Part A - General Plant Pathology and Infection Processes

Question 1

You are provided with four samples of the following genera of plant pathogens:
Phytophthora; Alternaria; Rhizopus and Blumeria.
Three of the samples are on culture plates whereas one sample is on a plant.
There are asexual spores present for each. However, all the names have washed off!
Construct a flow diagram, with text, to illustrate how you would distinguish these four different genera.

Answer 1

Blumeria is powdery mildew and is on the plant.
Alternaria is ascomycota and spetate
Phytophthora is oomycota, zoospores easily recognisable under 40x mag
Rhizopus is mucorales.
Shape of sporangia has collumela on mucorales and not in Pytophthora

Question 2

A rust spore lands on a compatible host plant surface.
Describe what happens next until the point where the fungus obtains nutrients from the host.
In your answer include what stimuli activate the growth of the fungus. Note what differences may occur if it is a cereal host or a dicotyledonous host.

Answer 2

Biotrophs obtain nutrients through haustorium.
The rust spore lands on the leaf of the cereal plant.
The spore germinates and produces a germ tube.
The germ tube grows into the plant tissue and forms a haustorium.
The haustorium absorbs nutrients from the plant.

The haustoria of rust fungi that infect dicotyledonous hosts are typically larger than the haustoria of rust fungi that infect cereal hosts. Additionally, the nutrients available in dicotyledonous hosts may differ from the nutrients available in cereal hosts.

Question 3

What physiological process happens that causes chilling damage in plants?

Answer 3

Reduced respiration rate
Decreased photosynthesis
Increased accumulation of reactive oxygen species
Damage to cell membranes
Reduced protein synthesis
Damage to nucleic acids

Question 4

For each of the three plant parts (roots, vascular system, and fruit), describe a different named disease and/or pathogen that affects such tissue. For each of the three pathogens/diseases, briefly describe how the pathogen infects the plants and how the pathogen is dispersed.

Answer 4

Root:
Can be infected by Phytophthora and nematodes
Root rot is a fungal disease that can cause the roots of plants to rot.
Pathogens can infect plants through wounds or natural openings in the roots. They can also be spread through contaminated soil, water, or plant material.

Vascular system:
Fungi are the most common cause of vascular wilts such as Fusarium, Verticulum and Phytophthora.
Caused by pathogens that enter the plant through the roots and then move up the xylem and then block the flow of water and nutrients. Pathogens can be spread by water, air, plant debris & insects.

Fruit:
Mostly caused by fungi including, Botrytis, Colletotrichum, and Penicillium.
Some pathogens, such as fungi, can enter the fruit through wounds. Other pathogens, such as bacteria, can enter the fruit through water splash. Still, other pathogens, such as viruses, can be transmitted by insects or other vectors.
Fruit-infecting pathogen can be dispersed by water, air, fruit debris, insects & humans (carrying infected fruits around).

Question 5

Lack of thriftiness in a crop plant may be due to biotic (pests and pathogens) or abiotic causes. What abiotic factors could contribute to each of the following plant disorders and explain why?
a) Vein clearing of new foliage growth
b) Wilting
c) Necrotic lesions on citrus fruits

Answer 5

a. Nutrient deficiency, oil pH level & water stress
b. Water stress.
c. Water stress, soil salinity & cold stress.