Phylum Ascomycota (including Truffles) Flashcards
What % of described fungi are Ascomycetes?
~75%
What is the fruiting body of an Ascomycete called?
ascoma or ascocarp
What is an ascus (asci pl.)?
the sac like structure growing from the mycelium that produces ascospores
the defining feature of Ascomycetes
What are the sexual spores of Ascomycetes called?
ascospores
What is the defining feature of Ascomycetes?
asci (ascus s.)
Are ascospores motile?
no
What n type of mycelium does an ascoma have?
both dikaryotic (n+n) and haploid (n) mycelium
Where do asci form within an ascoma?
the dikaryotic hyphae
What is the apical cell of the dikaryotic hyphal tip of the ascoma where asci form called?
Crozier
What steps are involved in forming ascospores? How many are typically formed?
within the apical hyphal tip of the dikaryotic mycelium in the ascoma,
karyogamy and meiosis followed by mitosis produces 8 haploid ascospores
How are ascospores dispersed?
wind or animal/insect vectors
How does ascus development differ from basidium development?
asci are produced by a dikaryon that undergoes karyogamy and meiosis followed by one mitotic division = 8 haploid ascospores
basidia are produced by a dikaryon that undergoes karyogamy and meiosis only = 4 haploid basidiospores
Ascomycetes undergo one round of MITOSIS = 8 spores (n)
Basidiomycetes do NOT undergo mitosis = 4 spores (n)
T or F: Ascomycetes do not undergo mitotic division and usually produce 4 haploid spores
false!! they do have mitosis and produce 8 haploid spores
What are the sporangia of Ascomycetes called?
Asci (pl.)
Ascus (s.)
What are the 4 types of ascoma?
apothecial
perithecial
pseudothecial
cleistothecial
What is the hymenium?
the outer surface of the ascoma that is lined with asci
Describe apothecial ascoma and give an example
the hymenium (fertile layer) is exposed and curved in a cup-shape to release many asci at once for wind dispersal (ex. cup fungi)
ex. Ascobolus sp., Peziza sp.
Describe perithecial ascoma and give an example
the hymenium is enclosed but has a small opening to release one or few asci at a time via a sticky liquid to be dispersed by animal/insect vectors
ascoma is on host tissue surface or within stroma
ex. Claviceps purpurea (ergot fungus)
Describe pseudothecial ascoma and give an example
the hymenium is completely enclosed and the ostiole (opening) and ascoma are within the host stroma
ex. Venturia inaequalis (apple scab). Phaeocryptopus gauemanni (Swiss needle cast disease on Dfs)
Describe cleistothecial ascoma and give an example
no opening for ascospores to be released and instead the ascoma will decompose at maturity to be dispersed by animals/insects when consumed
ex. truffles, Tuber sp.
What are the 4 ascus types?
unitunicate-operculate
unitunicate-inoperculate
prototunicate
bitunicate
describe unitunicate-operculate asci. what type of fungi have these/give an example?
a single wall with a lid/operculum that opens at maturity to shoot out spores for wind dispersal
only in apothecial ascoma fungi - ex. cup fungi like Peziza sp.
describe unitunicate-inoperculate asci. what type of fungi have these/give an example?
a single wall with an opening at the top (no operculum/lid)
uses an elastic ring mechanism to shoot out individual spores for wind dispersal
found in perithecial and some apothecial
ex. Xylaria polymorpha (dead man’s fingers), a club fungus
describe prototunicate asci. what type of fungi have these/give an example?
no active spore-shooting mechanism - ascus wall dissolves and releases spores either by oozing out of ascoma or only if disturbed
usually cleistothecial and some perithecial
likely a feature that has evolved several times
ex. Elaphomyces muricatus (deer truffle) hypogeous
dispersed by mammals
describe bitunicate asci. what type of fungi have these/give an example?
double-walled (thin, rigid exterior and thick elastic inner)
outer wall splits and allows inner wall to absorb water and push spores upward (Jack in the Box)
ex. Ventura inequalis (apple scab) - pseudothecial ascoma
T or F: bitunicate and unitunicate asci are similar
false, they are very different mechanisms for releasing spores and likely diverged early
What occurs within the ascus?
nuclear fusion (karyogamy) and meiosis in teleomorphs and mitosis to produce 8 haploid ascospores
Define anamorph
the asexual phase of an Ascomycete
Define teleomorph
the sexual phase of an Ascomycete
Define holomorph
the complete life cycle (anamorph + teleomorph)
T or F: most Ascomycetes have a ‘perfect’ or complete holomorph
false! only ~15% of teleomorphs have been linked to an anamorph
Which are Ascomycetes more commonly known as, their anamorph or teleomorph?
anamorph - some sexual stages have not been observed
Why does the presence of anamorphs and teleomorphs make taxonomy challenging?
anamorphs and teleomorphs have distinct morphology and may have distinct ecological roles = same species assigned multiple names
Which stage produces the conidia?
anamorph
What is a conidia?
the asexual spores produced by anamorphs
portions of hyphae that are modified for survival and dispersal
Give an example of an ascomycete that has only been defined by its teleomorph
Sclerotinia sclerotiorum - causes stem rot in canola and is only known for its persistent sclerotia
Why is it so uncommon for anamorphs and teleomorphs to be connected?
they are usually spatially (different ecological conditions) and temporally (seasonally) distinct
they may grow in different seasons, with different hosts, or under different conditions
they may be morphologically distinct
How do anamorphs that have not been linked with a teleomorph or do not have one create genetic variability?
heterokaryosis and/or the parasexual cycle (non-meiotic processes)
Describe heterokaryosis
one process by which anamorphs with no teleomorph to undergo meiosis can produce genetic variability:
when there is more than one type of nucleus in a mycelium (either n or n+n), the hyphae might undergo anastomosis (like grafting?) with other genotypes
does not produce a true dikaryon
Describe the parasexual cycle
one process by which anamorphs with no teleomorph to undergo meiosis can produce genetic variability:
heterokaryosis followed by karyogamy to give a somatic diploid nucleus which then undergoes mitotic recombination
this is very rare
ex. Aspergillus, Candida albicans a human pathogen
What is the importance of the parasexual cycle in anamorphs?
it causes genetic variability in otherwise non-meiotic recombining anamorphs - usually clonal growth
some human pathogens like Candida albicans reproduce this way
T or F: some ascomycete anamorphs have basidiomycete teleomorphs
true
How are anamorphs different from zygomycetes?
zygomycetes have clear asexual and sexual stages described usually
T or F: one teleomorph may be linked to multiple anamorph species
true (ex., multiple plant hosts for a plant pathogen exist)
Describe the dutch elm disease example of a linked anamorph and teleomorph
Ophiostoma ulmi - teleo
Graphium sp. - anamorph
(not even same genera)
cause Dutch elm disease
O. ulmi uses bark beetle as a vector to enter the inside of the tree (difficult to penerate elm bark)
inside can become anamorph Graphium sp. and asexually reproduce to increase spread and infection
Describe the ergot fungus on rye grain example of a linked anamorph and teleomorph
Claviceps purpurea - teleo produces ascospres on sclerotia on the rye grain for reinfection
Sphacella segetum - anamorph grows on rye flowers in spring that were colonized by ascospores
Describe sclerotium
the compact, hardened mycelial mass that contains energy reserves for persistence during suboptimal conditions
How are anamorphs morphologically classified?
conidia production (in an enclosed structure or not)
conidia appearance
conidiogenesis (formation of conidia)
conidiophore aggregation (arrangement)
What are the 2 morphological categories for the structures that form conidia?
hyphomycetes: anamorphs with conidiophores directly on their substrate - no enclosure
coelomycetes: anamorphs with enclosed conidiophores
- pycnidium: conidia completely enclosed
- acervulus: conidia surrounded only around the bottom
What are conidiophores?
the reproductive structures that produce conidia
In what ways can conidia appearance vary?
size, shape, number of septa, surface ornamentation, appendages, colour
How are conidia structure, size and shape determined?
by the method of dispersal
What is the main diagnostic feature of conidial fungi (anamorphs)?
conidial morphology
What are the 7 types of conidial morphology?
amerospore
didymospore
phragmospore
dictyospore
scolecospore
staurospore
helicospore
Why is understanding conidiogenesis important for anamorph taxonomy?
conidia with similar morphology may have developed by a different process and therefore be different taxa
What are the 2 basic types of conidiogenesis?
blastic
thallic
Describe blastic conidiogenesis
conidium differentiation has already occurred at the hyphal tip when the cross-wall cuts off/pinches inward to form a conidium
Describe thallic conidiogenesis
a cell wall develops and forms a barrier (cross-wall) to produce conidia at the hyphal tip
this occurs before differentiation of conidium occurs
What is dehiscence? what are the 2 types?
the process by which a mature conidium is released (anamorphs)
schizolytic
rhexolytic
Describe schizolytic dehiscence
a new septum forms to separate the 2 cell compartments and pinches off at the septum (think like a vesicle pinching off a membrane) to release the conidium
in anamorphs
Describe rhexolytic dehiscence
the outer cell wall between conidia breaks apart and detaches to release the apical conidium
in anamorphs
How many types of conidiogenesis are known?
> 9 blastic
3 thallic
What are the 4 basic arrangements/aggregations of conidiophores? describe them
simple - simple modified hyphae that produce conidia at the tip
complex - single modified hyphae with multiple branches that each have multiple conidia at the tip
synnematal - multiple conidiophores are aligned in a column and each produces conidia
sporodochial - multiple conidiophores are bundled in close proximity (look like a cushion) to form a mass of hyphae that produce conidia
Give an example of each type of conidiophore aggregation
simple - Aspergillus sp.
complex - Penicillium sp.
synnematal - Graphium sp.
sporodochial - Tubercularia sp.
Describe dimorphism
when a fungus can exist and grow as either a single-celled yeast morphology or as a filamentous, mycelial morphology
Which growth morphology (yeast or mycelial) is typical of most fungi? which lifestyles typically use dimorphic strategies?
mycelial
commonly found in plant and animal pathogens
What dictates the growth morphology?
environmental and physiological conditions
genetic status
What are the benefits of dimorphism (transition from mycelium to yeast) for the fungus?
supports host infection (mycelium is easier to locate and penetrate host) and growth/spread within host (yeast easier to replicate and move around host body)
movement inside animal and plant systems
increases stress tolerance - smaller size and shape
easier to avoid host detection and cause immunoresponses
yeasts require less resources than mycelia
What are 2 triggers for switching from mycelium to yeast morphology?
temperature change (thermal dimorphism)
change caused by penetrating the host’s tissues
Give an example of a mammalian, plant and insect pathogen species that exhibits dimorphism
mammal: penicillium marneffei (penicilliosis)
plant: Ophiostoma ulmi (Dutch elm disease)
insect: Ophiocordyceps unilateralis (‘zombie ant’)
T or F: dimorphism is only commonly observed in Ascomycetes
false, also observed in Basidiomycetes
What are truffles?
the fruiting body of some Ascomycetes that grows underground (hypogeous)
What lifestyles do truffles exhibit?
ectomycorrhizal with some trees - ex. hazelnuts, oaks
How are truffles dispersed?
animal vectors (ex. boars)
What organisms (symbionts) are required for a truffle life cycle?
truffles require an ectomycorrhizal association with specific trees (ex. hazelnuts) and an animal vector (ex. boars) for dispersal
How do animals locate truffles if they grow underground?
truffles release aromas which can be smelled by animals when spres are mature
When do truffles mature?
Feb-Marchc
How do truffles grow in deserts?
by forming mycorrhizal associations with shrubs (ex. Tirmania nivea)
What are some examples of important culinary truffles?
Perigord Mediterranean black truffles (Tuber melanosporum)
Summer/burgundy truffle (Tuber aestivum) Mediterranean
Smooth black truffle Tuber macrosporum
Italian white truffles: Tuber magnatum, Tuber borchii (bianchetto)
Tuber lyonii (pecan truffle) - eastern NA
Tuber canaliculatum (Appalachian) - Quebec
Tuber indicum (Chinese black truffles)
What are examples of non-culinary truffles found in BC?
Thaxterogaster pingue
Chamonixia caespitosa
Rhizopogon vinicolor
What are examples of culinary truffles found in BC? which plant do they form ECM with? have any been cultivated?
Leucangium carthusianum - western black truffle
Tuber gibbosum - spring western white
Tuber oregonense - winter western white
all associated with douglas-firs
none have been cultivated yet
What are some examples of truffle pests and diseases?
Eastern filbert blight on hazelnut trees
truffle rot
slugs
What are some current challenges to cultivating truffles in BC?
high demand and competition for mycorrhizal host species against native ECMs in BC - they require a high pH to keep out native ECMs
Some species mature during winter and if the ground freezes, the truffles will rot when ground thaws
a long time commitment (5-15 yrs before first truffle growth)
expensive!! have to be very cautious with nurseries and inoculated spores to ensure correct species
need the right ECM plant hosts
need trained dogs to harvest
need pest/disease management for host species
short shelf-life
Weigh the pros and cons of innoculated truffle spores for cultivation vs. growing truffle cultures?
innoculated spores are more expensive to purchase but better for genetic diversity
culturing produces clones
