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Importance of Survival Skills

Plants Get Sick

Plants Get Sick


Plants are the backbone of all life on Earth. Take a moment to admire Earth’s scenic beauty and you’ll see that plants make up a very large part of that picture. Millions of organisms, including people, depend on healthy plants for food, clean air, clean water and habitat. Let’s take a closer look at some individual plants. Have you ever sat under a tree and noticed some of the leaves have strange spots on them? Have you ever seen brown patches in your lawn, even after we’ve had a lot of rain? These plants don’t look healthy. And they don’t appear to be damaged by bad weather or hungry animals. What could be happening here? Well it turns out plants get sick just like people get sick. Dr. Laura Jesse is here to show us how to investigate what might be going wrong. For a plant diagnostician the fun really begins when plants start to get sick. At that point it’s really a crime scene. We start to gather background information, look at all the clues, take pictures, gather up all the information we can and start to try to figure out what is going wrong with this plant. Knowing what the plant species is, is one of the most important steps. That’s really easy in a garden like this where all of the plants are labeled, but can be much more difficult out in your back yard. Knowing what the plant species is really helps us narrow down our potential culprits because most plant diseases are host-specific, meaning that they’ll just make a few different species of plants sick. The next step is to actually look at the plant itself and see what clues we can get. Plant diseases affect plants in different ways. We can get spots, we can get wilting, we can get stenting, all sorts of different things. And looking at how that plant has responded to that plant disease really can help us figure out what’s going wrong. So, before we leave the crime scene we definitely want to get as much background information as we can about where the plant is growing because conditions like too much water, too little water, being planted too deeply, all these things can stress the plant and make it more prone to getting sick. And then the next step is we take some of the plant material, we take it into a lab where we have tools like microscopes, reference books and other experts who can help us narrow down exactly what’s going wrong. Dr. Erika Saalau Rojas studies plant diseases in the plant and insect diagnostic clinic at Iowa State University. So, a pathogen we describe as any organism that can cause disease on a plant, very similar to what we call pathogens on humans and animals. There are four main types of pathogens when we talk about plant pathology. The biggest group of plant pathogens is composed by fungi and fungus-like organisms. We also have bacteria, viruses and nematodes. And what we brought here back to the lab to take a look right now is the iris that we saw earlier in the garden. The iris, when you looked at it out in the field, had quite a bit of yellowing, a lot of leaf spots, but when you bring it back into the lab and you get a closer look you can see that the leaf spots are very circular, they’re surrounded by yellowing and they have some brown or tan color in the center. And at this point I’m not sure exactly what could be causing the leaf spots. But if you look closely you can also see that there are some darker spots in some of the bigger lesions. This looks to me like a fruiting body or possibly spores which is pretty characteristic of fungi. So, another main type of pathogen that we also study are bacteria. Back in the garden there was another plant, an oak leaf hydrangea that was also showing some leaf spots. So, we can bring it back to the lab to take a closer look. In this case we did not find any signs that it could be fungal. However, under a more powerful microscope, we can take a closer look and notice some of the signs that are typical of bacterial leaf spots. Here what I have up on the screen is a close-up of the plant and here this part is the leaf tissue and this cloudy looking substance that is over on this side are the bacteria gushing out of the leaf itself. This is a pretty good indication that it is a leaf spot caused by bacteria, most likely not fungi or any other plant pathogen. So, the third group of pathogens that we talk about or study in plant pathology are viruses and this is what we think is going on with this hasta here. And viruses are very unique. You can’t really see them under a microscope. But they do cause some really funny looking symptoms. For example, what is not normal for this plant right here is the wrinkling of the leaves and maybe some of the darker areas and the color patterns. So, one way that we can confirm that it is a viral pathogen without having to use a microscope is using some of these quick, commercial strip tests in which, what we do is cut a portion of the leaf out, put it in a solution and put a test that is already specific to some of the viruses that are common in hasta and see if it gives us a positive or a negative. The final group of pathogens that we study in this lab are plant parasitic nematodes. And unlike the other pathogens that we have reviewed today, nematodes are very small, wormlike pathogens usually associated with the root system of plants. It can be difficult to diagnose nematode problems because they are, for the most part, in the root system, they’re very difficult to see and they can be easily confused with other issues that plants may have like nutrient deficiencies or water problems or all sorts of non-pathogen problems. Knowledge is power when it comes to diagnosing plant diseases. If we can be accurate about what the problem is, we can be much more responsible when we treat it.

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