium blight of turf • root rots Foliar • Late blight of /tomato

• SuddenR death •Downyo mildews o t

2 Damping-off caused by Pythium spp. Favored by cool, wet soils that slow emergence The is ubiquitous & opportunistic

3 Pythium damping off is favored by cool, wet soils

Pythium blight of turf

Pythium spp. are opportunists – they aggressively colonize dying 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. recently stressed, or lush from high N show increased susceptibility.

4 Phytophthora root rots (aggressive pathogens)

Phytothphora of rhododendron

5 6 Oospores Typically, oospores (long- lived resting ) play an important role in soil- borne diseases

With foliar pathogens, oospores are commonly rare and may not be necessary for disease to occur

7 Oospores (and clamydospores) are very long lived in soil but generally are not easily dispersed

Truck wash in S. Oregon National Forest for the purpose of ………?

Oospore • Sexual reproductive of an Oomycete • Thick, double-walled, survival spore • Develops from the merging of an antheridium and an • Typically, it germinates to form a zoosporangium

8 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’

9 Foliar Oomycetes

Tan Oak with Ramorum Blight (Sudden Oak Death)

10 Late blight of potato

11 Downy Mildew of lettuce

sporangia and zoospores • Asexual structures () • Zoospores are born in the • Foliar oomycetes: sporangia dehisce (i.e., become windborne spores) • Zoospores require water for movement (saturated soil, wet leaf surface) • Zoospores attracted to plant exudates

12 13 Sporangia of

14 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, ?

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