mmhsharrisspring2019 project 1
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Joined 27 Feb 2019
Project by group mmhsharrisspring2019
Info
| Explore |
Work on this next! What do we know about plants from our experiences outside of school? What have we discovered in class and background research? What questions about plants interest us? |
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| Research Question | We wanted to investigate if Pcc could infest, then infect sweet potatoes, a different host than regular potatoes. We wanted to see if changing the host plant product affects the transfer of bacteria into the host, or if other plant products could become infected by Pcc. |
| Predictions | Sweet potatoes will be susceptible to bacterial soft rot, as caused by Pcc, since they share some characteristics with common potatoes. Also, since Pcc is present in soil, so it is reasonable to believe that sweet potatoes will come into contact with the bacteria and become infested, then... |
| Experimental Design | Materials: - Toothpicks marked at .75” from the bottom - 3 sweet potatoes (roughly 5-8” in length, 2-3” in width) - Paring Knife - 6 Zip-lock quart-sized freezer bags - A sharpie - Paper Towels - Inoculum - Tap Water Procedure: 1. Using the paring knife, cut each potato in half... |
| Conclusion | We conclude that further testing is required to accurately determine if bacterial soft rot, caused by Pcc, can occur in sweet potatoes. We may not have acquired bacterial soft rot in our sweet potatoes because the inoculum we used was collected from Russett potato's soft rot. We know that the... |
| About this Project |
This group showed so much enthusiasm and went beyond their initial investigation to include anything that might be infecting potatoes, including mold. They posted many photographs and spent quality time communicating with their mentor. Though the results of the actual experiment were not... |
Updates
As this research project is now in the final stages of wrapping-up, we wish to thank everyone who participated in this inquiry; the students, mentors, teachers and others behind the scenes. We appreciate all of your efforts and contributions to this online learning community.
Scientific exploration is a process of discovery that can be fun! There are many unanswered questions about plants just waiting for new scientists to consider, investigate, and share.
After the end of the session, we will be updating the platform and archiving groups and projects, after which time new updates/posts will not be able to be added to projects or groups. Please come back and visit the PlantingScience Project Gallery anytime to view this project in the future. You can search the Gallery by keyword, team name, topic, or school name.
Good bye for now.
Warm regards,
The PlantingScience team
It’s great to see that teams from your school are wrapping up and posting conclusions. Enjoy the final stages of your project, and feel free to post any final comments or questions you have for your mentors.
I sent on your info and photos to Lina Quesada, a professor at North Carolina State University who studies sweet potato diseases. She said that the rot and white mold you saw on the sweet potatoes was likely Geotrichum sour rot of sweetpotato (https://content.ces.ncsu.edu/geotrichum-sour-rot-of-sweetpotato). This fungus is normally seen in anoxic (no oxygen) environments. Since your sweet potatoes were kept in plastic bags, it could have helped it grow. She said that they are seeing a lot of this disease on sweet potatoes this year because of the hurricane that they had in North Carolina (probably where your sweet potatoes came from) since many farmers fields were underwater (no oxygen) for a long time this summer. It's cool to see how real world events affect the food that you buy in the grocery store.
By the way, our moldy sweet potatoes smelled like yeast, and very sweet and ripe bananas. Does this mean something? We are super curious.
As I mentioned in my other comment, I did some searching and found that sweet potatoes infected with the fungus Rhizopus stolonifer give off a pleasant smell that attracts fruit flies. Since fruit flies also like ripe bananas, I wonder if what you are smelling is due to a Rhizopus infection? I will ask my friend who is an expert on sweet potato diseases and see whether this might be the case. Cool!
Here’s our final update on our sweet potato experiment. We found some mold on each of the remaining experimental sweet potatoes, #2 and #3. Mainly on the ends of the potatoes were where the mold clusters were found. We cut open the potatoes longways and sliced into transverse sections, but no mold correlation was found where we had poked the potatoes with the inoculum two weeks before. There were no signs of soft rot, even though there were lots of brown spots in the tissue that were soft and squishy, but we attributed that to the mold growth! Besides being very white from dehydration, there wasn’t much to observe. We concluded that further testing would be required for accurate results to be attained about our hypothesis.
Thanks for the update, team! So, it sounds to me like there wasn't much reaction in the spots where you inoculated with the bacteria. What does that tell you about the interaction between sweet potato and the soft rot bacteria? We know that the bacteria can infect potatoes (that's where you got the inoculum from). But since sweet potatoes are not potatoes (despite the similar name), we weren't sure what would happen.
The mold could be Fusarium, another plant pathogen that is common on sweet potatoes. Since you kept them in a moist environment, you gave the fungus a chance to infect the sweet potato. Check out this website for common sweet potato diseases: https://ncsweetpotatoes.com/sweet-potato-industry/growing-sweet-potatoes-in-north-carolina/diseases-disorders/
In particular, check out the description of Rhizopus soft rot (different from potato soft rot): "Infected tissue rapidly becomes soft, stringy, and watery with a pleasant fermentation odor. In a few days, “whiskers” consisting of fungal strands and spores appear. Fruit flies are attracted to the rotting roots." You know what else fruit flies are attracted to? Bananas. I wonder if what you are smelling is due to this fungal infection?
Great observations!
Hi Dennis!
The potato would probably lose some mass if it got infected with bacterial soft rot, would it not? Just since the bacteria would eat away at the tissues of the potato, so it would lose mass! Please correct me if I’m wrong! And we only inoculated sweet potatoes this time around, no potatoes or other vegetables. Do you think that anything will happen to the remaining sweet potatoes? I know that you mentioned since sweet potatoes aren’t related to Russett potatoes, that they might not become infected! Thanks for your help!
I don't think there's a right or wrong answer. I'm not really sure what would happen to the mass. If it's all contained, I don't think it would change much. There might be less potato, but more bacteria, so it would all even out. But if you could remove the bacteria or the infected parts, certainly there would be less potato left.
I don't think I've tried using sweet potatoes before, so I'm not sure what will happen if you keep them longer. It's possible that it just takes longer to get infection, or they might be completely resistant. That's why I said it might be a good idea to use something that you know will get infected as a control for the experiment, like a normal potato.
Today we examined the sweet potatoes after they were incubated for a week. There were no major defects that could be seen on experimental potato #1 when we cut it. We decided that it would be best to wet the paper towels again and wrap them around experimental potatoes #2 and #3 and incubate them for another week. There was one potato that already had some noticeable brown spots and looked very dehydrated, so we decided to turn it into the "fun" potato. The potato was inoculated with tap water on both sides then it was wrapped up in a wet paper towel and inoculated for a week in order to see of there would be changes on the moldy side and on the non-moldy side. We do not have any pictures of the sweet potato before the inoculation because we were not expecting any changes to happen. When we cut the "fun" potato after inoculation, it had a lot of squishy spots and moldy spots, but it did not have an odor. Do you have any idea what happened to the "fun" potato?
So, based on the photos, I don't see much soft rot symptoms. And based on your observations, I would say that your sweet potatoes are pretty resistant to the bacterial infections. Did you inoculate any other vegetables or potatoes as controls? Since sweet potato and potato are NOT very closely related to one another, I would not expect the results to be similar. Did you inoculate any potatoes (not sweet potatoes)?
I like your idea of turning the 'fun' potato into a separate experiment. The squishy spots suggest that there is some rotting going on. It is common that other microbes will take advantage of this and 'feed' off of the rotting parts. This is called 'secondary infection' and is likely why you see some mold at these spots - the bacteria is doing the work of breaking down the plant material and then the mold is just feeding off of this material. The mold itself is likely not a pathogen of sweet potatoes.
One way to test if you have soft rot in your 'fun' sweet potato is to take some of the mushy spots and make more inoculum. Basically you could just scrape some off with a toothpick and poke it into a new sample. It would be best to test this on something that you know will get infected - like a potato (not another sweet potato). This is one of the foundational principles of pathology - being able to take a sample from an infected sample and using that to try to infect another sample. This tells us that it is actually a pathogen (google "Koch's postulate").
Hey Dennis!
Before we looked at our sweet potatoes today, we, as a class, brainstormed some more ideas we could have utilized in our initial project. These might be helpful if other classes are planning on trying this experiment as well!
- Temperature of the control water and Inoculum
- Mass of sweet potatoes
- Distance between each hole
- Exact dimensions of sweet potatoes
- Relative humidity
- Control size of paper towel and how much water qualifies it as “damp”
- Standardize any of these parameters?
That's a great idea.
Temperature is definitely important for disease formation - not only the temperature of the initial inoculum, but also the temperature that the samples are kept at during the experiment. The mass is also a great measurement to take (and pretty easy to do). Do you think the mass of the tuber would increase/decrease/stay the same after being infected with soft rot?
What we do to measure soft rot in potatoes is to cut the tuber at the site of infection to see how large the lesions are. If the distance between the holes is too small, the infected areas could run into one another, which makes it difficult to take accurate readings.
The others that you have on the list are also great. If you can quantitate (what I think you mean by 'standardize') your measurements in any way, it would help in analyzing your results. Quantitative measurements are ones that result in numbers (mass, length, width, etc.). Qualitiative measurements don't really use numbers and instead use descriptions (susceptible, resistant, large diseased areas vs. small diseased areas, colors, etc). Qualitative measurements are difficult to analyze later because it more difficult to compare them between experiments.
These are the pictures from yesterday. We first marked our toothpicks a quarter inch from the bottom so we knew exactly how far to poke them in. Next, we cut the sweet potatoes in half and separated them so one half would be inoculated with water and the other half with the inoculum. We then preoceeded to inoculate the halves the same way we did with the russet potatoes and we will check back up on them in a week. Currently, we are working on the actual writing of the experiment.
Looks good! Did you have to hold your nose the whole time? :)
I don't think I've tried sweet potatoes in this experiment before. I will be interested to see what happens. Sweet potatoes have a lot more sugar in them than regular potatoes, so the bacteria might really like them. But they have less water and more fiber, so I'm not sure. We'll have to wait and see.
Great observations! So, it's been a week and you should start to see some infection, but it depends on the conditions. It sounds like maybe you are starting to see some responses. Pectobacterium does have flagella and they will swim around. So it's likely that you're seeing soft rot bacteria under the microscope (it's a little hard to tell from the photo, so I'm relying on your observations). The corky areas are probably just the potato drying out a bit in the inoculated area, and doesn't necessarily mean you have soft rot there. Soft rot gets its name because the areas get really soft and mushy.
I would say to try a lot of different stuff and see what happens - that's what experimenting is all about. You probably have a lot of inoculum, and it's not difficult to poke a bunch of vegetables or fruit with toothpicks. Sweet potato is a great idea (but you should look up to see whether they are related to regular potatoes - you might be surprised). There are lots of vegetables that are susceptible to soft rot (my cucumbers at home get it all the time), so do a quick shopping trip and pick up a few different things in the produce aisle (or raid your refrigerators at home).
You recall the "disease triangle" I mentioned earlier? In a proper experiment, you should only change one thing at a time. All of your experiments will use the same pathogen (your inoculum), so it cannot change - although you should include a control where you inoculate with no pathogen (just water). So, in your experiments, you can change the host (vegetable), but not the environment or pathogen. Or you can change the environment (temp, light, etc), but not the host or pathogen. It might be a great idea to make an outline of what you want to try so that you can keep track of everything.
Keep in mind that whatever you try, you're going to learn something. So just have fun and do some science! :)
When we examined our potatoes today, we did observe some nuances from the healthy potatoes. They were hard, hollow, and brown, in the shape of the toothpicks that were previously inserted. This appears to be cork formation. There wasn’t an observed smell, either. Just the earthy smell of potatoes was observed. Macroscopically, one spot did actually look like a potato soft rot lesion, and it was a brownish around the edge with grayish white matter growing on the inside. The tissue did look infected! We also looked at it under the microscope at 1000x using oil immersion microscopy. We saw some organisms? or maybe not! We aren’t quite sure what we’re looking at. The pictures of it will be below! Are we seeing bacteria, or something else? And we were thinking about switching the regular potato to a sweet potato, and we theorize that the bacterial soft rot will also occur in sweet potatoes. Do you think we should try this, or a whole other vegetable entirely? Also, instead of that, we were still thinking about the temperature or humidity, too, as factors to change. Do you think these variables would make anything different? Let us know!