Studied by 8 people
disease lessons, chestnut blight, mitosporic fungi, basidiomycetes (rusts and smuts) , rust fungi, smuts, soil-borne fungal diseases, bacterial disease
chryphnoctria parasitica
causual agent of chestnut blight
what does chestnut blight have in common with dutch elm disease?
both pathogens are exotic; came out of asia
they decimated iconic tree species (american chestnut, american elm)
both are ascomycetes
how does cyrophenctria parasitica reproduce sexually and asexually?
produce asexual conidia in a pycnidium
produce sexual ascospores in a perithecium
pycnidium
flask-shaped asexual fruiting body
perithecium
flash-shaped sexual fruiting body containing asci and ascospores
what sort of symptoms/signs does chestnut blight show?
large cankers at the base of the stem
these cankers can be a meter in length
girdling stem at the base, which means if the tree dies, the roots stay alive and produce new shoots
extent of tree death caused by chestnut blight
killed 4 billion american chestnuts
lowered the timber value in the eastern us by 15%
they were replaced by oaks, which are now dominant in hardwood forests because of the disappearance of chestnuts
why was there so much tree death in chestnuts?
the american chestnut had never encountered this pathogen before, so it did not have the ability to fight it off or develop resistance against the pathogen, which is what made it so devastating
similar to COVID-19 hitting human population
when was cryphonectria parasitica introduce to the US?
1904
an exotic chestnut was introduced into the bronx botanical garden, which introduced the pathogen
killed 4 billion chestnuts
no host resistance in the american chestnut
what can be done about the devastation of chestnut blight?
hybridization, biological control, or transgenic control
are all control efforts 100% successful?
no, these are mostly attempts to control
hybridization
attempt with asian chestnuts, which are resistant
species that are native to asia have host resistance, so hybridization could make american chestnuts more resistant
there still needs to be more research
biological control
looks promising in europe, but not so much the US
control with mycovirus
mycovirus
viruses that can affect fungi;bacteria
attacks fungi and causes hypovirulence
when you infect a pathogen with a virus, they become sick
disease is being reduce because of the reduction in growth
however, viruses are hard to transmit
how are mycoviruses administered?
inoculate the strain with the virus into the canker and it makes the pathogen hypovirulent
hypovirulence
lowering relative ability to cause disease
transgenic chestnuts
genetically modified chestnuts with the oxalate oxidase (enzyme) gene from wheat
it moves the gene from one species to another (wheat to chestnut)
it breaks down the oxalate so the host is able to suppress the pathogenicity factor
this permits resistance to the disease
chestnut blight
pathogenic fungus Cyrophonectria parasitica
member of the ascomycota (sac fung) it’s an ascomycete
necrotrophic fungus native to east asia and south east asia
introduced to europe and north american in early 1900s
spread rapidly and caused tree loss
how does the pathogen in chestnut blight persist?
windborne ascospores and conidia distributed by rainsplash
what are the signs/symptoms of chestnut blight?
fungus enters through wounds on susceptible trees and grows under the bark, killing the cambium all the way around twig, branch or trunk
first symptom is small orange-brown area on bark
sunken canker forms as the mycelial fan spreads under the bark
they produce toxic compounds (oxalic acid) and it reduces the pH of infected issue, which is toxic to plant cells
canker girgles the tree, killing everything above it
distinct yellow conidia tendrils can be seen in wet weather
what type of parasite is cryphonectria parasitica?
obligate parasite
obligate parasite
only survive on living host
dutch elm disease
ophiostoma ulmi or ophiostoma novo-ulmi (north america and europe)
where was dutch elm disease first identified?
netherlands in 1921
what elm species is particularly susceptible to dutch elm disease?
Ulmus americana
what are the symptoms and signs of dutch elm disease?
vascular wilt disease
earliest external symptoms of infection are the yellowing and wilting (flagging) of leaves on individual branches
these leaves turn brown and curl up as the branches die, and the leaves may drop
initially only a party of the tree crown may be affected
symptoms may progress rapidly throughout the crown
highly susceptible trees usually die in a year, but some linger for years
when do symptoms progress the quickest in dutch elm disease? why?
symptoms progress quickly and death happens quickly in trees infected in early spring
trees infected later in the summer may survive longer
explain symptoms and signs of the bark caused by dutch elm disease
if the bark of infected elm twigs or branches is peeled back, brown discoloration is seed on outer layer of wood
discoloration in xylem occurs before foliar symptoms
xylem browning is discontinuous
what do you see in the xylem browning of dutch elm disease?
discontinuous
cross section shows circle of brown dots or a ring
why do you need labratory culturing and identification of the dutch elm fungus?
other wilt diseases of elm (Verticillium wilt) also cause sapwood discoloration so you need lab culturing and ID of fungus to identify which disease it is
why do foliar symptoms result?
sap flow ceases in the infected wood
where are the signs of dutch elm disease?
fungal structures of the pathogens are found within infected elm trees
explain the pathogen biology of dutch elm disease
Ophiostoma species that cause Dutch elm disease grow and reproduce only within elms
they’re facultative saprophytes
Ophiostoma ulmi caused the original Dutch elm disease epidemic in europe and north america in the mid 1900s
Ophiostoma novo-ulmi, even more aggressive, replaced former pathogen
ophiostoma sp. pathogen
fungi spread within stems and roots of living elms both by passive transport of spores and by mycelial growth of colonies initiated by spores that germinate in the xylem
mycelium is creamy whit
composed of septate hyphae with haploid nuclei
where do the spores of ophiostoma germinate?
the xylem
what color is the mycelium of ophiostoma?
creamy white, septate hyphae with haploid nuclei
asexual reproduction of ophiostoma ulmi and O. novo-ulmi
two asexual forms that produce asexual spores called conidia
in the xylem vessels of living elm trees, small, white, oval conidia are formed in clusers on short mycelial brances
the conidia are carried in xylem vessels where they reproduce by budding, germinate to produce mycelium, and thus spread the disease throughout the tree
how are conidia in ophiostoma sp. produced?
in dying or recently dead trees, conidia are produced by mycelium growing in the bark and in tunnels created by beetles just under the bark
they’re produced at the tip of 1-2mm tall synnemata
explain the synnema of ophiostoma sp.
each synnema consists of hyphae fused to form an erect, dark stalk with a round, nearly colorless head of sticky spores
beetle vectors cary the stick spores to new elm trees
synnema
stalk (dutch elm disease)
sticky conidia on the stalk, beetles carry it around
explain the sexual reproduction of ophiostoma sp.
based on sexual stage structure, this pathogen is an ascomycete genus Ophiostoma
when two mating types come in contact, ascospores are produced in sperical, black, long-necked perithecia
perithecia form in the bark, either singly or in groups.
ascospores are produced in the asci that degenerate inside of the perithecia
free ascospores are discharged at the opening of the perithecial neck where they accumulate in sticky droplets that may be disseminated by beetle vectors
disease cycle and epidemiology of dutch elm disease
pathogens overwinter in the bark and outer wood of dying or recently dead elm trees and in elm logs as mycelia and synnemata with conidia
fungi are spread from their sites by their vectors (elm bark beetles)
two beetle species spread the pathogens in North America: Scolytus multistriatus and Hylurgopinus rufipes
what are the two beetles species that can spread the pathogens around in north America? how do they act as vectors for ophiostoma sp.?
smaller European elm bark beetle: Scolytus multistriatus
native elm bark beetle: Hylurgopinus rufipes
adult female bores through the bark of dead or dying elm trees and elm logs and creates a tunnel in the wood as she feeds
she lays eggs in the tunnel behind her
the eggs hatch into larvae that being to feed, creating tunnels at right angles to the maternal tunnel
what is the resulting pattern of tunnels created by elm bark beetles called?
it’s called a gallery
larvae pupate and emerge through the bark as adultsif fungi are present in the tree or log, emerging adults carry thousands of sticky conidia on their bodies
how do newly emerged bark beetles feed?
S. multristriatus adults feed in the twig crotches of elm branches
H. rufipes adults tunnel in the bark of the elm branches and trunks
how are fungal spores spread by elm bark beetles?
as beetles feed, fungal spores are deposited
beetle vectors only feed on healthy elms for a few days
then they fly to dying or recently dead elm trees or to freshly cut elm wood to feed, create galleries, and lay eggs
the spores dislodged from the elm bark beetles in feeding wounds and tunnels germinate and produce mycelium that grows into the xylem the mycelium produces millions of small, white, oval conidia that spread through the xylem sap (vascular disease)
does the fungi produce toxins (ophiostoma)?
yes, they produce enzymes and toxins that degrade plant cell walls and kill xylem parenchyma cells
they also induce hormonal imbalance that leads to the development of tyloses overgrowths of parenchyma cells that push into and block the water-conduction xylem cells
blockage of the xylem by tyloses and gums (thought to be products of plant cell wall breakdown) causes wilting leaves
killing of xylem parenchyma cells also causes brown discoloration just under the bark
epidemiology of the dutch elm disease
infections that take place in spring or early summer involve springwood which has very long xylem vessels
this makes it easier for fungi to spread rapidly throughout the tree, which will then die very quickly
later in the season, the fungi are restricted to shorter vessels of summerwood
fungi spread slowly in the tree
what kind of infections result in the elm tree surviving for longer? (Ophiostoma sp.)
localized infections result because of summerwood and later summer season infections, and the tree survives for longer
how do healthy elm treeds being infected by the dutch elm disease?
they can become infected by the feeding spore-contaminated elm bark beetles or through the development of grafts between their roots and the roots of infected trees
trees infected by beetle vectors develop dymptoms first in an upper section of the crown
trees graft infected via root grafts first develop symptoms in the lower crown
how does infection by root grafts in elm trees function?
when fungi are introduced through root graft, they distribute quicker throughout the tree in the vascular system and the entire tree can wilt and die
root grafts form naturally bewtween closely spaced elm trees with intertwined roots
large elms growing within 20 feet of each other have a 100% chance of root graft infection
likelihood of spread is lower when they’re at least 40 feet apart
what does the severity and rate of spread of dutch elm disease depend on?
species of pathogen
how rapidly elm bark beetles reproduce
level of susceptibility of elm hosts
environment
temperature around 68 F favor formation of conidia
perithecia are induced at 46 to 50 F
what is the ideal temperature for ophiostoma sp.
68F favors conidia formation
46-50F favors perithecia induction
what are the three similarities between dutch elm disease and chestnut blight?
both exotic pathogens (Asia)
both decimated popular tree species (american chestnut and american elm)
both ascomycetes
what happens to elm population impacted by ophiostoma sp.
without effective management, dutch elm disease increases exponentially until an affected elm population is greatly depleted
seedlings and saplings can escape and live long enough to reproduce, so even the most susceptible elm species have never been threatened by extinction
wild elm populations have increased in easter and midwestern US, leading to renewed prominence of dutch elm disease in landscapes
what are the three different types of dutch elm management?
cultural strategies
chemical strategies
breeding for resistance (transgenics)
what are the cultural strategies for managing dutch elm disease?
it’s cheapter to manage the disease than to remove the large dead trees that it leaves behind
some communities focus on cultural practices for disease management, including avoiding monocultures of elm trees, removal of all dying or recently dead branches, trees, and cut wood (sanitaton) and the breakage of root grafts between adjacent elms
success depends on diligent insepction of all elm trees in area several times each growing season
wood must be burned, chipped, or buried so it can’t provide a home for beetle vectors
what is organized community sanitation for dutch elm disease?
can delay the loss of elms
the time when half of the elm trees in an area have been lost can be delayed between 7 to 30 years
if privately owned trees are included in inspection and mandatory removal, the longer end of this range is likely
this is mostly a delaying tactic (burn wood)
what are chemical strategies for managing dutch elm disease?
in the past, insecticides were sprayed on elm trees in attempts to kill the beetle vectors of dutch elm disease
management strategy was expensive and not effective, and people attacked it because of concern about wildlife and people
fungicides are relatively expensive, non are completely effective
chemical management is used only to protect elm trees of high value (DC Mall, well-maintained properties)
breeding for resistance to fight ophiostoma sp.
long term solution
development of disease-resistant cultivars of elms
several asian elm species have moderate to high resistance
breeding programs introduced resistance from asian elm species to native elm speces
american elm breeders want to maintain the shape of the american elm, which is what makes it a desirable shade tree
several hybrid and clonal elms are available that have good resistance to dutch elm disease
historical signification of ophiostoma sp.
first elm disease epidemic started when it was introduced in 1920s by furniture makers
used imported European elm logs to make veneer for cabinets and tables
some of the beetle vectors were brought from Europe years before the fungi were introduced
when more aggressive O. novo-ulmi was later introduced to America, it killed many elms that survived the original epidemic
the spread of this disease highlights the danger of moving plant materials around the world
who first identified the causal agent of the dutch elm disease?
dutch scientist, Marie Beatrice Schwarz
who first identified dutch elm disease in ohio in 1930?
dutch scientist, Chrstine Johanna Buisman (she had seen the disease in her homeland) first identified it in ohio in 1930
how did ophoistoma geographically spread?
spread up and down the east cost and west across the contient
reached west coast in 1973
over 40 million american elm trees have been killed by this disease, and today it is still a very destructive disease of shade tree
impact of elm monocultures
they were planted in rows along streets and walkways
provided effective windbreaks
shady canopies
dense plantings are monocultures
monocultures
when plants of the same species are grown in close proximity with few other types of plants prsent
people have planted these for hundreds of years
provide uniformity
aesthetic and production practices
planting, management, and harvest are simpler when one kind of plant is grown in an area
dangers of monocultures
they’re subject to the same catastrophic problems because they’re the same species
disease, insect, or weather condition that harms one plant harms the rest too
this is what made dutch elm disease so devastating in towns and cities
pathogens can move closely between closely spaced trees through insect vectors or root grafts, leaving destruction
this highlights why diversity is important
explain transgenics in american chestnuts
American chestnut is engineered to express wheat oxilate oxidase. This enzyme degrades the oxalate produced by the pathogen, resistance of Cryphonectria parasitica
oxalate oxidase enzyme
this enzyme converts oxalic acid into hydrogen peroxide and carbon dioxide
when the fungus attempts to penetrate the chestnut, the oxalic acid produced by the fungus is broken down by the enzyme, creating hydrogen peroxide
hydrogen peroxide is toxic to the fungus
this kills the fungus
what are the ascomycetes we discussed in class?
powdery mildews, apple scab, dutch elm disease, chestnut blight, block spot of rose
deuteromycetes
aka anamorphic
fungi with no known sexual stage
they only have asexual reproduction
deuteromycetes and ascomycetes
includes many species causing leaf/fruit spots, blights, cankers, root rots, vascular wilts, anthracnose, also powdery mildews
deuteromycetes are imperfect, ascomycetes are perfect fungi
both eukaryotic species
ascomycetes
both sexual and asexual reproduction
sac fungi
largest phylum of the kingdom fungi
ascus - sexual structure that produces ascospores, some produce asexual only
deuteromycetes are considered the anamorphic stages of ascomycetes, they produce spores asexually through sporogenesis
one fungus one name
many fungi, especially ascomycetes used to have 2 scientific names (sexual and asexual) (telemorph and anamorph respectively)
since 2013, only ONE name (holomorph) is applied
cell wall composition of mitosporic fungi
made of chitin and not cellulose
examples of mitosporic fungi
Alternaria
Botrytis
Colletotrichum
Fusarium
Pythium
asexual spore types
always conidia
conidia
nonmotile, germinate directly
four asexual fruiting bodies
pycnidium, acervulus, sporodocnium, synnema
pycnidium
flask shaped
chestnut blight
acervulus
subepidermal saucer, anthracnose
sporodochium
cushion
peach brown rot
synnema
stalk
dutch elm disease
chlamydospores, sclerotia
both are survival structures
chlamydospores
thick-walled resting structures produced by some fungi that allow them to survive unfavorable conditions
thickening and hardening of fungal cell wall, provides protection
asexual spores
source of inoculum
can remain dormant for extended period untl conditions are right to germinate
sclerotia
compact, hardened structures that are formed by fungi for survival
hyphal tissue that has become compacted and encased in a thick, protective layer
four main groups of basidiospores
no spores
athelia rolfsii
rhizoctonia solani
produce only basidiospores
Armillaria mellea, oak root rot
basidiospores and teliospores
smuts
ustilago nuda, ustilago maydis
basidiospores, teliospores, and up to three more spore stages
rust fungi
puccinia graminis f sp tritici
stem rust of wheat
what is the sexual spore of basidiomycetes and what are they produced on?
basidiospores produced on basidia
nuclear condition of basidiomycetes
haploid spores
plasmogamy takes place; makes it infective
two basidiospores land on same area, germinate, form germ tube
forms dikaryotic mycelium
karyogamy occuers when two haploid nuclei fuse to form diploid nucleus, meiosis occurs in the basidium to produce four haploid basidiospores
obligate parasite
require a living host to survive
forma specialis vs physiological race
different races of rust fungi can cause different symptoms, wide host range
physiological races often have names
forma specialis is strain of fungus that is specialized in terms of its virulence (it can overcome certain resistance genes in a host)
distinct form that only infects specific host/group related to hosts
autoecious vs heterocious
autoecious
one host life cycle
heteroecious
two or more hosts needed to complete life cycle
primary host: basidiospores form
secondary host
microcylic vs macrocylic
microcylic
two spore stages: basidiospores and teliospores
macrocyclic
up to five spore stages
primary host
survival
produced in telium
on primary host, survival spore
thick-walled
telium: postule that produces all these spores (black postules in stem wheat rust)
germinate to produce a basidium from which the sexual basidiospores are formed
karyogamy happens in teliospore (diploid)
basidiospores
genetic recombination
infect secondary host
produced on basidium
meiosis happens in basidiospores
secondary host
spermatia
plasmogamy
produced in spermagonium = pycnium
pycniospores
aeciospores
infect primary host
produced after fusion between pycniospores
goes back to infect the primary host in the spring/summer
produced in aecium
uredospores/ urediniospores
multiple sporulation
re-infect same host
produced in uredium
repeating spore stage
what are the five spore stages and fruiting structures of macrocylic rust? What is function of each spore type?
spore stage teliospores
survival
produced in telium
on primary host, survival spore
thick-walled
telium: postule that produces all these spores (black postules in stem wheat rust)
germinate to produce a basidium from which the sexual basidiospores are formed
karyogamy happened in teliospore (diploid)
basidiospores
genetic recombination
infect secondary host
produced on basidium
meiosis happened in basidiospores
secondary host
spermatia
plasmogamy
produced in spermogonium = pycnium
pycniospores
aeciospores
infect primary host
produced after fusion between pycniospores
goes back to infect the primary host in the spring/summer
produce in aecium
uredospores/urediniospores
multiple sporulation
re-infect same host
produced in uredium
repeating spore stage
name a rust fungus with four spore stages and where the different spore types are produced
cedar apple rust
cedar-quince rust
they have four spore stages:
basidiospore, spermatia, aeciospore, and urediniospore
basidiospores are produced on cedar tree
infects apple or quince trees
spermatia and aeciospores are produced on apple or quince tree
infects cedar tree
urediniospores are produced on the apple or quince tree and cause typical rust symptoms
what are the two spore types produced in smuts?
teliospores and basidiospores
what are the three major types of smuts and what are the symptoms of each?
covered smuts
loose smuts
flag smuts
covered smuts
formation of black, spore-filled structures on the surface of infected plant part
heads of cereals
can survive in soil or on seeds and infect plant during germination
loose smuts
absence of inflorescence
flowers develop directly into black, powdery masses of spores
survive in soil or on seeds and infect during germination
flag smuts
formation of spore masses in the axils of leaves or the flag leaf, resulting in distortion and breaking of leaves
overwinter as mycelia in plant debris and infect the plant during the next growing season
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