BOT 350: Introductory Plant Pathology
Fall, 2004
Midterm 2
100 points
(40) 1.
NAME ____________________________________
Lab time: 9:00 11:00 (Nate) 11:00 (Ben) 2:00
(circle)
Host resistance
a. Host resistance is often classified into two major types: vertical (specific recognition type) and
horizontal (concert of defenses type). Briefly compare and contrast these two types.
b. Vertical resistance is said to be unstable because it “breaks down” over time. Explain.
c. List two diseases that have been used in lecture as examples when discussing Vertical (specific
recognition type) resistance.
1.
2.
Are the life strategies of the pathogens that cause these diseases best described as ‘obligate parasites’
or facultative saprophytes?
Why is Vertical resistance generally most useful for controlling diseases with the life strategy that was
listed?
d. List three measures or strategies that can be taken to prolong the effectiveness of Vertical resistance.
1.
2.
3.
e. Vertical resistance is based on the gene-for-gene hypothesis. This idea states that the product of a
single gene in the host specifically recognizes the product of a gene in the pathogen.
The following is a table of disease reactions on a set of perennial ryegrass cultivars inoculated with
several isolates of the stripe rust pathogen.
Disease response of pathogen isolate:
Host cultivar/
contains R-gene:
1
2
3
4
5
6
7
8
‘Tuff-turf ‘
‘StayGreen’
‘Taste-Great’
‘Less-Filling’
S
R
R
S
S
R
S
R
S
R
R
S
R
S
S
S
R
S
R
S
S
S
S
S
R
S
R
R
S
R
R
S
R1, ?
R2, ?
R3, ?
R4, ?
1. How many races of the pathogen are there
?
2. Could additional races exist within this collection of pathogen isolates? If yes, what would you
need to do to show this?
3. From the information given in the above table, indicate on the table below the type of reaction (R
or S) these isolates would produce on a host with the genotype shown below.
Disease response of pathogen isolate:
Host cultivar/
contains R-genes:
‘Rust-buster’
R1,? R2,? R3,? R4,?
1
2
3
4
5
6
7
8
(20)
2. Disease development in populations of plants.
a. On the graph provided below, draw a generalized disease progress curve for a polycyclic disease and
label the axes. Label the 3 phases of the curve and state the factor which limits the speed of increase
for each phase.
b. For each of the graphs provided below, draw your generalized polycyclic disease progress curve from
above and also draw a second curve to illustrate the effect of different management strategies.
1. Vertical host resistance
2. Horizontal host resistance
c. Briefly explain the reasoning behind your second curve for each graph.
1.
2.
3.
3. Sanitation
(20)
3. Bacterial plant pathogens
a. Bacterial pathogens do not form specialized survival structures for overwintering. What are three ways
bacteria survive unfavorable conditions?
1.
2.
3.
b. The phase of growth called the ‘epiphyte phase’ is important to many bacterial pathogens.
1. What does meant by the term ‘epiphytic phase’?
2. Why does the requirement for an epiphytic phase make some bacterial pathogen susceptible to
biological control?
3. How is the epiphytic phase involved with the ice nucleation phenomenon exhibited by the bacterial
pathogen, Pseudomonas syringae?
c. To distinguish and identify bacterial pathogens, a series of tests is commonly performed. If the
following tests were conducted, what does the test tell us about each of the listed bacterial pathogens:
Pseudomonas canker
and leaf spot pathogen
Injection of
bacterial
suspension into
tobacco leaf
Growth on
a pectin-based
medium
Examination of
bacterial colonies
under a black light
Ability to grow in
a liquid medium
sealed off from air
by a layer of oil
Soft rot Erwinia pathogen
(20)
4. Rust diseases
Please answer the following questions about stem rust of wheat.
a. Name the pathogen that causes stem rust of wheat (genus and species):
b. In the drawing, label the structure/spore types in the blanks provided.
c. Is it a microcyclic or a macrocyclic rust?
d. Is it autoecious or heteroecious?
e. Is this a ‘monocyclic’ or ‘polycyclic’ disease?
f. What type of parasite is it?
g. What is the overwintering spore?
h. What type of spore initiates infection on barberry?
i. The secondary inoculum consists of what type of spore?
j. When and in what structure does meiosis occur?