Koch's Postulates in Plant Pathology - Step Three

Summary

The video explains step 3 of Koch’s postulates, where a pathogen, isolated in pure culture, is reintroduced to the same plant species to confirm its role in causing disease. The process involves sterilizing tools, making controlled wounds on a healthy apple, and inoculating it with the pathogen. A control wound is also created using sterile agar to differentiate between the effects of the organism and the procedures. The inoculated apple is incubated, and symptom development is observed daily to confirm the pathogen's causal relationship with the disease.

Takeaways

• 😀 Step 3 of Koch's postulates involves re-inoculating the same plant species with the pure culture of the organism to reproduce the disease symptoms.
• 😀 A scalpel, alcohol, matches, an alcohol lamp, paper towels, pure culture, parafilm, a digital camera, and a notebook are needed for the inoculation process.
• 😀 Document the appearance of the pure culture through written description or photographs in the lab notebook.
• 😀 Surface sterilize the apple using alcohol to ensure it is free from contaminants before inoculation.
• 😀 Make small wounds on the apple using a sterilized scalpel to create favorable conditions for infection.
• 😀 One of the wounds should be marked as the control, where clean agar (no pathogen) will be placed to verify the effects of the inoculation.
• 😀 Flame-sterilize the scalpel between each step to avoid cross-contamination during the inoculation process.
• 😀 Place plugs of the pathogen's hyphae into the wounds on the apple to inoculate it with the pathogen.
• 😀 Use parafilm to cover the inoculated wounds to create a sealed, favorable environment for infection.
• 😀 Incubate the inoculated apple and observe it daily for symptom development as part of the experiment.
• 😀 The goal is to determine if the pathogen is responsible for the disease symptoms by observing if the same symptoms appear on the inoculated apple.

Q & A

What is the purpose of re-inoculating the plant in Koch's postulates?

The purpose of re-inoculating the plant is to reproduce the symptoms of the disease on a healthy plant using the organism grown in pure culture. This helps to confirm the organism as the cause of the disease.

What materials are needed for Step 3 of Koch's postulates?

The materials needed include a scalpel, alcohol, matches, an alcohol lamp, an apple of the same variety as the diseased one, paper towels, the pure culture, parafilm, a digital camera, and a notebook for documentation.

Why is it important to document the appearance of the pure culture?

Documenting the appearance of the pure culture helps to track its characteristics and provide a reference for future steps or analysis, ensuring accurate results and reproducibility.

How do you inoculate the apple during this experiment?

Inoculation is done by making small wounds in the apple and placing plugs of the hyphae from the pure culture into those wounds. This creates favorable conditions for infection.

What is the purpose of surface sterilizing the apple and scalpel?

Surface sterilizing the apple and scalpel ensures that no other microorganisms interfere with the experiment, allowing any observed effects to be attributed solely to the organism being tested.

What is the role of the control in this experiment?

The control involves placing clean agar, without any pathogen, into one of the wounds to ensure that any effects observed on the apple are caused by the organism and not by the inoculation procedure itself.

Why is it necessary to flame sterilize the scalpel multiple times?

Flame sterilizing the scalpel between each inoculation helps prevent cross-contamination between samples and ensures that the scalpel remains free from any foreign microorganisms that could interfere with the results.

What is the function of parafilm in this experiment?

Parafilm is used to cover the inoculation sites on the apple to maintain a favorable environment for infection by preventing contamination and moisture loss, which supports the growth of the pathogen.

How long should the apple be incubated after inoculation?

The apple should be incubated for a period that allows symptom development to occur, with daily observations to monitor any changes or disease symptoms.

Why should you use the same variety of apple as the diseased one?

Using the same variety of apple ensures that the plant's response to the pathogen is consistent with the original infection, which is essential for accurate results in Koch’s postulates.