Exploring the Evolution of Cheatgrass with Dr. Ian Burke

Podcast: Play in new window | Download

Subscribe on iTunes | Android | Stitcher | SoundCloud | Spotify | RSS feed

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 from 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 podcast app and leave us a review so others can find the show too.

[MUSIC]

My guest today is Dr. Ian Burke. Ian is the R.J. Cook Endowed Chair of Wheat Research and a professor of weed science at Washington State University. Ian started working in weed science in 1999 and joined the faculty at WSU in 2006. His research program is focused on basic aspects of weed biology and ecology with the goal of integrating such information into practical and economical methods of managing weeds in the environment.

Hello, Ian.

Dr. Ian Burke: Hello, Drew. So, I think this is your 13th episode, and we’ve talked about a lot of different things over those conversations, but today I kind of wanted to focus in on downy brome or cheatgrass. It’s a weed that’s everywhere out there in the winter wheat production areas, and it was there when I came in 2012 and it’s still there. But, you’ve done a lot of work on it and have learned a lot of different things, so I was thinking we might just take a deep dive into some of the more basic research you’ve done and then maybe expand it into how those that basic research might relate to applied management practices.

So, what would you like to start with? I know you’ve looked at a number of things, genetics and the like, that maybe doesn’t get into some of your Extension talks that I think maybe our listeners would be interested to know just how much work you’re doing on this species.

Dr. Ian Burke: Okay, you’ve given me wide latitude here, and lucky number 13, I guess.

So, cheatgrass, we joke in my lab a lot about cheatgrass because I can put a graduate student or a technician in a truck and pick some random point anywhere in the PNW and they can go out to that point and they will find cheatgrass. It’s endemic. It’s literally everywhere. And we’ve always really struggled. And historically, you know, that’s been true since the 1930s. We’ve had a cheatgrass problem for nearly as long as we’ve grown wheat here.

And, you know, at first, if you look at in the history books, we did a lot of tillage to manage that. And then, we got an array of different herbicides over the years. You know, first, I think the first really effective one was metribuzin. We’ve experimented with atrazine. Then we got a lot of group two herbicides, we got sort of in sequence: Outrider, Olympus, Osprey. Oh, geez. PowerFlex. And then, in amongst that was Beyond–the Beyond system, the Clearfield system, and now we’ve got the CoAXium system, and in each case, cheatgrass has managed to figure out a way to overcome everything we’ve thrown at it, right?

And so, it was one of the high priority topic weeds very early in my programs. We got a very large grant—the REACCH Project was funded back in 2011 and I hired one of my first graduate students, Nevin Lawrence, who’s now on faculty in Nebraska, to look into this weed. And so, we had we had to start somewhere. So, like I said, we put him in a truck and we made 100 and some points, and he went to every one of those points and collected some cheatgrass from each one of those spots all across in the inland PNW–all the way to Ellensburg, all the way down into Oregon, east into Idaho, all the way up on Highway 2, up in Douglas County, and even up into Omak.

And, that first study was pretty eye opening. So, we planted all that germplasm out into a common garden and then watched it grow. That’s, I mean, there’s no really other good way to kind of put your finger on what’s going on other than to have this really wide collection you made and then grow all in one spot.

And what we saw was there’s clear differentiation in flowering time. So, everything we collected from what I would call the southern part of the PNW region–you know, the northern tier of Oregon and anywhere along the Columbia and Snake Rivers, particularly the county south of the Snake River–that flowered earliest. And anything along Highway 2 flowered much later, often three or four weeks later.

And so, when you dig into what controls that genetically, there’s an array of genes that control flowering time. So, there’s vernalization and then there’s several genes that control–or that trigger flowering time based on temperature. And what we realized when–we found one, we found the vernalization gene, VPN1 is what they call it, and could see clear differentiation and expression in this variable germplasm we were looking at. And we realized, okay, so this is adaptively significant. The cheatgrass grown on Highway 2, you know, adaptively shouldn’t flower early because it would get killed by frost. And the cheatgrass growing down in Oregon, well, there’s no real frost, and so it actually has a better chance of succeeding if it flowers earlier when there’s more moisture. Right?

So, that opened up the floodgates of ideas, right? And so, even at that point, our ability to ask really sort of simple genetic questions was really difficult. It’s an obligate-selfing species. So, you know, I’m always sort of envious of the plant breeders you’re going to talk to, I guess, because they can make crosses and they can make those crosses based on this variation that they see, and then they can explore that and look at the variation in the progeny and understand what’s controlling that gene, or that trait. They might be able to sequence the trait and actually be able to understand how and track it in some way. So, we really can’t do that with cheatgrass because we can’t self it. We can’t make a cross.

So, we started looking at dormancy traits next. Amber Hauvermale did a really great job trying, you know, documenting how cheatgrass has adapted to our wheat fallow systems. So, this is almost as fascinating as flowering times. So, we have cheatgrass that has what we call an extended afterripening requirement, and for whatever reason, it appears to have higher concentrations of abscisic acid just as that seed falls off the plant, so it’s able to put just a little bit more abscisic acid and that enforces dormancy.

Drew Lyon: So, for our listeners, you might want to explain what afterripening is.

Dr. Ian Burke: Yeah. So, afterripening is a unique dormancy mechanism in grasses. So, the seed doesn’t shed fully ready to germinate. It’s not completely formed and over the next few months sitting in, you know, warm temperatures on the soil surface, it has time to mature. And what Amber found was that the higher levels of abscisic acid actually made it so that that cheatgrass wouldn’t germinate in the fall, so in the fallow. So, it doesn’t–and we know that cheatgrass also germinates in the spring, but we’ve always–I’ve always been bothered by why the fallow didn’t really cause a significant drop in the populations we see here every other year in the wheat rotation. And that’s why, is because cheatgrass has evolved a mechanism to skip the fallow.

So, that made us think a little bit about using gibberellic acid. So, we had yet another graduate student, Madison Beaudoin, look into using gibberellic acid to overcome that dormancy mechanism. So, if you apply gibberellic acid, it antagonizes the abscisic acid that’s in the seed. And we can buy gibberellic acid. It’s a product used in many different uses in the ag space, but it’s not very stable in this soil system, so we’ve never really been able to use it effectively to manage weeds.

So, we were able to determine that, yes, there is an impact on using the gibberellic acid. It will stimulate germination in the dormant cheatgrass, but it doesn’t work very effectively in fields, like it’s just not reliable enough for us to really weaponize.

And then more recently here, I’ve had two pretty exceptional employees. I had first, Sam Revolinski, he worked with Jeff Maughan and Craig Coleman down at Brigham Young University to develop a genome. So, we now have a genome for cheatgrass. And, we identified an array of additional genes associated with flowering time as part of Sam’s project. I don’t know that we’ve really worked to understand it in the same way we understand sort of the very simplistic vernalization work that Nevin did; we haven’t quite weaponized it in that way or parsed it in that way yet.

And then, Shahbaz Ahmed’s here in my lab now as a postdoc and he has nearly succeeded in developing a transformation protocol. So, we’re on the cusp of having a pretty extraordinary little system to silence genes, and we have the genome now, so we know which genes maybe to go try.

Drew Lyon: And maybe explain when you say we have a genome, explain what that means.

Dr. Ian Burke: Yeah. So, I mean we have a–it’s an annotated sequence for cheatgrass. So, many of the more common plant species and, like, you know, all the crop species typically have an available genome. And so, we have the entirety of the genetic material in the plant fully sequenced, and then, by comparative analysis, you can identify genes in that genome that would be similar to others.

And what we found is it’s very similar to barley. So, a lot of the barley genes are found in cheatgrass. It’s the same seven chromosomes. It still makes us kind of chuckle.

So, we have all this genomic information, but there’s no real way to utilize it unless we can selectively turn off one or more of the genes to understand how they function. So, you turn one off and you watch it grow, and you see how it how that affects flowering time, for example. And so, that’s really the vision for the next few years is to think critically about what other genes do we need to know and understand and how can we utilize that those tools to peel apart this onion of cheatgrass problem in a way that we can make some of that information actionable to farmers?

Drew Lyon: Okay. As you were speaking I was thinking, you know, when I give Extension talks, I often talk about herbicide resistance and how our weeds evolve to do it. But your discussion tells me they evolve for a lot of other traits as well. It’s not just herbicide resistance, it’s flowering time, it’s all these other things. And so, that’s kind of what keeps a species like cheatgrass usually a step ahead of us is that it’s just whatever we throw at it, it’s figuring out a way to survive, and it seems to be very rather adaptive that way.

Dr. Ian Burke: One of the side projects Sam did was Amber had gone out and collected a number of–she collected from a number of different fields, but she collected a lot of different cheatgrass plants from within each individual field. So, I think she went to like 7 or 8 different farmer fields across the inland PNW and collected a lot of different material from a wide area in that individual field.

And Sam used that and what he found was that certain fields have a lot of genetic diversity. And then there are other fields that have essentially none, so all the cheatgrass is the same. And if you remember, I’ve said it now a few times, it’s a selfing species, so every seed that falls off an individual cheatgrass is essentially a duplicate of that mother plant. And so, in order for there to be diversity, genetic diversity, there has to be a lot of different kinds of mother plants from all over. And so, that told us a lot about potentially what we might be dealing with here is that there’s just a lot of communication occurring, a lot of seed transport between fields to enforce that variation that we’re seeing.

And so, one of the other projects we’re interested in doing is understanding how different kinds of field scale implements that farmers use move those cheatgrass seed, and because we have the genetic tools, we can actually go in and go what is the consequence after five years, after ten years for cleaning your implements or not for the genetic variation we see. And if we have lower genetic variation, is that good? Can we actually use that to manage the cheatgrass in some way? So, there’s still a lot of work to do, but it’s been exciting to kind of tease apart this problem.

Drew Lyon: And you’ve really, like I said, taking a deep dive into the species. I wonder, [has] anything come out of that yet from a management standpoint, do you think? You just mentioned the moving of seed, maybe that’s a bigger factor than we’ve played up in our management recommendations? You can go further on that one or if there’s some other things that have come out from this research that you think farmers could use as they try to manage this very difficult weed.

Dr. Ian Burke: You know, I think one of the basic lessons we learned was that cheatgrass vernalizes a seed–and that’s something that Dan Ball did a pretty good job at documenting–but we have, you know, reinforced that with our research. So, anything that germinates in the spring is likely going to set seed. And so, the real question is how late can it germinate and make seed? And my overall sense is later than we think.

We did it–we planted a common garden in Pullman and I think we planted it in like mid-April, and almost all of that material was able to successfully produce a viable seed. So, farmers who are thinking about spring wheat as a rotation to clean up some of these cheatgrass problems, then they actually have to really think critically about how late they plant. That’s a really, really important decision and it could be as late as early May. Or maybe spring wheat is not viewed as a viable solution for breaking the seed bank on cheatgrass. We’ve got to have something planted even later. And so, I think that’s probably, to me, the most important lesson we’ve learned thus far.

You know, some of this genetic and genomic work has a return-on-investment window that’s a lot longer. But, we’re always trying to figure out a way to take what we’re learning in real time and turn it around as a lesson.

Drew Lyon: Yeah. And I think it’s critical, right? I think having the genome, like you said, and now being able to play with some things, I’m pretty certain that will yield practical suggestions for management in the future, so I think it’s important work.

I think maybe we’ll leave it there, Ian. Continue this great work. We can put your contact information in the show notes, but is there someplace somebody can go to see the work that’s being done in your lab? Do you have a website or something?

Dr. Ian Burke: A lot of this work appears in different places, both on the old REACCH website, reacchpna.org, I think is the website. And then the pnwhri.org website is also a resource that we’re beginning to build out. And of course, much of this material also appears on the Small Grains website, although some of the fundamental work that we’re talking about here hasn’t quite made it into an Extension bulletin. Yeah, and I’m always open to questions from anyone anytime.

Drew Lyon: Okay. We’ll get that information in our show notes.

Ian, thanks for being my guest today and all the other times you’ve been my guest. I’ve really enjoyed our conversations.

Dr. Ian Burke: Appreciate the opportunity, Drew. Thank you.

Drew Lyon:

[MUSIC]

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 podcast 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 [X] @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.

[MUSIC]

---

The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.