Name:
Lab time:
(circle)
9:00
11:00
2:00
Botany 350/550 Midterm I
Oct. 22, 20
(100 points - each page is worth ~25 points – some bonus points on last page)
1. Draw below a POLYCYCLIC disease cycle for EITHER an Oomycete or Ascomycete
pathogen that we observed or discussed in class.
a. Provide the name of disease
(3)
b. Include in your drawing ONE PRIMARY cycle and a SECONDARY REPEATING cycle. (4)
c. Accurately
draw structures appropriate for your chosen pathogen. (4)
d. Include these terms in your diagram: overwintering, infection, symptom expression,
reproduction, dissemination. (4)
e. With brackets ‘{
}’ denoting the beginning and the end, indicate the incubation period,
and the latent period (generation time). Be sure to label your brackets. (4)
f. Describe below a second, alternative PRIMARY CYCLE that might be used by your pathogen
(2)
g. For part ‘a’, what pathogen structure(s) is(are) the primary inoculum?
(2)
h. If the disease cycle in part ‘a’ was monocyclic (and not polycyclic), what part of the disease
cycle would be missing? (2)
2. a. In the box, draw the disease triangle and label each corner (one word is sufficient): (3)
b. Interpret the drawing (what does it mean?): (3)
c. Sometimes, this concept is depicted as a pyramid with the inclusion of a 4th component, time.
Why is time important to the concept of disease? (Hint: think about the definition of disease.)(3)
3 A. Answer questions related to a report of a new disease: First report of Southern blight caused
by Sclerotium rolfsii on Jerusalem cherry (Solanum pseudocapsicum) in Europe. (16pts)
Jerusalem cherry has recently become popular as a potted ornamental plant in Italy. During the
summer of 2009, a sudden wilt of 60-day-old plants was observed in Northern Italy, an area of
intensive floriculture. Initial symptoms included stem necrosis at the soil line and yellow and tan
discoloration of leaves. As stem necrosis progressed, infected plants wilted and died back.
Necrotic stem tissues near the soil line were covered with whitish mycelium that differentiated into
reddish brown, spherical sclerotia. Sclerotium rolfsii was consistently isolated from the surface of
symptomatic stem sections that were first disinfected for 1 min in 1% Clorox and then plated on
potato-dextrose agar (PDA) amended with 100 ppm streptomycin sulfate.
1. What is the primary symptom? (2 pts)
2. What is (are) the secondary symptoms? (2 pts)
3. What is the difference between a primary symptom and a secondary symptom?
e.g. define the terms. (2 pts)
4. What is (are) the signs associated with the disease? (2 pts)
5. What is the difference between a sign and a symptom? (2 pts)
7. What is the name of the disease? (1 pts)
8. What it the apparent cause of this disease? (1 pts)
9. This pathogen is a necrotroph. Define necrotroph. (2 pts)
10. This pathogen is a facultative saprophyte. What is the difference between a facultative
saprophyte and a facultative parasite? (2 pts)
3. a. Match the defense used by plants against pathogens (left hand column) with the correct
descriptor(s) in the right hand column. Maximum number of correct answers per description is 4;
the minimum number is 1 (14 pts).
EXAMPLE
A. Wound papillae
B. Systemic acquired
resistance
C. Cuticle thickness
D. Hypersensitivity
E. Preformed phenolic
inhibitors
F. Phytoalexins
C, E
constitutive
induced
biochemical
structural
local
manifested throughout the plant
type of program cell death
catechol
pathogenesis-related proteins
anti-microbial molecule
callose deposition
salicylic acid
dissolved by fungal enzymes
interferes with penetration peg
frequently triggered by isolate-specific recognition
b. For the induced defenses that you listed in part ‘a’, indicate approximately when they occur on
the timeline of infection (i.e., what is the order in which these event occur and do they occur
before or after the fungus is inside the plant). (4)
Time-line of infection
Pre-fungus penetration
Post-fungus penetration
Host
response:
c. The most common method for entry of plants by fungal pathogens is direct penetration through
the leaf cuticle and cell walls.
a. What four developmental events or steps must occur for the spore to successfully infect an
epidermal cell of a susceptible host? (4)
b. What are two other routes or plant locations which fungal pathogens can take to gain entry
into a plant? (2)
c. What are two types of biochemical compounds used by fungal pathogens use to initiate the
disease process? (2)
4. True/False (24 pts) (Also, if FALSE, then
editing the statement).
a one half point bonus for correctly
a)
The Ascomycetes are also known as the "water molds."
b)
The cuticle is an example of an induced host defense mechanism which functions to
hinder direct penetration by fungal pathogens.
c)
A obligate saprophyte is a pathogen that kills host cells, often in advance of their
colonization, and lives off the breakdown products of dead cells.
d)
A sporangium is an asexual spore bearing structure in the Oomycetes
e)
An apothecium is a small, mushroom-shaped fruiting body in the Ascomycetes in
which conidia are produced.
f)
A haustorium is a structure produced by Oomycete and fungal pathogens that have
a necrothrophic life strategy.
g)
Phytoalexins are chemicals produced by fungi to disrupt physiologic processes in
their host.
h)
Introduction of exotic, non-native pathogens has caused local extinction of plant
hosts.
i)
Plant pathogens can restrict economic trade of plant products.
j)
Oomycetes have septate hyphae.
k)
Tyloses are an example of a constitutive structural defense mechanism utilized by
plants.
l) _______Some Ascomycetes produce chasmothecia (cleistothecia) that serve as
overwintering structures.
m)
Host, environment, and soil type comprise the three corners of the disease triangle.
n)
The hypersensitive response is an example of an induced systemic defense
response.
o)
Disease is a disruption of a physiological process resulting from a momentary
irritation induced by a causal factor or factors
p)
Sexual fungal spores are typically involved in repeating cycles of infection.