1. Amanda Romag, Dr. Harsh Bias, Dr. Nicole Donofrio, Dr. John Pelesko
An experimental and mathematical study of M. oryzae spore germination and dispersal in the presence of host and non-host volatiles
Kyle Stern
Amanda Romag, Dr. Harsh Bias, Dr. Nicole Donofrio, Dr. John Pelesko

2. Magnaporthe oryzae Fungus is also known as “rice blast” disease
Thought to be a potential bio-terrorism weapon during the mid-twentieth century
Kills enough rice per year to feed over 60 million people worldwide
Also infects barley and wheat crops

3. The destructive process
Spore lands on a leaf via dispersal through the air
Spore sticks to the leaf with sticky substance on surface of its body
Germination begins:
Moisture
Hard surface
Dark
Room temperature

4. The destructive process
Spore begins to pump fluids from its body into the end of the germ tube
Causes a swelling at the end of the germ tube
Appressorium develops
Pressure causes appressorium to swell
Penetration peg infiltrates the plant leaf
Fungus invades the plant
Noticeable brownish-yellow lesions in the plant leaves
Plant dies

5. Normal barley leaf

6. After the infection

7. Volatile Compounds Emitted from a plant in gas form
Farnesyl acetate (C17H28O2 ), a volatile of broad bean, inhibits spread of bean rust fungus
Limonene (C10H16) – volatile of rice
Other volatiles?
Gas chromatography/ mass spectrometry
None found yet
Limonene:

8. The Two Assays Germ tube assay
Do volatile compounds assist in M. oryzae germ tube growth?
Do germ tubes grow in specific directions?
Spore dispersal/sedimentation assay
Are spores actively or passively released from their stalks?
Do volatile compounds assist in M. oryzae spore dispersal?
At what velocity and acceleration are spores released?
Is there a particular force causing the release?

9. The Germ Tube Assay Volatile incorporated into water agar
Spore suspension created using sporulating colony
Spore suspension dropped on empty plate of plain water agar
Strip of volatile in water agar cut out and placed in plate containing spore suspension

10. The Germ Tube Assay
Plate sealed and placed in dark drawer for 24 hours
Viewed at 6.3x magnification under dissecting microscope

11. The Germ Tube Assay

12. The Germ Tube Assay

13. Concentration Gradient
Volatiles must diffuse into the agar where the spores are germinating.
The concentration gradient of a compound in water agar, C(x,t), is found via the following partial differential equation:
Spores
Volatile
Solution:

14. The Dispersal & Sedimentation Assay
Empty Petri dish prepared with two sterile glass slides
V8 agar cut in half through the diameter and placed directly on top of glass slides
Side of V8 agar perpendicular to bottom of dish swabbed with sporulating M. oryzae
Volatile placed in non-control plates

15. The Dispersal & Sedimentation Assay
Plate left unsealed and placed in fungal growth chamber for eight to ten days
Viewed under dissecting microscope
M. oryzae

16. The Dispersal & Sedimentation Assay

17. The Dispersal & Sedimentation Assay

18. Germ Tube Results
Initial results show that germ tube growth direction is random

19. Germ Tube Results Rose Plot
Random
N = 100
M. oryzae
M. oryzae
Farnesyl Acetate
N = 27
Limonene
N = 45

20. Germ Tube Results Rose Plot
N = 1000
N =

21. Dispersal & Sedimentation Results
The Volume of an M. oryzae Spore
- 30 spores measured using ocular micrometer
Mean length: μm
Standard deviation: μm
Mean width: μm
Standard deviation: μm

22. Dispersal & Sedimentation Results
The Volume of an M. oryzae Spore
- Is a spore ellipsoidal or something else?

23. Dispersal & Sedimentation Results
The Volume of an M. oryzae Spore

24. Dispersal & Sedimentation Results
The Volume of an M. oryzae Spore
Let w = h
V = (πlwh)/6 = μm3

25. Dispersal & Sedimentation Results
The Mass of an M. oryzae Spore
m = ρV
Let ρ = 1000 kg/m3, the density of water
m = 1000 * x kg
m = x kg

26. Dispersal & Sedimentation Results The mechanics of spore dispersal
a = radius of the spore,
μ = absolute viscosity of air at room temperature,
K = shape factor of the ellipsoid given by:
Solution:

27. Dispersal & Sedimentation Results The mechanics of spore dispersal
Velocity of a spore in freefall:
Time it takes a free-falling spore to reach the ground: between 70 and 110 seconds.
Terminal vertical velocity:
between 56.96μm/s and 90.86μm/s downward

28. Dispersal & Sedimentation Results Distribution of Dispersing Spores

29. Dispersal & Sedimentation Results Distribution of Dispersing Spores
Control
N = 1340
Mean:
Std. Dev.:
F. Acetate
N = 68
Mean:
Std. Dev.:
Limonene N = 289
Mean:
Std. Dev.:

30. Dispersal & Sedimentation Results Random Walk of a Spore
A spore that does not avoid the block of agar will hit it and either
stick to it
bounce off of it

31. Dispersal & Sedimentation Results Random Walk of a Spore
The distributions are almost identical.
Stick, N=10000
Bounce, N=10000
Frequency
Frequency
Simulated Distance
Simulated Distance

32. Conclusions Spores are actively released.
Some force is pushing them from their stalks.
The presence of limonene is assisting in the dispersal process.
Germ tubes grow in random directions regardless of any volatiles present in the assay.

33. Future Work GC-MS testing on rice, lima bean, and barley plants
Determine the diffusion coefficients of the volatiles
Determine the underlying force causing spores to disperse

34. Future Work
Direct extraction of volatiles

35. The Dispersal & Sedimentation Assay
Optimize spore dispersal assay so that healthy leaves can be placed in the dish with the fungus

36. References
1 Trail, F., Gaffoor, I., Vogel, S “Ejection mechanics and trajectory of the ascospores of Gibberella zeae”. Fungal 42,
2 Clarkson University. “Drag Force and Drag Coefficient”. <
3 Mendgen, K., Wirsel, S., Jux, A., Hoffmann, J., Boland, W “Volatiles modulate the development of plant pathogenic rust fungi”. Planta 224,

37. Acknowledgments Dr. Harsh Bais Dr. Nicole Donofrio Dr. John Pelesko
Thanks:
Howard Hughes Medical Institute
University of Delaware Undergraduate Research Program
University of Delaware Department of Mathematical Sciences
University of Delaware Department of Plant and Soil Sciences
Dr. Harsh Bais
Dr. Nicole Donofrio
Dr. John Pelesko
And…

38. Acknowledgments
My awesome lab partner, Mandy, who had to put up with me.