Reproductive isolation between lineages and its applied
Sexual Reproduction in the genus Phytophthora.
- Historical importance of Phytophthora.
- Modern removal of geographical barriers to genetic
- Repeated introduction of Phytophthora infestans
to North America and Europe (A1 in 1840’s).
- Worldwide transport of plant and plant products (and
- Importance of mating between previously independent
lineages of Phytophthora.
- More virulent potato pathogens (asexual to sexual
populations of Phytophthora infestans).
- Origin of new pathogens by interspecific hybridization.
- The anatomy of mating in Phytophthora.
- Oogonium, female structure (see right)
Anteridium, male structure (see right)
Figure 1 - Male and Female structures of Phytophthora
- Bisexual fungus-like oomycete
- Mating types A1 and A2
- Life cycle (see figure below).
Figure 2 - Life Cycle of Phytophthora
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Experiment to investigate pre-zygotic isolating mechanisms
- Goal: to investigate pre-zygotic barriers to
reproduction by experimentally crossing isolates of Phytophthora
that differ in their degree of phylogenetic relatedness.
- Relatedness of isolates (below)
D. E. L. and Duncan, J. M. 1997. Mycological-Research 101:667-677
| A2 P. infestans (Mexico [6636 or 510])
| A1 P. infestans (Mexico)
| A1 P. infestans (The Netherlands)
| A1 P. mirabilis (Mexico)
| A1 P. parasitica (North Carolina)
| A1 P. drechsleri (North Carolina)
| A1 P. cinnamomi (North Carolina)
Preparing mating crosses:
- STEP 1: Label bottoms of 7 small petri plates with:
- Two parallel lines that are 1.2 cm apart (see below)
- One line identified as A2-P. infestans.
- The other line identified as A1-“name of other species”.
- The 7th plate get two A2-P. infestans as a
NEXT TIME: We will use microscopes to quantify the
number of oogonia and antheridia produced in the
- STEP 2: Cut out strips of agar containing Phytophthora
- The strips should be about 1.0 x 0.3 cm.
- Cut the strips from the nearer the edge of the plate.
- You’ll need 8 strips of the A2-P. infestan
- 1 strip of each of the A1-isolates.
- STEP 3: Place the strips upside-down on the agar surface
above the lines you drew and labeled.
- STEP 4: Wrap the plates with a strip of Parafilm and
store them at 18°C for 1 week.
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Reproductive Isolation in Phytophthora - Data Collection
- STEP 5: View the crosses
- Invert the petri dishes on the microscope stage
- STEP 6: Quantify mating
- Transect the petri dish between the two samples of
Phytophthora using the 10x objective of your microscope.
- Count all the oogonium/antheridium pairs that enter
the field of view.
- Be sure to discriminate between oogonium/antheridium
pairs and sporangia.
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