| Explore | Soft rot is the most common and contagious form of rot in potatoes, causing an estimated loss of $276 million per year in profits for farmers and companies around the world. The bacteria responsible for soft rot--Erwinia carotovora--is most active in potatoes when in an environment above 50-degrees-Fahrenheit or surrounded by wet or decaying tissue. When placed in an environment that features those bacterial factors, soft rot causes potatoes to brown and blacken and turn from hard to soft and mushy. The Erwinia carotovora bacteria spreads through potatoes' tubers ('stems') and lenticels ('pours'). |
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| Research Question | Is there a significant change in the amount of soft rot present in a potato affected when the potatoes are placed in a hot, cold, and room-temperature environment? Is there a direct relationship between soft rot growth and temperature? |
| Predictions | When potatoes infected with the Erwinia carotovora bacteria are placed in a cold, hot, and room temperature environment, the potatoes in the hot and room temperature environment will show the quickest rate of infection because the bacteria is considered to be more active in warmer environments. |
| Experimental Design | Procedure: We took three large Ziploc plastic bags and labeled each as "Hot", "Room Temp.", and "Cold". Within each large bag, we placed two smaller bags labeled "Yes" for the potatoes that were infected with the bacteria and "No" for our control group in each environment. We then took three potatoes and--without skinning them--cut them into fourths that each weighed 20-21g. The twelve pieces we had were wrapped in wet paper towel and evenly divided among the conditions (4 potatoes per condition, two of which were infected and the other two were the control). The "Hot" potatoes were placed in an environmental chamber that was maintained at 116.8 degrees Fahrenheit. The "Cold" potatoes were placed in a Styrofoam container with ice that was switched out for new ice daily. The ice container was maintained at a temperature of 48.5 degrees Fahrenheit (not including transportation between house and school). The "Room Temp." potatoes were left in the classroom. Since the environmental chamber and classroom would be exposed to different amounts of light (sunlight and artificial light) and the iced potatoes would be in complete darkness (outside of when we changed the ice), we decided the only way to remove light as a potential confounding factor was to place the potatoes in as much complete darkness as possible. The environmental chamber glass panel was lined with black construction paper, the "Room Temp." potatoes were placed in a lab station drawer, and the "Cold" potatoes were left in the styrofoam ice box. After nine days, we took the potatoes out of their respected environments and analyzed any changes we noticed. First, we collected all the qualitative data we could. The "Hot" potatoes had been turned into complete mush (imagine an extremely over-baked potato), the "Cold" potatoes looked and felt surprisingly unchanged except for some obvious and subtle black-discoloration, and the "Room Temp." potatoes had completely browned around their entire exteriors. All three groups smelled like, well, rotten potatoes. The "Hot" potatoes were noticeably the foulest smelling of the three; perhaps, this was because the rot had grown and spread more in the "Hot" potatoes than under the other environments. We then re-massed the potatoes in order to compare them to their initial masses. Unfortunately, the "Hot" potatoes were in such a hot environment for such a longer period of time, that the wet towel we wrapped the potatoes in was actually more-or-less fused with the potatoes to such a degree that it was impossible to remove the paper towel without removing significant chunks of each potato. As a result, we could not accurately re-mass the "Hot" potatoes. However, we were still able to re-mass the "Cold" and "Room Temp." potatoes, observing a major increase in the mass of both set of potatoes. In fact, the "Cold" potatoes had seen an average increase in mass of +4.2g, and the "Room Temp." potatoes had an average increase in mass of +2.47g. When it came to weight, another interesting observation was that the infected "Cold" potatoes gained less mass than the "Cold" control group whereas the infected "Room Temp." potatoes gained more than the "Room Temp." control group. Finally, we took made slides for each conditions infected and control potatoes. Here is a link to a presentation that includes the pictures: https://docs.google.com/presentation/d/1icJtGr8AfEAbMN-glxNwOIyDhnW9mkJiDCwOheXKs0A/edit?usp=sharing We could tell that the "Hot" potato cells had clearly lost or had severely damaged cell walls and lacked any movement under the microscope. The "Cold" potatoes featured very little viral movement under the microscope but maintained its cell walls. The "Room Temp." slides easily showed the most viral movement and had more faded cell walls than the "Cold" potatoes. |
| Conclusion | Taking the data at face value, we can conclude that temperature increases the rate at which soft rot spreads in potatoes because higher temperature environments lead to greater cell well damage, making it easier for the bacteria to spread from cell to cell in the potatoes. This conclusion would also explain why the "Hot" and "Room Temp." potatoes saw the greatest physical change (i.e. due to increased rot growth and expansion). Our conclusion is also supported by the biological understanding that heat increases the rate of cellular respiration due to an increase in kinetic energy. In other words, because the potatoes were placed in a heated environment and because the soft rot bacteria spreads through the tubers of the potato--the potato limb responsible for respiration--the increased cellular respiration would have led to an increase in heat and water in-take--two factors linked to the further spread of soft rot and bacteria in-general. However, this isn't to say our conclusion is perfect, nor is it to say that our experiment is over. Due to the damage done to the "Hot" potatoes and the question of the effects of cellular respiration on the spread of soft rot, further research into both of those factors is required. |