Stramenopila
Distinguishing Characteristics
• Cell Walls have Cellulose (-1,4 glucose linkage) vs. glucans.
• Lysine biosynthesis is DAP (like plants), vs. AAA like true fungi
• Heterokont- biflagellate-- anterior tinsel and whiplash flagella (vs. lateral
whiplash).
• Aquatic and soil fungi.
Stramenopila
 Other Characteristics
 Motile spores formed in a sporangium
 Sexual reproduction by gametangial contact
 Diploid through most of the life cycle
 Somatic structures are unicellular and holocarpic, or
rhizoidal, or coenocytic.
The Hyphochitryomycota
 Anterior tinsel flagellum
 Aquatic habitat
 Some parasites (on algae and fungi), others saprobes
 Thallus is holocarpic or eucarpic
 Holocarpic species are endobiotic
 Eucarpic species may be mono- or polycentric
 Zoosporangia are inoperculate, zoospore release is
through a discharge tube
Eg. Rhizidiomyces apophysatus
The Oomycota
 Zoospore biflagellate, heterokont—posterior facing
whiplash, anterior facing tinsel (emerge adjacent)
 Sexual Reproduction by gametangial contact
 Oogamous—two different types of gametangia, contact,
contents of one flow into the other
 Oospore is the sexual spore--thick walled resting spore
 Meiosis occurs in gametangium
 Haplobiontic (only diploid thallus, no haploid thallus)
 Some are holocarpic, no mycelium
 Some are eucarpic, but monocentric with rhizoids
 Some produce extensive mycelia with coenocytic hyphae
Oomycota
(5 orders, 65 genera, 500-800
species)—two we will discuss:
Peronosporales
Saprolegniales
Saprolegniales
long terminal sporangia with more than one egg per
oogonium
 “Water molds” occur abundantly in clean water. Mostly saprobes
but a few parasites (Saprolegnia parasitica) causes diseases of fish
and fish eggs.
 Most are hermaphroditic and homothallic (self-fertile).
 May be mono- or dimorphic (two spore forms)
Eg. Saprolegnia
Sexual Reproduction in the
Oomycota
Eg. #2 Achlya bisexualis
Very similar asexual phase
Unique sexual phase
Studied by John Raper in the 40’s and 50’s demonstrating a complex hormone system
involved in sexual development
Hormone
A
B
C
D
Source
Female somatic thallus
Male thallus w anther init.
Oogonial initials
Antheridia
Function
Induces antheridial branches
Induces formation of oogonial initials
Attracts anther branches
Oogonium & oospere differentiation
Achlya
Peronsporales
oval-lemon shaped zoosporangia with one oosphere
per oogonium
 Well developed coenocytic mycelium
 Most advanced and specialized order of the Oomycota
 All members are monomorphic (one type of zoospore)
 Three Families- distinguished by the structures that bear
sporangia
Families in the Peronosporaceae
 Pythiaceae- sporangia directly borne on vegetative hyphae.
These fungi are saprophytes or facultative parasites (very
destructive)
 Peronsoporaceae- sporangia borne on branched, determinate
sporangiophores (protrude through stomates). Obligate
parasites called the “Downy Mildews”
 Albuginaceae- chains of sporangia on club shaped
sporangiophores that rupture host epidermis to form a white
crust on leaf surface. Obligate parasites called “White Rusts”.
Ex. Pythium Debaryanum
Pythium Asexual
Zoosporangia
Pythium Sexual Reproduction
Pythium Oospores
‘Damping Off’ (Pythium)
Phytophthora
Phytophthora- a devastating
facultative parasite
Zoospore Release in
Phytophthora sojae
Quic kT ime™ and a Sorens on Video dec ompres sor are needed to see thi s pic ture.
Peronosporaceae- the ‘Downy
Mildews’
 Obligate parasites
 Branched, determinate
sporangiophores
 Sporangiophores protrude
through host stomates
Ex. Plasmopora viticola
(Peronosporaceae)
Downy Mildew on Grape
Albuginaceae- the ‘White
Rusts’
 Obligate parasites
 Club shaped sporangiophores (inside host leaf)
 Sporangia rupture leaf epidermis and appear as a white
crust
Ex. Albugo cadida
(Albuginaceae)