Plant Path Quiz #4

Ascomycota

• Asci sac-like sporangia with 8 sexual spores inside

• sexual spores are called ascospores

• can also make asexual spores

• most have septate hyphae

• ascus singular term

• may have two different scientific names

Basidiomycota

• basidia club-shaped sporangia holding four sexual spores

• sexual spores are called basidiospores

• they also contain structures on the hyphae called clamp connections

• basidium singular term

Ascomycetes produce…

a sack-like ascus (pl. asci) that contains eight ascospores

• Ascospores are produced by meiosis and are each 1n

Ascomycete lifecycle

Ascomycete lifecycle includes both sexual and asexual cycles and the haploid (n) stage dominates.

Ascocarps

sexual reproductive structures of ascomycetes, including cleistothecia (chasmothecia), perithecia, and apothecia

Cleistothecia (chasmothecia)

A closed, globose fruiting structures containing asci inside.

Perithecia

Pear-shaped fruiting bodies with asci inside

Apothecia

Small cup-shaped fruiting bodies made up of tightly woven hyphae and asci.

Conidiophores

Conidiophores are aerial hyphae that produce conidia, the asexual spores of ascomycetes.

• Conidia: 1n haploid spores produced by mitotic cell division

Basidiomycota lifecycle has a dominant…

dikaryotic stage and does not include an asexual cycle.

Basidiomycete clamp connections

needed for each cell to be bi-nucleate as the hyphae elongate.

All vegetative hyphae and visible structures are…

dikaryotic (n+n) and sexual recombination occurs in the gills

Hyphal fusion forms…

dikaryotic hyphae, followed by nuclear fusion and meiosis to form haploid basidiospores.

Anamorph

The asexual reproductive form in the life cycle of any fungus, whereas the teleomorph is the sexual reproductive form in the life cycle

Because some fungi have two forms that were discovered at
different times, they have an ________ name

anamorphic and teleomorphic

Fusarium graminearum is the ________ and Gibberella zeae
is the ________

Fusarium graminearum is the anamorph and Gibberella zeae
is the teleomorph

Ascomycota are predominantly ________ and can undergo ________, whereas Basidiomycota have a long ________

Ascomycota are predominantly haploid and can undergo asexual
reproduction, whereas Basidiomycota have a long dikaryotic phase

Fusarium

• Ascomycota

• Fusarium is a large genus of filamentous fungi, widely distributed in soil and associated with plants

Many Fusarium species produce ________

• mycotoxins, which are any toxic substance produce by a fungus

• These chemicals may operate in nature to disable plant defense mechanisms or to defend the fungus against other microorganisms

Mycotoxins

Only produced by certain fungi and under specific conditions (temperature and moisture).

Cryptic species

Cryptic species are species that are difficult to distinguish based on morphology but can be identified by their DNA sequences and sometimes hosts

• often make up a species complex: a group of closely related organisms
  that are so similar in appearance and other features that it’s hard to distinguish them apart.

The term “Forma specialis” denotes…

taxonomic groups with a specialized host (range) within a fungal species

A race is defined as…

a population (within a species) of which all individuals carry the same combination of virulence gene

Fusarium head blight (FHB)

• Caused by Fusarium graminearum is an important disease globally, and produces a mycotoxin

• FHB occurs in small grains (wheat, barley, and oats) and corn

• F. graminearum (anamorph) only produces macroconidia

• Gibberella Zeae (telemorph) produces ascospores

• Hemi-biotroph

Deoxynivalenol (DON)

Has stringent allowable concentrations in food for humans and animals

DON

Disrupts normal cell function by inhibiting protein synthesis and will cause symptoms of nausea, fever, headaches, and vomiting

FHB

FHB inoculum includes macroconidia (clustered together to form
sporodochia) and ascospores produced in perithecia

Symptoms of FHB

premature bleaching of the cereal head (ear) and shriveled and discolored kernels

Fungi that are heterothallic require

A compatible partner for sexual reproduction, but homothallic fungi are self-fertile and can
sexually reproduce without a partner

Most of the isolates of F. graminearum are…

Homothallic, meaning they are self-fertile and can sexually reproduce without a partner

FHB Management practices

preventative fungicide application, using partially resistant cereal varieties, biological
controls, cultural practices like crop rotation, and RNAi

FHB is well suited for disease forecasting because…

Its narrow time periods of pathogen sporulation, spore dispersal, and host infection that contribute to epidemic development

Rice blast

Caused by Magnaporthe oryzae is a devastating disease of rice

• Annual 30% global loss,equivalent to 60 million people.

• M. oryzae has a broad host range in Poaceae, but individual isolates are host-
  limited.

• Hemi-biotroph

Rice blast disease cycle

Rice blast steps to infection

Steps to infection: Adhesion of conidium to plant cell using mucilage

• The conidium germinates and starts to form an appressorium
  based on chemotaxes of cutin extracts

• The appressorium has a melanin layer that enables it to build
  up immense turgor pressor, leading to the penetration peg,
  which punctures through the plant cell wall

• The fungus secretes molecules that
  inhibit plant detection and defense in
  the biotrophic stage, and then toxins
  during the necrotrophic stage

Rice blast management

Rice blast management includes destroying infested crop
residue before and during the growth cycle, planting resistant
or tolerant varieties, and applying a preventative fungicide

Verticillium wilt (Verticillium dahliae)

Colonizes the xylem of many plant hosts

• Causes disease on over 300 plant species

• Nightshade family (solanaceous plants), cucurbits, mint, and strawberry

• Initial symptom is yellowing of bottom leaves, v-shaped lesions, wilting,
  and discoloration of the vascular tissue and tubers (potatoes)

• Hemi-biotroph

Verticillium disease cycle

Management practices for verticillium wilt

Management practices for verticillium wilt include sanitation, managing weeds that could be alternative hosts, managing the soil (e.g., solarization), and crop rotation with grasses

Sclerotinia sclerotiorum

a ubiquitous necrotroph globally

• Causes disease on over 400 plant species except for grasses

• Bleaching and lodging (falling over) of plants

• White fluffy mycelium and black rock-like sclerotia

• Sclerotia are the primary sources of inoculum and can either germinate into ascocarps which produce ascospores or hyphae

Stemphylium leaf blight

(Stemphylium vesicarium) is a re-emergent disease of onions

Taphrina spp.

biotrophic and have naked asci

Disease cycle of peach leaf curl (T. deformans) and plum pocket (T. communis)

Monilinia vaccinii-corymbosi

is a biotroph that attracts insect vectors via floral mimicry

• Pollinators are tricked into landing on infected leaves by their
  change in color and composition of volatile organic compounds

Pseudoflowers

Form in yellow-eyed grass infected with Fusarium xyrophilum