Pythium characteristics checklist

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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