Mycotoxins and Fungi Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

Which mycotoxin is known to cause equine eucoencephalomalacia (ELEM)?

Aflatoxin B1

Ochratoxin A

Fumonisin B1 (correct)

Deoxynivalenol (DON)

Which of the following symptoms may be caused by aflatoxin exposure in animals?

Respiratory distress

Skin lesions

Nervous system disorders

Poor growth (correct)

What is the primary method used to detect Fusarium species in Ireland?

Visual inspection

RNA sequencing

DNA-based detection (correct)

Chemical assays

Which environmental factors can influence the growth of mycotoxin-producing fungi?

Temperature and humidity Signup and view all the answers

Which mycotoxin has been suspected as a human carcinogen by IARC?

Ochratoxin A Signup and view all the answers

What is the adverse effect attributed to deoxynivalenol (DON)?

Inhibition of protein synthesis Signup and view all the answers

Which crop is most commonly associated with ochratoxin A contamination?

Barley Signup and view all the answers

Which of the following fungi is known for producing aflatoxins?

Aspergillus flavus Signup and view all the answers

What is the main cause of seedling blight in cereal crops?

Fungal infections primarily from soil Signup and view all the answers

Which of the following symptoms is NOT associated with seedling blight?

Increased germination success Signup and view all the answers

Which fungus is primarily responsible for causing seedling blight within the Fusarium group?

Microdochium nivale Signup and view all the answers

What does legislation typically impose regarding mycotoxins in grain?

A limit on certain mycotoxin levels Signup and view all the answers

What type of conditions can lead to increased risk of Fusarium ear blight?

Wet conditions during flowering Signup and view all the answers

Which of these fungi is NOT typically involved in soil-borne infections leading to seedling death?

Aspergillus spp. Signup and view all the answers

What is a common outcome for seedlings that are affected by seedling blight?

They may emerge but then become stunted and die. Signup and view all the answers

Which management practice is crucial for preventing Fusarium seed-borne infections?

Seed treatment to control pathogens Signup and view all the answers

What is the recommended action if 20% or more of the tillers are affected by eyespot at GS 30/31?

Begin eyespot control measures Signup and view all the answers

Which fungus type is currently the dominant species responsible for eyespot infections?

R-type Signup and view all the answers

What environmental conditions are necessary for the infection of crops by the eyespot fungus?

Wet weather with temperatures above 5°C Signup and view all the answers

What is a serious consequence of severe eyespot in crops?

Lodging of the stems Signup and view all the answers

How long can the eyespot fungus survive on stubble?

3 years Signup and view all the answers

Which crops are considered at greatest risk for eyespot infection?

Winter wheat, winter barley, and spring wheat Signup and view all the answers

What stage of the eyespot fungus's life cycle produces ascospores that can infect young plants?

Sexual stage Signup and view all the answers

What factor increases the risk of eyespot infection in crops?

Early sowing combined with wet weather Signup and view all the answers

Study Notes

Fungal Diseases - Foot and Root Rots

These diseases affect foot and root systems of crops.
Dr. Josephine Brennan, Department of Agriculture, Fisheries & Food, Celbridge, Kildare, presented these notes on 07/11/2016.

Types of Diseases

Seed Diseases: Loose/Covered smut, Bunt, Seedling blight
Foliar Diseases: Rhyncosporium, Ramularia, Net blotch, Brown rust, Yellow rust, P. Mildew, Septoria
Stem based diseases: Eyespot, Fusarium
Foot/Root diseases: Take-all, Fusarium
Ear diseases: Fusarium, Ergot. Foliar diseases can also affect the ear (Septoria, Yellow/Brown rust, P. Mildew)
Viral Diseases: BYDV

Questions about diseases

What are rusts? (This requires further detail)
What is a haustoria? Function? (Requires further detail)
What is a biotroph? (Requires further detail)
What is an obligate parasite? (Requires further detail)
What is a Heteroecious parasite? (Requires further detail)
What are smuts? (Requires further detail)
What is covered smut? (Requires further detail)
What is loose smut? (Requires further detail)
What is bunt? (Requires further detail)

Cereal Foot and Root Rots

The fungus is commonly introduced into an area by infected plants or on machinery.
Foot and root rot diseases can survive in the soil for several years as spores.
Complete removal is often difficult or impossible.
Fusarium Foot Rot Complex: F.culmorum, F.avenaceum, F.graminearum, F. poae & M.nivale
Take-All Disease: Gaeumannomyces graminis
Sharp Eyespot & True Eyespot: Rhizoctonia cerealis, Peudocercosporella herpotrichoide
Common Root Rot: Bipolaris sorokiniana

Fusarium foot rot complex

There are many Fusarium species that affect cereals.
These fungi form a complex of diseases on seeds, seedlings and adult plants.
Microdochium nivale (formally called Fusarium nivale) is included in this group of fungi.
Consequences: yield loss, loss in grain quality, mycotoxin contamination

Symptoms

Common symptoms are poor plant establishment (thin crop), root rotting, brown foot rot, and leaf blotching.
Glume blotch and ear blights can be caused by these fungi.
Severe foot rot can affect plants under moisture stress, causing premature ripening and whiteheads.

What is a mycotoxin?

Mycotoxins are toxic secondary metabolites produced by certain fungi.
The term "mycotoxin" usually refers to the toxic chemical compounds produced by fungi that colonize crops.
Examples of mycotoxins and crops they are found in are discussed in the table below.

Table 1. Mycotoxins in Grains and Seeds

(Data from the table in the document)

Trichothecene Mycotoxins

Deoxynivalenol (DON) is an example:
Adverse effect on human and animal health and plant health.
Inhibitors of protein synthesis.

What range of mycotoxin-producing Fusarium species do we have in Ireland?

Based on DNA-and GC-MS-detection methods, species like M. nivale, F. avenaceum, F. graminearum, F. culmorum, and F. poae produce mycotoxins and are present in Ireland.

Legislation and Risk of Ear Blight

Legislation limits the level of certain mycotoxins (e.g., DON) in grain.
The presence of Fusarium ear blight might not always indicate a high risk for mycotoxins in cereal crops.

Seedling Blight

Seedling blight is a fungal infection that can cause seed or young seedlings to rot and die.
There may be brown spots on the coleoptile and/or roots.
Fields might exhibit patches that fail to germinate. Seedlings (if they germinate) may not emerge or turn brown, pinched, and die.
Other symptoms include stunted and yellow growth, or reduced root growth with brown spots on the roots and coleoptile.

Other symptoms

Among the fungi present in the soil are Pythium spp., Fusarium spp., Rhizoctonia spp. Most of the infection is soil-borne but can also be seed-borne.
M. nivale is a primary pathogen in the Fusarium group.

Effects of Microdochium nivale

Microdochium nivale is a key part of Fusarium seedling blight in wheat crops.
Its primary source in wheat crops is the seed.
Wet conditions during flowering and grain formation in a season can increase seed-borne infection risk significantly.

Take-All

Take-all is a cereal disease that infects the plant's roots, blocking conductive tissue, causing water intake problems, and resulting in stunting and yellowing
Characteristic "white heads" may appear in healthy crops.
Affected plants easily pull out of the ground because of poor root development.
Above-ground symptoms include stunted growth and white-heads ("bleached" ears) with low grain yield.

Life Cycle

The fungus survives the winter as mycelium on roots, stubble, volunteer cereals, early autumn-sown crops, or some grass weeds.
Primary infection occurs in autumn from inoculums in the soil. Secondary (root-to-root) infection is mostly seen in spring and summer. The disease spreads from infected seedling roots to developing crown roots as the season progresses.

Factors influencing take-all

Weather: Regional differences in take-all are related to weather, soil type, and cropping systems. Crops on light soils are most affected due to easier spread of the fungus.
Management: Well-managed crop rotations normally control take-all in a succeeding cereal. Ploughing buries take-all inoculum, while min-till exposes soil allowing for quicker infection of a succeeding cereal crop, although leaving a more firm seedbed.
Volunteer cereals and grass weeds: Cereal volunteers and grass weeds carry the take-all fungus through break crops increasing the risk.
Varieties: Take-all inoculum decreases quickly after harvest. Risk is decreased in consecutive crops with later-sown crops potentially at higher risk.

Control

Treat seed with seed treatment fungicides to control disease.
Avoid sowing into previous grass-based ground.
Use crop rotations to avoid growing consecutive cereal crops.

Sharp eyespot - Rhizoctonia cerealis

Sharp eyespot of wheat is caused by the soil-borne fungus Rhizoctonia cerealis.
Symptoms in wheat include sharply defined lesions on the leaves and stems, specifically on the lower stems. Typical symptoms of the disease include a dark margin. Often, a dark, diffuse, central 'pupil' is visible.
Rhizoctonia cerealis does not produce spores but instead has mycelium branching at right angles.
Eyespot reduces yield and grain quality by restricting water and nutrient intake. Severe eyespot can cause lodging (stem weakness)

Bipolaris sorokiniana - Common Root Rot

Bipolaris sorokiniana is a saprophyte that can infect barley, spring wheat, rye, and weed and grass species.
Wheat and barley are of most economic importance in the case of this infection.
Common root rot occurs in cereal-growing, warmer areas.
Initial symptoms in seedlings often originate from seed or from soil borne conidia. Dark brown lesions appear on the outer coleoptile tissue and/or on the leaf base. Coalesced lesions may result in long areas of necrotic tissue. Entire seedlings may die but surviving plants will only show stunted growth.
Sporulation of spores is typical in infected regions of leaf blades.

Life Cycle of Bipolaris sorokiniana

The fungus overwinters primarily as mycelium on infected stubble and grass weed volunteers, acting as an inoculum source.
It can also survive as mycelium in soil or crop debris.
The sexual stage (Cochliobolus sativus) is largely insignificant in the disease cycle.
Primary inoculum includes mycelium from infected seed, conidia in the soil, and conidia on the seed surface.
Conidia germinate in the presence of susceptible hosts (like roots or coleoptile), initiating primary infection.
B. sorokiniana infects host tissue directly or through natural openings or wounds.

Control of Root Rot

Historically cultural methods (e.g., crop rotation) have been significant in controlling eyespot.
Now there is increasing importance of cultural control because of increased non-cereal break crops and reduced fungicide use.
Seed treatment is often used in the prevention of root rot.

Summary of Diagnostic Features

(Table from slide 111 that summarizes the main diagnostic features of the stem base pathogens)

Causal Organisms, Symptoms, and Spores

(Table from slide 112 that relates causal organisms, symptoms, and spores for Take-All, Sharp eyespot, and Common root rot.)

References

AHDB publications: https://cereals.ahdb.org.uk/
Diseases of Small Grain Cereal Crops: A Colour Handbook by T.D. Murray, David W. Parry, Nigel D. Cattlin

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on mycotoxins, their effects on animals, and the fungi responsible for contamination. This quiz explores the detection methods, environmental factors influencing growth, and legislative aspects related to mycotoxins. Perfect for students and professionals in agricultural sciences.