Pythium characteristics checklist


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Date designation:__________________

Homothallic vs. heterothallic Sporangia diameter

Oogonia produced in single cultures (Homothallic)
Sporangia over 40 µm diameter

Oogonia produced in dual cultures (Heterothallic)
Sporangia less than 40 µm diameter

Oogonia not produced in single or dual cultures Hyphal swellings
Oogonia shape
Catenulate hyphal swellings present

Oogonia often irregularly shaped
Globose hyphal swellings present

Oogonial wall ornamented
Filamentous inflated hyphal swellings present

Oogonial wall smooth or occasionally with few projections Hyphal swelling diameter
Oogonia projection shape
Hyphal swellings large, often 30-40 µm in diameter

Oogonial projections acute
Hyphal swellings less than 30 µm in diameter

Oogonial projections blunt Chlamydospores

Oogonial projections cylindrical, irregular
Chlamydospores present

Oogonial projections widening or dichotomously branched at tip Antheridia

Oogonial projections conical, sometimes curved
Antheridia absent

Oogonial projections mammiform Antheridia branch origin
Oogonia projection length
Antheridia hypogynous

Oogonial projections less than 3 µm long
Antheridia monoclinous

Oogonial projections more than 3 µm long
Antheridia diclinous
Position of the oogonium Antheridia stalks branching

Oogonia intercalary
Antheridial stalks unbranched

Oogonia terminal
Antheridial stalks branched

Oogonia often catenulate Position of the antheridia
Oospores plerotic or aplerotic
Antheridia often sessile

Oospores plerotic or nearly so
Antheridia often intercalary

Oospores aplerotic
Antheridia terminal
Oogonia stalks Antheridia per oogonium

Oogonial stalks mostly curved toward the antheridia
Antheridia 1 per oogonium

Oogonial stalks straight
Antheridia up to 3 per oogonium
Number of oospores
Antheridia up to 6 per oogonium

Oogonia containing a single oospore
Antheridia up to 10 per oogonium

Oogonia often containing two oospores
Antheridia up to 15 per oogonium

Oogonia containing multiple oospores
Antheridia greater than 15 per oogonium
Oogonia diameter Antheridia contact with oogonia

Oogonia on average about 15 µm in diameter
Antheridia usually entwining the oogonial stalk and base

Oogonia on average about 21 µm in diameter
Antheridia making broad contact with oogonia

Oogonia on average 30 µm in diameter
Antheridia making apical contact with oogonia

Oogonia on average 40 µm or more in diameter
Antheridia applied lengthwise to the oogonia
Oospore wall Antheridia size

Oospore wall less than 1 µm thick
Antheridia small (less than 10x5 µm)

Oospore wall 1-2 µm  thick
Antheridia large or variable in size (greater than 10x5 µm)

Oospore walls up to 3 µm thick Antheridia distance from oogonium

Oospore wall 2-4 µm thick
Antheridia usually orginating immediately below the oogonium

Oospore wall more than 4 µm thick
Antheridia usually originating some distance from the oogonium

Oospores reticulate Antheridia shape
Oospore color
Antheridia bell-shaped or lobed

Oospores uncolored
Antheridia long cylindrical

Oospores yellowish
Antheridia wavy or furrowed

Oospores pale lilac
Antheridia globose or clavate
Sporangia unknown Antheridia stalk swelling

Sporangia unknown, sometimes hyphal swellings present
Antheridial stalks swollen
Sporangia shape
Antheridial stalks not swollen

Sporangia globose, ellipsoidal or irregular

Sporangia sometimes in sympodial succession arising from immediately below a sporangium Growth on cornmeal agar

Sporangia laterally sessile
No growth on cornmeal agar

Sporangia filamentous, not inflated
Growing well on corn meal agar

Sporangia filamentous, inflated Aerial mycelium on cornmeal agar

Sporangia filamentous inflated, forming lobes, diverticles, or toruloid
Aerial mycelium on corn meal agar profusely cottony

Sporangia inflated filamentous parts + discrete globose or pyriform elements
Some aerial mycelium on corn meal agar
Sporangia proliferation Maximum temperature of growth

Sporangia not proliferating
Maximum temperature below 40C

Sporangia proliferating
Maximum temperature above 40C
Sporangia complexes

Sporangia forming complexes

Sporangia single, not forming complexes