Exam #2 - Ch.2, Plant Diseases Caused by FUNGI (21-27)

Fungi can be:

a. saprophytes

b. biotrophs

c. necrotrophs

all of them

____ refers to an individual filament, while the term ____ refers to the body of the fungus (collectively all of the filaments)

hypha; mycelium

The study of fungi

Mycology

Why do some symptoms caused by fungi generally have a circular shape?

because the mycelium grows radially outward from a central point, which naturally forms a circle

T/F

Most structures of plant pathogenic fungi tend to be macroscopic, easily seen without a microscope

False

Fungi are autotrophic / heterotrophic organisms

heterotrophic

Fungi — cell types are: Eukaryotic / Prokaryotic

Eukaryotic

Fungi — adult cells tend be diploid / haploid

haploid

Fungi:

a. Cell wall made of cellulose

b. Cell wall made of chitin

c. Cell wall made of glycogen

d. Lacks cell wall

b. Cell wall made of chitin

Fungi store carbs in the form of glycogen / starch

glycogen

Fungi — cells and organisms tend to be motile / nonmotile

nonmotile

What are the other terms for Nonseptate hyphae?

Aseptate and Coenocytic

Define Nonseptate

hyphae without cross walls

Which fungal group(s) does Nonseptate apply to?

Oomycetes and Zygomycetes

Define Septate

hyphae with cross-walls

Which fungal group(s) does Septate apply to?

Ascomycetes and Basidiomycetes

How could knowledge of the type of hyphae (septate v. nonseptate) be useful for disease diagnosis?

it is going to help narrow down/determine which major group the fungus belongs to

The “hump” on hyphae, above the septum, is called?

clamp connection

If you see hyphae with a clamp connection, you know the fungus belongs to which group?

basidiomycetes

What is the function of Haustoria?

nutrient absorption

In fungi, haustoria are formed from modified ___

hyphae

What is the difference between Intercellular and Intracellular hyphae?

Intercellular → between or among cells

Intracellular → through or within cells

What is a spore?

reproductive units of fungi

What role(s) do spores have in the disease cycle and why?

They help the pathogen survive, disperse, and act as an inoculum to initiate new infections in the disease cycle

Fungal spores are different / similar in size and shape

different

Sexual reproduction involved which two essential events/processes?

meiosis and syngamy

Define Syngamy

the process of two haploid cells fusing to become one diploid cell

The process of Syngamy is subdivided into which two stages?

plasmogamy and karyogamy

Define Plasmogamy

fusion of cells, bringing two sexually compatible haploid nuclei together in one cell

(the fusion of two sex cells)

Define Karyogamy

nuclear fusion, forming a diploid nucleus

(the fusion of nuclei)

Define Meiosis

formation of four genetically recombined haploid nuclei from a single diploid nucleus

What is the difference between a cell that is N+N and a cell that is 2N?

N+N → 2 haploid nuclei in 1 cell (not fused)

2N → 1 diploid nucleus (fused)

What allows fungi to readily adapt to “easily” become resistant to fungicides and overcome host resistance genes?

sexual reproduction because it provides genetic diversity for the continued ability of the species to adapt to changing conditions

What is a fruiting body (fruitbody)?

a mass of hyphae that produces (inside or on the surface) and protects spores.

Why are fruiting bodies (fruitbody) important for fungi?

the thickened cell walls help prevent moisture loss (desiccation).

the cell walls may contain melanin, which provides protection from UV radiation.

Asexual / Sexual spores tend to be mainly involved in dormancy

Sexual

Asexual / Sexual spores tend to be mainly involved in dispersal and causing secondary infection

Asexual

List unique aspects about Armillaria spp. (cause root rots of trees)

1. weight of Armillaria gallica mycelium (110 tons)

2. age of Armillaria ostoyae (2400)

3. ground covered by Armillaria ostoyae (2200 acres)

T/F

Scientists have found and identified (named) all species of fungi that exist

false

How many different diseases caused by fungi (aka ‘unique fungus-host combinations’) are known to occur within the US?

78,000

T/F

All fungal pathogens cause the same kinds of symptoms, and the symptoms are the same on each part of a host plant

false

Symptom - Circular Spots

→ Describe how a fungus could cause this symptom

the fungus grows radially from a central starting point

Symptom - Canker

→ Describe how a fungus could cause this symptom

fungi invade phloem and vascular cambium, causing sunken areas on stems and twigs

Symptom - Vascular Wilt

→ Describe how a fungus could cause this symptom

fungi invade the xylem, impeding water transport, leading to wilt and discoloration of the active xylem

Symptom - Stunting + Wilt

→ Describe how a fungus could cause this symptom

fungi cause this when they also cause root rot - plant will have symptoms of nutrient deficiency, and their roots may be brown and deteriorated

Why is it important to also find signs of fungi, and not merely rely on symptoms seen?

because many of the possible symptoms can also be caused by other kinds of pathogens

List some possible signs of fungal pathogens

mycelium, hyphae, spores, fruiting bodies

Fungi that reproduce sexually and asexually often have what # of scientific or Latin names?

two (or more)

The ____ name refers to the sexual stage

teleomorph

The ____ name refers to the asexual stage

anamorph

What is the holomorph?

the whole fungus in all its stages, sexual and asexual

Many plant diseases are caused by the asexual / both sexual and asexual / sexual stages of fungi

asexual

What are imperfect fungi?

group of fungi without the sexual stage - they either lack the sexual stage, or it has not yet been found

T/F

It is nearly impossible to identify fungi by their mycelium alone; one must look at spores and/or fruitbodies for positive ID

true

The true fungi are placed into Kingdom Fungi, and these four phyla or groups belong there:

Ascomycota, Basidiomycota, Chytridiomycota, Zygomycota

Other fungal-like pathogens are placed into the Kingdom Protista (and are sometimes called fungal-like protists).

Why are these organisms considered ‘fungal-like’ (why are they included in the fungus chapter)?

They are similar in the kinds of plant diseases they cause and in how those diseases are managed. Many have adaptation for dispersal, infection, and survival, similar to true fungi.