Fig. 3.14 Morphology of Pythiaceae s. lat.(a–g) Draw-
ings ofLagena radicola infecting cereal root cells.
Although unsequenced, it is thought to be a pythiaceous
genus. Series of drawings showing infection from cysts
and early (a) and more advanced stages (b) of thallus
development. Vesiculate discharge of spore mass (c)and
liberation of fully differentiated zoospores (d). Sexual
reproduction brought about by conjugation and migra-
tion of cytoplasm from male (antheridial) to female
(oogonial) thalli (e,f). Mature oospores within root cell
(g). From Karling ( 1981 ) after Vanterpool and Ledingham
( 1930 ). (h–j)Myzocytiopsis lenticulareinfecting rhabdi-
tid nematodes. Segmented thallus that has differentiated
into sporangial compartments, some of which are
showing vesiculate differentiation of zoospores (h). Adja-
cent antheridial and oogonial compartments (i). Fully
mature oospore showing stellate ornamentation of thick
wall (j). Adapted from Karling ( 1981 )basedonpapersby
Barron ( 1976 ). (k–w) Drawings ofPythiumspp. Eucarpic
hyphae of aPythiumsp. in cress-seedling hypocotyls (k).
Filamentous sporangium of P. porphyrae (clade A)
showing extra-sporangial vesicle in which zoospores dif-
ferentiate (l). Inflated filamentous toruloid sporangium of
P. aphanidermatum(clade A) before (m)andafter(n)
vesicle formation. Sequence illustrating formation of
zoospores within extra-sporangial vesicle (o–q). Papillate
and discharged ovoid sporangia ofP. multisporum(clade
E) (r).Internally proliferating ovoid sporangia ofP. undu-
latum(clade H) (s). (t–v) Single-oospored oogonia of
Pythiumspp. showing both smooth and spiny wall orna-
mentation:P. debaryanum(clade F) (t),P. amasculinum
(clade D) (u),P. ultimum(clade I) (v). Germinating ofP.
ultimumoospore showing vesiculate release of zoospores
(w). (l–o,t,v,w) All adapted from Webster (1980); (w)
based on original by Drechsler ( 1960 ). (k,r,s,u)Adapted
from Van der Plaats-Niterink ( 1981 )Systematics of the Straminipila: Labyrinthulomycota, Hyphochytriomycota, and Oomycota 67