Part D - Dikarya Flashcards
The diagram below represents the life cycle of a pathogen that caused an epidemic on elm trees in North America and Europe in the mid-20th Century.
a. Which letter represents where karyogamy would occur? (1 mark)
b. What would be the ploidy of the fungus at location “B”? (1 mark)
c. What type of spores are found at “A”? (1 mark)
d. How would you attempt to control this disease? (2 marks)
e. Can you name this pathogen or the disease it causes? (2 marks)
f. Name the type of fruiting body structure at “D” (1 mark)
g. Why did the epidemic occur? (2 marks)
Ascomycota as we can see ascus inside perithecium.
a. C
b. Diploid
c. Ascospores
d. Try and control the beetles to minimise spread.
e. Dutch elm disease
f. Synnema
g. Pathogen introduced from south-east asia
The plant pathogens listed in the first line of the table below are members of the Dikarya. However, they have differences in their life cycles and how they interact with their host. Complete the empty sections labelled A to J
A. Dikarya
B. Haploid
C. Biotroph
D. No, it is local
E. Dormant form
F. In vectors/aphids
G. Uredospores
H. Conidi
I. Acts as re-hydration and germination initiation. Also helps spreading disease
J. Inhibits spread as ascomycetes store their own water supply and rain would wash them off plants.
An apothecium and an acervulus are both open saucer-shaped structures produced by fungi within the Ascomycota. What is the main difference betweenthese structures?
Aecervulus is not as well developed as an apothecium.
Apothecium is better at dispersing spores.
What is a hilar droplet?
A structure that is found on the surface of basidiospores.
Hilar droplets are thought to be involved in the discharge of basidiospores by providing a source of energy and by acting as a lubricant.
Covered smuts caused by Telletia species initially infect which part of a host plant?
A. Leafe
B. Seedling
C. Seed
D. Flower
Flower.
The fungus produces spores that are released into the air and can be carried by wind to other plants. When the spores land on a flower, they germinate and infect the plant. The fungus then grows inside the flower and produces a black, powdery mass of spores. This mass of spores can eventually kill the flower and prevent it from producing seeds.
Describe the main types of both asexual and sexual fruiting bodies that are found in the Ascomycota. Use drawings to illustrate your answer.
Sexual spores in ascus or asci (plural)
Cleistothecium
Perithecium
Apothecium
Asexual spores
Conidium/conidia
Briefly discuss all of the following terms listed below.
In your answer, consider the implications these contrasting definitions may have on disease control.
a) Monoecious versus heteroecious rusts
b) Homothallic versus heterothallic plant pathogenic fungi
Monoecious rusts are fungi that can produce both male and female reproductive structures on the same plant while heteroecious rusts need two different plants to complete their cycle.
Monoecious rusts are harder to control than heteroecious rusts.
Homothallic plant pathogenic fungi are fungi that can produce gametes (sex cells) without the need for a partner while heterothallic fungi need two different individuals to produce gametes. Homothallic pathogens are harder to control than heterothallic as they can reproduce virtually indefinitely.
The powdery mildew fungi are members of the Ascomycota; they are also biotrophic plant pathogens. With regards to powdery mildew fungi explain:
i) how they are able to infect their host and obtain nutrients;
ii) what impact do they have on the host plant and;
iii) how have host plants evolved to defend themselves against powdery mildew fungi?
Powdery mildew fungi are able to infect their host by producing spores that are carried by the wind or by splashing water. Once the spores land on a susceptible plant, they must rehydrate and then germinate to form mycelium. The hyphae penetrate the plant’s cuticle and begin to absorb nutrients from the plant’s cells.
Yellowing of leaves to a curl and eventual fall off. Stunt growth and reduce yield. If infection is severe plant may die.
Plants have evolved to defend themselves in the following way:
I. Production of resistant varieties, naturally-occurring resistance to powdery mildew fungi (selection)
ii. Production of antifungal compounds. These compounds can be produced in the leaves, stems, or roots of the plant.
iii. Constitutive physical barriers such as thick cuticles, waxy coatings, or hairs on the leaves.
Describe how fungi that cause powdery mildew infect a host plant and ultimately how these fungi reproduce through both asexual and sexual spores.
Powdery mildew fungi infect host plants by releasing spores that land on the plant surface. If the conditions are right, the spores germinate and produce mycellium that grows over the surface of the plant. The hyphae will then move along leaf surface and penetrate once it has found a stoma.
Powdery mildew fungi can reproduce both sexually and asexually. Asexual reproduction is more common and involves the production of spores called conidia. Sexual reproduction is less common and involves the production of spores called ascospores.
Rust pathogens can produce multiple different spore types with differing ploidy levels. Describe a rust fungus that produces these different types of spores, name the spore types and indicate their ploidy level.
Puccinia graminis:
Pycniospores: These are haploid spores that are produced in pycnia, which are flask-shaped structures. Pycniospores are used for sexual reproduction.
Aeciospores: These are diploid spores that are produced in aecia, which are cup-shaped structures. Aeciospores are used to infect a new host plant.
Urediniospores: These are also diploid spores that are produced in uredinia, which are raised, rust-colored spots on the leaves of the host plant. Urediniospores are used to spread the rust fungus to other parts of the same host plant.
Teliospores: These are diploid spores that are produced in telia, which are black, powdery spots on the leaves of the host plant. Teliospores can survive harsh conditions, such as winter, and can germinate the following spring to produce pycniospores and start the life cycle over again.
