Outline
I. Observe your situation
II. Gather data from literature
III. Develop a testable hypothesis
IV. Test your hypothesis
V. Analyze data and determine whether
supports hypothesis or not
Why the scientific method?Useful for solving certain types of problemsMethodological: Françesco Redi and Louis
Pasteur used the scientific method to disprove the widely-held idea of “spontaneous generation” (that life arises from nothing)
Technological: In 1600’s the invention of microscope permitted viewing of germ cells
I. Observation is key
Look at problem- invest in a hand lens for insect and disease problems
Pattern of plant problem on the plantPattern of plant w/problem in the fieldWhat are the possible causes?What can we test for?
Observe the plant closely
Dark brown collar near soil line (crown) of plant
Plant can fall over Photo is of soybean
damping off
Observe the pattern in the field
You notice that low spots in the field have the symptom
Low spots collect water remain damp
II. Check the literatureExtension bulletinsPeer-reviewed articlesTalk to other gardeners or farmers in your
areaAnd to return to an example, Darwin not only
observed and took notes during his voyage, but he also studied breeding and read the works of other naturalists to form his Theory of Evolution.
WSU Extension BulletinDamping off and seed rot of peaSoil-borne fungus complex
Seedlings may be infected and fail to emerge from thesoil. Emerged seedlings are also attacked, causing them towilt and topple over. Water-soaked or brown to blacklesions are often visible on the stem at the soil line. Plantsbecome more resistant to attack as they mature. Damping-off fungi are more of a problem in cold soils with poordrainage, and in conjunction with overwatering.
WSU bulletin:Cultural control of damping off
Do not overwater!Do not plant in soils known to be infested with
damping-off fungi. Mulch to help raise soil temperature. Plant in warm, well-drained soils during warm, dry
weather (when possible). Plant shallowly to encourage quick seedling
emergence and growth.
--WSU publication
III. Formulate a hypothesis
Hypothesis is a statement that has two parts: Need a) testable explanation for the b)
observationNeeds to be able to be tested by an
experimentObservation Yellowing and death at crown
(where stem meets the soil) is due to damping off testable experiment
HypothesisThe observed symptoms (lesions at soil line,
yellowing) are due to damping off caused by a complex of fungi (Pythium sp., Rhizoctonia solani and Fusarium sp.).
What you observe is the effect and the hypothesis is the potential cause
Multiple hypotheses should be proposed wherever possible, e.g. “The observed symptoms are due to Aphanomyces root rot or an insect.”
IV. Test the hypothesis
Isolate the fungi from the diseased tissueReinoculate (apply fungi to) peas under
sterile damp soil conditions Observe symptoms-- are they the same?Re-isolate the same fungus complexThis process ascribing causality of the
pathogen with the symptoms is called “Koch’s postulates”
• Broth experiment to disprove spontaneous generation
– broth in open flash (control treatment)
– broth in closed, sterile flask (experimental treatment)
• Data demonstrated that spoiled broth an microbes were present in open flask only in repeated tests (repetitions)
• Therefore microbes did not arise by spontaneous generation
• Conclusion(s): Organisms do not arise by spontaneous generation in this manner. To quote,
– “Life is a germ, and a germ is Life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.”
--Louis Pasteur
Three essential ingredients of a scientific experiment1) Treatment group
Pea plants are inoculated using agar with fungus complex
2) Control group ONLY difference between the two is only the
ONE variable you wish to test For example if you have the fungi on agar blocks
and you are using the blocks for inoculation then your control is ….
3) RepetitionsWhy are repetitions needed?
Do all plants with symptoms have the pathogen Does the fungus or pathogen complex cause the
disease Environment: Does damping off arise only in damp
spots
How many times do I need to repeat experiment? Depends on variability in system
A further hypothesisYou read in the literature and notice in
previous plantings that a number of varieties of pea (in a variety trial) that smooth-seeded varieties have greater problems with damping off than wrinkled. You set out to test some new smooth and wrinkled pea varieties, as we will.
V. Determine if the results support the hypothesis
Hypotheses can be proven wrong/incorrect, but can never be proven or confirmed with absolute certainty. They are “supported by the experimental results” Impossible to test all given conditions, and
someone in the future may find a condition under which the hypothesis does not hold true
Research is cumulative and progressive. Scientists build on the work of previous researchers, and one important part of any good research is to first do a literature review to find out what previous research has already been done in the field. Science is a process — new things are being discovered and old, long-held theories are modified or replaced with better ones as more data/knowledge is accumulated.
That’s nice but how can I make my results predictive?Another way to say this is “generalizable”This is where the compost tea experiment
last quarter suffered-- not predictive the worm bin compost (valid unto itself) and
other compost were only one example, but this was a preliminary experiment
How to make the predictive case
More tests ie more round vs. wrinkled seeds inoculated and under damp conditions Hypothesis-- Smooth peas on the market have a
greater tolerance to damping off. Has a predictive or generalizable result
ultimately
A theory...“..is a generalization based on many observations
and experiments; a well-tested, verified hypothesis that fits existing data and explains how processes or events are thought to occur.” Predictive May be modified with new information “Theory” in colloquial language means something not
solidified, but it is much more tested than hypotheses!
The role of serendipity or a positive, unexpected result Sometimes serendipity (Serendib = former
name for Ceylon) happens“Chance favors the prepared”Important to be an observer, especially
where your data doesn’t fit your hypothesis!
Scientific method for round vs. wrinkled peas and damping off
I. Observe your situation
II. Gather data from literature
III. Develop a testable hypothesis
IV. Test your hypothesis: treatments, control,
repetitions
V. Analyze data and determine whether
results support hypothesis or not