On May 13th we made our second visit to the UAB Community Garden. We were grateful to have a mild breeze and plenty of water this time around. Our goal was to scout for plants that appeared to be sick and test them for various diseases. Some typical signs of disease in plants include blemishes, rotting, wilting, color change, and withering on the plant surface. Before getting started, Dr. Mukhtar showed us pictures of infected plants in a plant biology textbook to give us an idea of what we were looking for.
We worked in groups of three to scan each plot in the garden for these telltale signs of disease. It did not take long to find plants with symptoms of disease. My group and I first came across a sick pepper plant, basil plant, and bean plant. We snapped off leaves from the plants.
After gathering our samples, we headed over to the testing station where teaching assistant Marie demonstrated how to conduct tests on plants in the field. We used plant pathology test kits by Adgia that included a pouch with two mesh squares inside it and ImmunoStrips®. The pouch contained a buffer solution. The test kits are able to test a sample to see if it is infected with a specific type of disease or condition. To test our samples, we first had to disinfect a pair of scissors using an alcohol prep pad. Next, we cut off a square inch of the infected plant tissue (leaves, in our case) and placed it in between the mesh squares of a pouch specific to the plant (i.e. pepper plant).
With the plant tissue in between the mesh, we rapidly scratched the leaf using a Sharpie marker and a hard surface in order to break down the contents of the leaf and expose them to the buffer.
Finally, we inserted an ImmunoStrip® into the liquid of the pouch and waited until a result appeared.
Marie helps Andrew prepare to use an ImmunoStrip®
The ImmunoStrips® test for specific diseases and work very much like a pregnancy test. A few minutes after sitting in the sample solution, the strips produce one of three test results. One line in the middle of the strip indicates that the test is negative, and the plant is therefore not infected with the disease. Two lines means that the test is positive, and the plant indeed has the disease. No change in the test strip means the test is invalid and did not work. The types of diseases we tested for include cucumber green mottle mosaic virus, pepper mild mottle virus, cucumber mosaic virus, impatiens necrotic spot virus, tobacco mosaic virus, and many more.
The results of two tests conducted on the pepper plant. The plant was tested for tobacco mosaic virus as well as pepper mild mottle virus. As indicated by the single red bands on both test strips, the plant tested negative for both viruses.
It is important to note that we tested only for viral diseases during this garden trip, not for bacterial or fungal plant diseases. Also, since we did not have test strips for each type of sick plant that we encountered, we tested many of our samples for the tobacco mosaic virus, which is a disease that affects plants worldwide. It results in stunted growth for the infected plant and damaged fruit leaves, and flowers. This virus is devastating to crops and, as I have learned, affects several herbaceous plants besides tobacco.
After the first round of testing, my group and I went out to find more sick plants. I found an okra plant that look troubled, and one of my group members found an eggplant.
Although there was a decent number of plants in the garden that presented signs of sickness, all tests performed by the group were negative. This is not to say, however, that the plants tested are not sick. We were limited in the type of plants we tested and the specific diseases that we tested plants for. For example, many basil plants in the garden were discolored and had spotting, but we were unable to test basil plants. Also, interestingly enough, several plants in the garden have been attacked by insects. Many leaves had been chewed on, and lab assistant Maggie found a plant leaf that had been invaded by an insect. The insect dug a visible trail inside the leaf. Dr. Mukhtar determined that the insect was no longer living inside the leaf when Maggie found it. I was unable to get a picture of the leaf, but an example of this condition can be found below.
One important thing that I learned during this trip is the double effect of moisture. Plants, of course, require moisture in order to survive. The interesting thing is that pathogens also require moisture in order to spread. Since many pathogens such as fungi and bacteria are either immotile or only able to move by “swimming,” they must reside in a moist environment if they hope to spread to other plants. So on one hand, water is good for plants since it promotes their survival while on the other hand water can be the means by which disease spreads in a garden.
All in all, I thoroughly enjoyed this trip to the garden. I felt like a detective searching for clues when we scanned the plants for disease symptoms, and I enjoyed working with my fellow OUTPACErs to determine which plants to test. I became familiar with plant pathology kits and can now say that I know how to use one. I am excited to see what I learn next!
Amir and Ciara collaborate to determine if a plant appears sick
A collection of the pathology tests the group conducted in the garden