Throughout the protocol, utilize only conventionally grown ( nonorganic) potatoes. Conventional potatoes are treated with a germination inhibitor, which will prevent potatoes from sprouting when incubated.
(1) A week prior to the experiments, initiate the cultures to acquire inoculum. Cut a potato in half and incubate the halves in an airtight plastic bag with 50 mL of tap water for five days at room temperature. If infected, the potato will be soft to the touch and the liquid will be cloudy with bacteria. Most potatoes will become infected with this approach, so consider incubating between three and five potatoes to collect sufficient inocula for the class.
(2) The day before the lab begins, disinfest the remaining potatoes by soaking in the 10% bleach solution for at least 30 minutes. Ensure that each potato is completely submerged in the bleach solution, and agitate the potatoes occasionally as they soak to remove any bubbles. After incubation, remove the potatoes from the bleach solution, rinse with fresh water, dry with paper towels, and set aside to air dry overnight.
incubate in the same manner as the students’ samples.
(b) Collect the bacterial inoculum by cutting a corner of the culture bag and collecting the liquid in several containers for the students. The bacteria can be stored in a refrigerator and used for at least six weeks.
(1) Discuss and outline the experiment (Table 3).
(2) For each lab group of two to four students, collect at least three disinfested potatoes and ensure that they are free of obvious disease symptoms incurred during shipment and storage.
(3) Dip a clean toothpick into a container of bacterial solution and inoculate the bacteria into the potato by poking the toothpick through the skin. Repeat the inoculation approach to ensure that each potato is similarly inoculated ( i.e., a similar number of toothpick wounds). The same toothpick may be used for all the inoculations, but students must re-dip the toothpick in the bacteria solution prior to each inoculation for consistency.
(4) After inoculating, wrap each potato in damp paper towels and enclose in a sealable plastic bag.
(5) Incubate all potatoes on the benchtop for seven days. If infected, the potatoes will become soft to the touch and produce a pungent odor.
ples should exhibit similar symptoms.
(b) Slice the potatoes through lesions and observe symptoms within the potato (Figure 2B–D).
representative discussion points for students).
If we inoculate a potato with soft-rot-causing bacteria, then __% of the potatoes will be infected with bacteria because _____.