The Coming and Going of Soilborne Wheat Mosaic Virus with Dr. Christina Hagerty

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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.

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My guest today is Dr. Christina Hagerty. Christina is an associate professor of plant pathology at Oregon State University’s Columbia Basin Agricultural Research Center. She is the first female chair of the National Wheat Improvement Committee and the Oregon Wheat Faculty Scholar. Christina manages the Pendleton Cereal Pathology Lab, which is focused on serving the producers and stakeholders of high-quality Oregon wheat.

Her goal is to conduct relevant, practical, and applied research on the biology and control of plant pathogenic fungi, viruses, and nematodes that limit yield of dryland wheat production in the Inland Pacific Northwest.

Hello, Christina.

Dr. Christina Hagerty: Hi, Dr. Lyon. Thanks so much for having me today.

Drew Lyon: Yeah, thanks for coming on. I wanted to talk to you a bit about soilborne wheat mosaic virus. It’s an issue that’s starting to spread out a little bit. We’ve always had a little bit down around Walla Walla and down in your area, but we’re starting to find it in other places, so I thought I’d visit with you about that. I wonder if you can give us an overview of soilborne wheat mosaic virus in the PNW?

Dr. Christina Hagerty: Absolutely. So, it was first discovered, like you mentioned, in that Walla Walla region in 2008, and also in the Hermiston irrigated region. And there are three gentlemen responsible for making that discovery: Dr. Tim Murray from WSU, Dr. Dick Smiley at Oregon State University, and also Phil Hamm at the Hermiston station. So, when that discovery was made, you know, over a decade ago now, it was this small focus of infection where there was adequate moisture for the disease cycle of soilborne wheat mosaic virus to really–was adequate for it to really take off. But we saw the distribution of soilborne wheat mosaic virus stay pretty limited to that area for many years.

Drew Lyon: Okay. So, as I mentioned, we’re starting to see it, find it in other places. So how does it spread?

Dr. Christina Hagerty: So, yeah, it is slowly expanding in acreage over the years. And the trickiest thing about soilborne wheat mosaic virus is it can spread any way you can imagine infested soil moving in our landscape. So, you know, that might be commodities moving in and out of the irrigated region, so this would include potatoes and onions that tend to carry a lot of soil with them as the trucks are moving around.

You know, the virus is extremely small, so thinking about it moving on dust in windstorms is not out of the possibility, although no one’s ever specifically confirmed that. And then, as we’re moving through our plots, we often see these gigantic herds of elk and deer that come down off the Blue Mountains and move through the trials and we can assume that they’re taking soil with them as they graze other wheat fields, from an infested field to a healthy field. So, that would be sort of more–ways that the virus can move in the landscape outside of our control.

For a long time, we had thought that equipment sharing and equipment transfer from field to field was a pretty big culprit for spreading mosaic virus. And while that may be true, thinking about sanitizing a commercial piece of equipment from field to field is not necessarily a practical consideration that a grower could do, especially when they’re up against these big time crunches at times of seeding, spraying. Basically, anything in agriculture tends to be quite time sensitive.

So, we’re very careful to sanitize our equipment when we do mosaic virus research, but that’s because my drill is five feet wide, so is my tractor and combine. But for a grower, sanitation of equipment just might not be in the cards.

Drew Lyon: Okay. When you say sanitize equipment, what are you meaning? Is it just washing it down, sweeping it out, blowing? What goes into sanitizing to do a good job?

Dr. Christina Hagerty: Yeah. So, typically a true sanitization effort might include a hot water power wash or a bleach scrub down. But at a minimum, it would include knocking off large pieces of dirt that that collect on agricultural equipment. But in our case, that would typically be a power wash situation.

Drew Lyon: Okay. So, one of the traits of this virus is it tends to be visible early in the spring when things are cool and then the symptoms seem to go away as things warm up. So, because that symptomology kind of disappears, is there a yield loss with this disease?

Dr. Christina Hagerty: Yeah. Great question. And this is a really big focus of our education in recent years. And to help explain the answer I’m going to give a very brief overview on the disease cycle.

So, soilborne wheat mosaic virus is transmitted by a soilborne fungal-like organism and that infection of the wheat plant typically occurs in late fall-early winter when adequate soil moisture is present. But, we don’t see symptom expression until plants are starting to break dormancy and really start to put on foliage. But then as soon as daytime temperatures hit about 70 degrees, that virus replication will stop and the plant essentially grows out of the symptomology—the chlorosis, mosaic modeling on the leaf tissue. So, for many, many years, it was thought that there wasn’t any significant yield loss associated with mosaic virus because the symptomology really just disappeared and the plants grew out of it over time.

But in some of our early work on this disease, our work indicates about a 40% yield penalty, even considering that plants are symptom free at the end of the season. So, still a very significant yield loss, even though we can’t see it or tell it’s even there, [from] flag leaf and then into harvest.

Drew Lyon: Okay, that’s a pretty significant hit on your yield if you happen to suffer that.

Dr. Christina Hagerty: It is, yeah. I’ll just add something there. It is a significant yield loss of 40%, but the other factor here is in dryland environments, the distribution of the disease in a given field tends to be pretty patchy. So, it would be rare to see 40% yield loss across an entire field in dryland conditions. What a grower would need to do to get a handle or an estimate on yield loss would be just estimate the size of patches that were covered by the disease and then just take 40% from those patches.

But, in irrigated conditions, there’s adequate soil moisture for uniform infection across an entire circle, so in that case, we would see a potential 40% yield hit across the whole pivot.

Drew Lyon: Okay. So, in a dryland situation that patchiness would tend to be in, what, maybe lower, wetter areas? Is that true?

Dr. Christina Hagerty: That is typically true, but plant pathogens are tricky and sometimes as water is sheeting off of a pretty steep slope and we have soil textures that are non-homogenous across a field, you can see all kinds of patterns that may not exactly make sense. But, a general rule of thumb is it’s going to follow those wetter patches and drainage slopes.

Drew Lyon: Okay, so how does a grower go about avoiding yield loss?

Dr. Christina Hagerty: So, that’s another tricky part of this disease is once it’s established in the field and once we see symptoms, there’s not much of anything we can do in terms of a spray or a cultural management to avoid yield loss. So, where we go with that is our management goes to the next season and we typically tell the grower, “Alright, we’ve got mosaic virus this season.” Although there’s nothing we can do about it now, we use molecular tools to confirm that it is in fact mosaic virus, and then encourage them to note that in the field so that the next time that field goes to wheat, they can choose a resistant cultivar.

Drew Lyon: Okay. And are there cultivars out there that are more resistant than others?

Dr. Christina Hagerty: There sure are. Yeah. So, it’s a short list for now, but that list seems to grow every year or every other year as we all appreciate that the breeding process is very slow. But breeding for mosaic virus resistance remains an objective in most of our public and private breeding programs.

And we’re lucky that prior to the arrival of mosaic virus in the PNW, the gene for resistance was present pretty randomly throughout breeding material for the PNW. And that’s because there are other parts of the world and other parts of the United States that have been dealing with mosaic virus for quite some time. So, as germplasm gets exchanged as breeders do, the PNW programs have ended up with that gene in material that’s ready to go and can be intragressed over time into PNW-adapted material.

Drew Lyon: Okay, so even though it doesn’t impact a lot of acres or hasn’t impacted a lot of acres, the genetics is there and as we see acreage increase, there will be options, you think, for growers to find those varieties?

Dr. Christina Hagerty: Yeah. I’m hopeful that our breeders will continue to prioritize mosaic virus and we certainly continue to, you know, keep our finger on the pulse of what mosaic virus is doing in terms of expansion.

And, in terms of expression of mosaic virus in the PNW and in given fields, oftentimes soilborne diseases, they’ll follow an exponential curve growth. So, what that means is if you can visualize an exponential curve, that’s great, but if you can’t I can describe it. So, essentially you have something that limps along at a very low level over time and then what I like to call “the kaboom”, when that curve of that population really starts to take a steep upward rise in presence. And so, that’s why you may have a field that has looked great for the past 20 years and then all of a sudden, you have a pretty significant level of infection.

And, of course, mosaic virus, like any plant disease is not immune to the good old plant disease triangle. So, we do have to have the perfect environmental conditions in order for it to express, which comes and goes throughout the years–sometimes we’ve got a spring that’s just perfect for mosaic virus infection. Otherwise, not so much, and then mosaic virus sort of falls out of favor and is no longer top of mind for a grower. And, you know, they may even forget that a certain field has a high level of mosaic virus severity.

Drew Lyon: Okay. So, if a grower suspects they might have soilborne wheat mosaic virus, what should they do?

Dr. Christina Hagerty: That’s a great question and there are so many ways to answer this, but what I typically like to mention is that unfortunately, there’s no really adequate soil test to test for the presence or absence of mosaic virus. And that has to do with a lot of different factors, but mainly the factor of taking a soil sample for a pathogen like mosaic virus, it’s kind of like taking an eyedropper of a sample out of the whole ocean. You may get a representative sample and you may not. Subsampling a field can inspire false confidence or false pessimism if you sample in a non-representative location of the field.

So, really what we need to do is wait for symptom expression in the plant itself. And then once we have symptom expression, mosaic virus is a lookalike malady to many other things. [It] could be nutrient deficiency. It could be other diseases. So, something like ceph[alosporium] stripe is a really key lookalike to mosaic virus. And so, if you suspect it, grab a tissue sample and take it to your favorite plant clinic so they can utilize molecular tools, and that way you’ve got your diagnostics nailed.

Drew Lyon: Okay. That sounds like good advice. So, watch for the symptomology, go grab a plant sample, and get it to a pest diagnostic clinic either here in Washington or there in Oregon.

Dr. Christina Hagerty: Absolutely.

Drew Lyon: All right. Christina, thank you for coming on and discussing soilborne wheat mosaic virus with me. I know it’s gaining a little more attention here in Washington as we find it in a few more spots. And I think there’s been some spots located in Idaho as well, and down in northeast Oregon.

So, this information is important. We’ll make sure your contact information gets in the show notes so growers who might be interested in learning more can contact you if they have questions.

Dr. Christina Hagerty: Super. Thank you so much for having me. And, yeah, please reach out with any questions you might have.

Drew Lyon: Very good. Thank you again.

Drew Lyon:

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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.

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