Exploring the Topic of Nematodes with Cynthia Gleason and Rachel Bomberger

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Show Notes & Resources Mentioned:

Contact Information:

Contact Cynthia Gleason via email at cynthia.gleason@wsu.edu. Contact Rachel Bomberger via email at rachel.bomberger@wsu.edu.

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Episode Transcription:

[ Music ]

Drew Lyon: Hello. Welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production. If you enjoy the WSU Wheat Beat podcast do us a favor and subscribe on iTunes or your favorite podcasting app and leave us a review while you’re there so others can find the show too.

[ Music ]

Drew Lyon: My guests today are Cynthia Gleason and Rachel Bomberger. Dr. Gleason is a molecular nematologist who joined WSU Plant Pathology faculty in 2016. She was previously a junior professor in Germany working on nematode secretions and plant immune responses in the model mustard plant called Arabidopsis. Her research at WSU focuses mainly on root knot nematodes, but she has a general interest in all things nematodes. Hello Cynthia.

Cynthia Gleason: Hello Drew.

Drew Lyon: Rachel is the plant diagnostician for the WSU Department of Plant Pathology’s Plant Pest Diagnostic Clinic. The clinic is a year-round resource available to growers, industry, and the general public to help them identify and manage their plant health problems. The clinic works on all but one plant to test for fungi, bacteria, viruses, and nematodes. The clinic can also test soil for select pathogens and perform tests for special issues impacting Washington and the P&W. Hello Rachel.

Rachel Bomberger: Hey Drew.

Drew Lyon: So I have the two of you today because you, Rachel, have been receiving some samples and have found some nematodes in some of these. And so I wanted to explore the topic nematodes a little more. And Cynthia, can you tell us a little bit about what a nematode is for those of us who might be a little ignorant on the topic?

Cynthia Gleason: Sure Drew. Nematodes are small, unsegmented round worms. They’re basically worms without a backbone. And they’re found everywhere. They’re very abundant, and if you look at any sort of niche in the world, any sort of an environment, you can find nematodes. In fact, there was a recent report that said, for every human on Earth, there are 60 billion nematodes in the topsoil.

Drew Lyon: That’s a big number. [ Everyone laughs ]

Cynthia Gleason: Yes. So there’s a lot of nematodes out there.

Drew Lyon: Okay.

Cynthia Gleason: Most of them are going to be feeding on bacteria or fungi, but some can be parasites, parasites of humans. So for example, we have guinea worms and hook worms. There are entomopathogenic nematodes, and those are nematodes that can infect insects and be used as insect control. It’s really just a small percentage of nematodes that are plant parasitic. And they can feed off roots, stems, and leaves of various plants.

Drew Lyon: Okay. So that’s basically how they act as pathogens then? Just through their feeding?

Cynthia Gleason: Through feeding. Yeah. They have a specialized mouthpart that’s basically like a needle that can pierce plant cells and they feed off plants. And this makes the plant a bit sick. The plant, if you look above-ground, you’ll see it may be wilted, stunted growth, chlorotic or yellow leaves. So the plants get sick from these nematodes feeding off their roots.

Drew Lyon: Okay. And so there’s all these different kinds of nematodes out there. Which ones are problematic on wheat or small grains.

Cynthia Gleason: Probably, the most problematic would fall into three groups. We have the root lesion nematodes. Then we have cereal cyst nematodes. And there’re several species of cereal cyst nematodes in the region that may be problematic. And then lastly there are root-knot nematodes. But root-knot nematodes are not typically that common in non-irrigated soils.

Drew Lyon: Okay. So what’s the difference between a cyst nematode and knot nematode, and what was the first nematode? [ Everyone laughs ]

Cynthia Gleason: Right. A root lesion nematodes.

Drew Lyon: Yeah. How do you tell those apart or what are the differences between them?

Cynthia Gleason: Well the root lesion nematode gets its name because it feeds on roots and causes the formation of lesions or the roots to die back. And so they will migrate into the roots and feed and travel around and cause a lot of destruction. The cereal cyst nematode and root-knot nematodes they enter the roots and will feed, and they just sit there and feed and get fat. [ Laughter ]And they will basically cause the plant to divert nutrients and water to the nematode, and that’s going to make the plant vigorous.

Drew Lyon: Okay. I know when I’ve gone out to try to diagnose some problem in the field, I’m usually called in because it’s a herbicide injury issue, and so I’m looking for those kinds of things. But sometimes when I can’t decide is that a herbicide, is that a fertility thing, kind of the fallback position is maybe it’s nematodes. Rachel, maybe you can speak a little bit about how you go about distinguishing or telling whether it really is nematodes because, as you said, they affect roots, so you tend to see your root systems a little messed up, but several things can do that. So how do you tell whether it’s nematodes?

Rachel Bomberger: Absolutely Drew. So one of the first things, if Cynthia or I ever get a call with the person saying they can see little things wiggling from their plants, we know right away that they’re not actually going to be a plant parasitic nematode because they are much too small. I mean, they are microscopic to the point where I need one of those really fancy compound microscopes to actually determine if it is a plant parasitic nematode because I look for, what Cynthia talked about, the stylet or needle-like mouth, kind of like how aphids and mites have a stylet-like mouth. That’s what I’m going to be looking to identify. So right off the bat, if that’s the call we get that people see wiggling, we know that it’s probably not at least a plant parasitic nematode. So with the nematodes often, as you said, we’re going see this vascular stress, so lack of resources going up to the plants, that’ll be kind of wimpy looking plant, chlorotic. They might be stunted or patchy, kind of like what we see with Rhizoctonia and Pythium, this is again why it’s important to make sure you have an accurate diagnosis because your management options are going to change as we’ll talk about. So those are the first things we look for again. One of the things we will look for is reduced vigor in the plants. You know, stunting, chlorotic, not producing as well, or sometimes missing. Again, it’ll look like Rhizoctonia or Pythium fairly. With cyst nematodes, you can potentially see the nematodes. They’ll form little bead-like structures on the roots. I mean, they’re very, very tiny, but if you have good eyes or have good glasses, you might be able to see them. They’ll start out white, but as they age, they’ll start fading into yellow or brown. And again that’ll be on the root system. With root-knot nematodes, we can see really odd swellings or knots — hence the name — giving the plant kind of a bunchy or just a really odd root appearance. So in the field one of the things we’ll look for again as you said, is this poor vigor, plants not doing well. They tend to be in a group, but they can also be scattered throughout the field. One of the symptoms that we’ll see will be the chlorosis that we see with drought, nitrogen deficiency, or again the root rot fungi. So with the root lesion nematode, we actually see them in a disease complex with the Rhizoctonia and the Pythium. So as Cynthia mentioned, they got their name, root lesion, because they actually cause the same lesions that we might see on the leaves or the stems, but actually on the roots. So they are these discolored, brown areas on the roots, but you have to have good, clean roots, a way to actually observe that close to see that. So this is definitely one of those things, if you suspect you have nematodes, you do want to confirm with lab testing.

Drew Lyon: If a grower suspects they might have nematodes, for a consultant, what do they send you? Do they send you the whole plant with the soil attached to the roots or do they actually take just a soil sample? Can you tell from a soil sample? What’s the proper procedure for obtaining a sample?

Rachel Bomberger: So I recommend if you’re seeing this kind of ambiguous decline symptoms in a field, I do suggest taking a whole plant sample including and probably focusing more on that root, so with that rhizospheric soil. That way we can examine and see if indeed there is evidence of either any of these three nematodes. What happens then is I will usually suggest that the person then go to a dedicated nematology lab because they will be able to provide soil counts, identify two species, as we’ll talk about that knowing the species will help you determine what cultivars, what management practices you’re going to use. But if you suspect stunted plants, a good place to start is with the diagnostic lab and then I will then refer you to a nematology lab if I think you need to get counts or further species level identification.

Drew Lyon: Okay. So you identify that this could be a problem or is a problem, what’s a farmer to do? How do we control these little guys. It sounds like they’re everywhere. So how do we get them under control so they’re at least not affecting the crop in a way that’s detrimental?

Rachel Bomberger: They are definitely everywhere. I will now be terrified of going to bed tonight thinking about the 16 billion nematodes that just me being alive means they’re in the soil. So thanks for that, Cynthia. There are some general management strategies for all three nematodes. A big one is these are going to be soil-based organisms. So we want to avoid moving soils from infested fields. Unfortunately, root lesion nematodes are everywhere. The amount of damage they cause is again kind of like Rhizoctonia and Pythium. But for our cyst and root-knot nematodes, I would really recommend being careful in how you move through your fields because you don’t want to infest a field that was free from these nematodes. So watch movement of soil on equipment, tools, and even boots. That’s a big one. We walk around. Humans like to move soil with them. Identification of nematode two species is very helpful, particularly in the case of cereal cyst nematode, as it helps us determine which variety should be planted. Different varieties have different levels of susceptibility to the two species — Cynthia, correct me if when I say these heterodera avenae and heterodera filipjevi.

Cynthia Gleason: Right. That sounds close enough.

Rachel Bomberger: Good enough? [ Laughter ]

Drew Lyon: Passes my test!

Rachel Bomberger: Thank you. Some of these Latin names get really funny. But knowing which one you have will help you figure out what variety is best for you. And we have this sort of information on the Small Grains website. In general, winter varieties will tolerate both root knot and cereal cyst varieties better than spring varieties because the wheat plant or cereal plants planted in the winter tend to have more time to actually get more of a root system down. And the larger the root system, you know, the more they can sacrifice a few roots to these different nematodes. But spring varieties tend to be trying to grow at the same time that these nematodes are becoming active. So they’re more susceptible to losing those roots at a critical time for growth. Again, much like a lot of our root rot pathogens, particularly fungi, reduction of plant stressors including soil compaction, pH, nutrient deficiency, and planting good, vigorous seed at a good time of year depending on where in Washington you’re planting, we want to encourage rapid growth. That will help us tolerate nematode infection. Now unfortunately, chemical fumigants are actually registered for use in small grains for any of the three nematodes, but the other thing is fumigants are unlikely to be very economical. So even if we get a label that allows us to use these fumigants, in a dryland cropping system, where wheat is going to be our cash crop, it’s not going to be profitable to actually fumigate your fields. Fumigation is a really labor-intensive process. They’re actually pretty harsh chemicals too. They tend to kill unselectively. So it’s kind of a hard one, so really focus on plant health and varieties. I know we do a lot of research here at the USDA-ARS on nematode resistance.

Drew Lyon: So are there — besides growing winter wheat instead of a spring wheat — are there differences amongst varieties and how they react to these nematodes, and is that information available say on the Wheat Variety Selection Tool or somewhere where they can get that information?

Rachel Bomberger: It is. The information on these difference varieties, again, this is where it becomes important to know which species particularly of the small grain cyst and then the root-knot nematodes, which species you have will dictate which variety, both winter and spring, that will do better. And yes, they are available on the website as well as P&W handbook series.

Drew Lyon: Okay, and the website would be the wheat and small grains website, smallgrains.wsu.edu.

Rachel Bomberger: Yep, that’s the one.

Drew Lyon: All right. So Cynthia, can you tell me a little bit — I’m a little intrigued about what a molecular nematologist spends their time doing. Can you tell us a little bit about what you focus on in your research program here at WSU?

Cynthia Gleason: Alright [ Laughter ] Yes, sure. So my research focus is looking at how nematodes communicate with plants. How they are able to successfully establish infections in plants, and how the plants are responding to these nematode infections. But I’m looking at it at a molecular level. So the genes in the plants and the genes in the nematodes that change when the nematodes infect.

Drew Lyon: Interesting. And what crops do you mainly work in?

Cynthia Gleason: I mainly work in potato.

Drew Lyon: Okay.

Cynthia Gleason: Yea. We’re interested in seeing how potato is so susceptible to root knot nematodes. If we can understand susceptibility, we may be able to modify the susceptible response into resistance.

Drew Lyon: Okay. So you think the potato is sending some kind of signal that the nematodes are picking up on or visa versa?

Cynthia Gleason: I definitely think the nematode is being attracted to something in the potato. They go right for a potato roots. And then they enter the potato root or the tuber and they’re very successful at establishing themselves.

Drew Lyon: That stuff is fascinating to me. [laughter] I don’t understand it but it’s fascinating. Well thank you both for joining me today for this episode of the WSU Wheat Beat podcast.

Rachel Bomberger: Thanks Drew.

Cynthia Gleason: Yeah, thank you.

[ Music ]

Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcasting app. If you have questions or topics, you’d like to hear on future episodes please email me at drew.lyon — that’s lyon@wsu.edu –(drew.lyon@wsu.edu). You can find us online at smallgrains.wsu.edu and on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human and Natural Resource Sciences at Washington State University. I’m Drew Lyon, we’ll see you next time.