In Defense of Biological Systems with Robert Linderman

Hi friends, this is John and this is the Regenerative Agriculture Podcast where we talk about agronomic science and cultural management practices that regenerate plant health, soil health, and ultimately also regenerate public health. Today I have a guest on the podcast that I've been wanting to have for some time. When I was introduced to him the first time or told about him the first time, I was told that this individual is the senior grandfather of mycorrhibral fungi research and developing disease suppressive soils and that very few people, fewer people know about him and deserve to know about him. So today I'm excited to have Dr. Robert Linderman from the USDA here from Corvallis, Oregon. Bob, thank you very much for agreeing to be here and sharing some of your knowledge and wisdom. I'd love to hear more about your story and background. How did you come to do all the research that you've done in developing disease suppressive soils and with mycorrhizal fungi associations? Tell us a little bit about your story and your background and how you came to this spot.

Well, thank you very much John. I appreciate the opportunity. My history goes back a long ways, as you already know. I started out as a zoologist, a pre med student. I went to Fresno State College and became interested in plants. Actually along the way went to graduate school, eventually went to graduate school at UC Berkeley and worked with some world renowned people on diseases and pathogens. And in 1967 I graduated from there and went to the USDA ARS Research Facility in Beltsfield, Maryland. And there were people there that I got to know, but one of them happened to be a person interested in mycorrhizal fungi. And I got to thinking about mycorrhizal fungi in a broader context and kind of became a student of that at that time. But then I was transferred to Corvallis, Oregon where there were other world renowned researchers working on mycorrhizal fungi. And I was still a student of that subject. And it just kind of went from there. I began to study it and say, well, this is one of the most important components of the the rhizosphere of plants that would affect plant diseases, especially root diseases. And it kind of went from there. I began to study all the interactions that occur in that zone next to the roots and became interested in the concept of the potential of biological control to control those pathogens in that zone right next to the roots, around the roots. So the rest of my career kind of related to that and I addressed specific pathogens on nursery Crops, but always had the idea that some of those pathogens could be controlled rather than with chemicals. They could be controlled with biological systems. It's a matter of how to develop and find the systems and make them work. And that's been kind of a struggle for, well, ever since. There's a certain reluctance to consider the concept of biological control by many growers because they already have their systems kind of worked out and they kind of know. And then there's a lot of chemicals that people can sell them that would address certain diseases. And so they kind of push aside the idea of biological control. Well, that's all changing in current times because they're more concerned about chemicals being used from both a standpoint of human health as well as damage and impact on the environment. There are a lot of companies that have kind of shifted a little bit into biological control, developing products, and there are a lot of biological control products out there. I think the real problem is those people that might want to consider biological control really don't know how to get started. And the key is try to, in my opinion, is not to necessarily try to change the whole biology of the soil, but to change the biology of the soil right next to the roots and on the roots. So that means prevent the disease before it ever happens. And that's kind of the thrust of everything that I am thinking now and things that I've done. And that includes mycorrhizal fungi, the organisms that associate with them, in part of a team effort to potentially suppress pathogens and enhance plant growth and health. And that's kind of where I am right now. I retired from the USDA in 2007, so I've been retired for almost 13 years. I'm a private consultant right now with nurseries working on these various things. We're talking about trying to have the nursery people be able to control diseases that they get. And as we talked the other day, the potential for field crops where transplants are being used is still part of the nursery industry. We could manage those populations on the roots of soil, of plants in the nursery, before they ever go to the field. And that's kind of a concept that we could explore further. And I'll stop talking there, and maybe we can go to some questions that you have.

Well, there's no shortage of questions that I have for you, that's for sure. So just some of the things that you've mentioned in your quick introduction, a number of pieces that you brought up that I wanted to dive a bit deeper on. But let's Perhaps start with the question of if you are a commercial grower and you have a desire to develop disease suppressive soils and to manage some of the pathogens that you have challenges with a given crop, how do you begin? Where's the start, where's the starting point? And how can you. There's also a lot of questions about the broad range of biocontrol products that are available, which are effective, which are not effective. We know it's very context dependent. So how do you make the decisions about what to choose and where do you begin?

Well, let's just say you're a grower with some specific disease problem. You have to consider the products that are out there available to you right now that would address those pathogens, that specific disease. I'll just look at your list and think of some of the kinds of things like Fusarium or let's go to Rhizoctonia. How could you control Rhizoctonia? You have to ask the question, how and when does Rhizoctonia get in to cause the disease? Is it present in the field soil that you're going to plant into? And if so, it would be a good idea to be able to take a product where the label says this organism or series of organisms works to control Rhizoctonia. And then it's a matter of delivering that product to the site where it needs to be to work in a timely way, that is before the pathogen ever gets to the root. So that means pre inoculation or that means inoculating transplant or inoculating a bulb, an onion bulb, so that there's already a population. It's like immunizing the plant before it ever gets exposed to the pathogen. So any grower can then look at the label and sometimes the labels are going to be maybe inclusive of the pathogen that you're considering. And that doesn't necessarily mean that it's going to work on the stream of the pathogen that you are faced with in your soil. So there's that kind of specificity that can be a problem. So the real way to test that, and there are not many people doing this kind of thing, would be to isolate the pathogen that you have in your field and test it against the product that you're going to be using. You can do that in a petri dish test or you can develop some other kind of a plant bioassay that simulates what would happen in the field. I'll take an example. There's a product called Triathlon. The label says it will work against Rhizoctonium, fusarium, Phytophthora pythium, about five different pathogens. The question would be whether or not that product has enough of whatever works against Rhizoctonia to actually do the job. If you load the plant system up in advance of being exposed to the Rhizoctonia, then you have the best chance of succeeding. And that's where most growers are not quite in tune to the timing of the whole thing and where to put the material and when. And sometimes it doesn't do any good to add the product to a big volume because the population doesn't maintain itself in the right place at the right time to do the suppression of the pathogen. So the grower needs to consider all those kinds of things when developing a product. Maybe there is no product that controls the pathogen that you're concerned with. For example, I'm not really sure Macrophormina is the pathogen that causes charcoal rot. Are there products out there already that would be addressing that pathogen? Actually, I could look it up, but I don't really know the answer right now. But let's say there isn't one. There are ways. And this is back to the paper I just mentioned earlier to you, John, about strategies for finding and characterizing biocontrol agents. You could go to the field and look for examples where somehow the pathogen didn't do its job and there's escapes. You may be able to isolate a pathogen and its antagonist from that field and then develop that. Well, somebody has to do that commercially in order for you to do it. The farmer's not going to be able to do it themselves. That ends up being a problem. And that's kind of where we are right now. We may not have the specifics they're needed for that particular strain of the pathogen in that specific field at that point. That's where some farmers will say, it's too complicated, it's too much trouble, and I don't have anybody to go to to help find that organism and develop it. And so they go to chemicals as the best choice they have, or some product that they might try to see if it works.

Bob, you've hinted that timing of product application is really important and that my understanding is that it needs to be applied before the potential pathogen actually produce infection. Is it necessary always to apply materials at planting or even before planting in order to produce the control effect that we're looking for?

Well, for sure, and they're really good examples of why this is really essential. But in almost every case that I can think of, to get the protection there before the pathogen gets there should be the best thing, no matter what. The question is, depending how the farmer farms and whether seeding or transplanting or planting bulbs or whatever to treat that material, where the infection is going to happen. To have something there waiting for the pathogen when it tries to get into the plant is the best chance. It's like immunizing a child for infections that might come. You build up some kind of resistance, and the resistance is in biological form. If you wait until the pathogen already has started, it's pretty hard to chase it down. It's like closing the gate after the cows are out. It's just a hard thing to do and maybe totally successful. And that's, in fact, the outcome for many people. I tried that material, but it didn't work. Well, when did you put it on or where did you put it? I can give you an example of mycorrhizal fungi, for example. Did he put it on the root system or where the roots would run into it? No, I put the fungus in a candy spreader and spread it over the field on the top. Well, it needed to be down where the roots were. So if you failed, that's good reason for it. You didn't put it where it needed to be in a timely way. And the same would be true with any biocontrol agents. And of course, there are ways of building up. This is a point to make, too. Almost all soils have some antagonistic organisms to most pathogens. They're just there in too low a population to do what they need to do in a timely and effective way. But if you can find them, build them up to a higher population so they dominate the site that infections are going to occur in, then you have a good chance. The disease called crown gall is a bacterium. You must use the biocontrol agent to protect the wounds that that pathogen gets in. That's the normal way it gets in. And if you don't protect the wounds, then you get crown gall. It's as simple as that. And so you just have to find the organism, put it in the right place at the right time to prevent the disease. The key for me in all of these things is prevention. Prevent the disease before it ever happens. And that's the same concept with immunization. You prevent the disease from occurring.

Bob, so far we've been having this conversation in the context or in framing it around the use of commercial products, which are valuable and necessary tools, and more of Them are being developed and going through the registration process all the time. What are the cultural management strategies or cultural management practices that growers can use to enhance the development of disease suppressive organisms in their soil profiles and shift their soil profile from one that favors the expression of pathogens to one that suppresses it?

Well, there are certain substrates that you can add to soil that will at least increase the biological diversity, assuming that the biology of the soil, there are some components there to there that could be effective in the biocontrol process. If you build them up in population. You put some organic matter, for example, in the soil, or chitin in the soil, you build up specific organisms that like that substrate, like the actinomycetes, like chitin, because they can produce an enzyme that breaks it down. So that population of organisms will build up specifically or preferentially on a chitin substrate. Other organisms don't like chitin so much. They aren't going to build up very much. So you can kind of shift the population in your favor in that particular case. But adding organic matter in general will increase the microbial diversity of the soil and there'll be a greater population of organisms that could suppress the pathogen, but they're also there competing with everything else, like that substrate that compost organic matter. It's difficult to favor the biocontrol agents that you want. With a general amendment like that. You can kind of get to the idea that if you have a greater diversity and then you have some selective pressure that allows those organisms that you want to be recruited from the population and given preferential treatment, then you've shifted the population in favor of the organisms that you want. One of the things that does this, and you've read the paper I sent you on the mycorrhiza sphere, but when you have mycorrhizae on a plant, they help recruit antagonistic organisms from the background soil so that the population of antagonists in the presence of mycorrhizae is greater than if you don't have mycorrhizae. So that's one way of preferentially shifting the population to something that you want. A team of organisms that some of which are antagonistic to a range of pathogens. And what builds up against one pathogen is not necessarily the ones that build up against another pathogen, but the concept of mycorrhizal association stimulating antagonistic organisms in general, thereby increasing the antagonistic potential against a range of soil borne pathogens is very good.

We have growers that we're working with for producing very high Value crops. And as fumigation becomes less and less of a viable commercial option, many people are asking the question what is the fastest route that we can take? There's no holds barred. Budget is not a limitation. We're willing to do whatever it takes to develop soils that can suppress these organisms. What's the pathway that you would advise them to use? What's the combination of cultural management practices and products that they should use to achieve the optimal results? And we can use Caesareum in soils as an example, or fusarium in strawberries or macrofamina.

I'm not working specifically with those, but I think you have to. Even if you were to choose a biological product and you add that in a system where there's a population potential to be built up by some organic substrate, that is, you could add organisms and favor them by having some food material there to build up a population of them in advance of planting, that would be the key. And of course, the other thing you and I have talked before about, and you've written a lot about improving soil health, that's one way you can increase the microbial diversity and therefore the soil health. But if you wanted to really increase the population next to the root system where the pathogen is about to invade, then you probably need to inoculate the propagule of the plant or put the organism right where the roots of that plant will come in contact with it very quickly. That could be a drench of organisms, some product, for example, right into the system where the plant is going to have to grow, where the roots will develop if they get associated with the root system. Wherever the root system goes, the organisms will follow it. They'll stay with it unless you do something that's pretty drastic. And sometimes those treatments are drastic. They may also be trying for biological control, but give up on that or decide to add some chemicals that may put the whole system on hold or suppress it. I'm not sure I got to the right answer there. What you were specifically asking that you have talked a lot in your blog about the fertility and the kinds of changes that would occur with different kinds of fertility. There are surely examples where that kind of approach has shifted the population in such a way that antagonists are favored. There's an example on wheat. Take all. For example, here in Oregon, Bob Howlison many years ago found out that potassium chloride could be added and shift the population toward antagonistic pseudomonads. There are other people that have done the same kind of thing with seed meals and things like that. And you increase the Antagonistic population, then you get less disease. What will be happening specifically with macro Fermina on strawberries or any other crop? I'm not even sure, I don't know the answer to that. But there could be certain cover crops that might favor the buildup antagonist. And you need to be able to measure the change in antagonistic potential as a result of whatever you did, whether it was plant a different cover crop. There are examples where certain crops favor the buildup of antagonists against the pathogen that was going to occur on the next plant. Those kinds of things are probably known, but not necessarily known by the farmers that are going to try to practice it unless their, their fathers or grandfathers told them this is the right way to do it. Surely many of those stories out there.

There are so many of those stories out there. And this is exactly, exactly the type of conversation that I've been hoping to have with people and to draw out. Because the story, the example you just shared of using potassium chloride to increase the antagonists for a pickle disease in wheat, there are, there are so many cultural management practices that are known collectively by people in agriculture and horticulture to how to control a specific disease organism in a specific context. But with cultural management practice, I would consider this a cultural management practice. Using tools, using specific forms of nutrients and specific types of products to shift the soil microbial profile. Is is knowledge that is out there, but it's not common knowledge. It's become. Well, vested interests, I believe have, and just human nature. It's been easy to just buy a product in a jug, as in a fungicide or something like that, and go fix the problem. In reality, we have the collective knowledge amongst us to prevent a lot of these problems from showing up in the first place. If only it were more widely known.

Well, all these things are kind of specific examples. And so it's really difficult to find one common denominator that would apply to many systems. That is what cover crop would build up antagonist to a specific pathogen. Whatever the problem is. You mentioned the other day a Phytophthora problem on peppers, I guess it was. You have to know what the strain of the pathogen is and what that soil history is. And I don't think there's anybody collected all the information on any specific crop as to what cover crop you should be used to prevent such and such a disease. It's known in some cases, but not a lot. And frankly, the emphasis by research people and farmers, agronomists, horticulturists, has not been to find those organisms and develop that strategy. That's a protocol for growing your crop. Unfortunately, I think the information could be there, but it's buried a little bit in all kinds of literature or no literature. I can tell you the potassium chloride story, for example, on take all, was not published in a refereed journal paper. It was something that was either an abstract or some local thing. And I happened to hear about it because I knew Bob Powelson. But those kinds of things are sort of buried in the literature, and that's a really unfortunate kind of thing. In my own case, too, I published papers that are buried in referee journals, but the farmer never sees them. How do you get that material translated and put into a language that somebody can read easily and say, this is how I'm going to approach it, or talk to somebody who will guide them through that? And I'm not sure there are that many people out there that would be in that category.

What are some examples of some of the papers that you've written and that you think farmers would really value knowing about, but that aren't widely known?

That's a hard question, because I kind of know what the papers are. I went through a process fairly recently, since I'd worked on using onions as a test organism for mycorrhizal fungi for many papers. I decided those papers were all buried in the scientific literature. Maybe I should collect them and summarize some of those papers and put it in the journal called Onion World, where the farmers would actually read it, hopefully. Well, I published that paper and it went into Onion World, but then I have no idea whether the onion growers actually read it. And that's this. I know that this is where you might have come from too, because you were involved in this process we're going through right now, plus your blog, to try and translate and transmit some of that information to growers who need it right now. They need to have it translated. They need to have it put into perspective that they can understand and try to apply. And I don't think there's a lot of that kind of thing. There's not enough of that happening.

Well, it certainly. There's many days for me when it appears to be an almost overwhelming task, because when you start getting into some of these papers, I become extremely excited by the implications of connecting the dots, what a piece of research or a certain paper means when we connect it to the rest of the knowledge base that is out there. But then you start following the bibliography, and all of a sudden you discover that this paper cites an Additional hundred other papers, of which 20 appear to be really exceptional. And it's just an ever expanding list with no end.

Well, I'm hearing what you say and I totally agree. And you asked earlier what paper, even ones that I published that I could point to that might be something that would tease growers into thinking about biological control systems. And the paper I just mentioned on strategies for detecting and characterizing biocontrol systems for soil borne pathogens is probably one that, that would maybe get growers if they read that paper to look down there and say, oh, here's an example, I've got crown dahl or I've got take all, or I've got root rod of beans. And there's some grower people that we referred to in that paper that did such and such. They grew certain crops before beans. Well, I've never done that, so maybe that's something to try. But it gets them thinking about how they can figure out what parts and what strategy they need to use for their specific crop. And of course there are farmers that grow different crops. I mean, in your area a lot of corn and soybeans are grown, but there are also all kinds of vegetable crops and pumpkins and on and on. Then you have to consider the specifics of the pathogen. And that's where a lot of people will get off because they're talking to agronomists and horticulturists maybe and not necessarily working with a pathologist that can deliver some specifics about the pathogen and what they need to consider. There are pathologists that are out there in your areas. Don Huber is a really good example of somebody who knows those crops and knows those systems. You have to talk to them. But there's a few Don Hubers out there.

I want to say that there are very few people who take a systemic approach. And I'm coming to realize that there are many people actually who do take a very systemic approach to trying to understand these problems. But they are still in the great minority. It's still very easy. One of the challenges of the scientific method being brought into agriculture has been the easy method of doing research is to attempt to do single factor analysis, identify a specific factor, change it and observe what happens. Of course, agricultural ecosystems are extraordinarily multifactorial. There's so many different factors that all work together and collaborate in these systems. Things that we don't even fully understand yet. And within that context, our conversation to some degree, we've been talking a little bit about systems, we've been Talking about cultural management practices and products and so forth. But I'd love to hear a specific example. Let's say we're dealing with Phytophthora issues on a specific crop. What are all the different tools or combinations of tools that you could bring into a system to all try to have an influence on Phytophthora? We can supply specific products, we can grow cover crops in advance of the crop. What are some other things that we can do? And also parallel to that question is, are there combinations of products that we should consider trying? FOMO inoculants combined with bacterial inoculants combined with biosimilars and so forth. What is a true systemic approach to solving the issue rather than just taking a single factor point and shoot approach?

Let me point you to that paper we're talking about on strategies and refer you to the system called the Ashburner system in Australia. Phytophthora root rot on avocados. Ashburner was a farmer who knew he had Phytophthora and his neighbors had Phytophthora. And right next to his fields were the rainforest areas. And what was in the Phytophthora was there, but it didn't cause any disease. What was different about those two systems? And Ashburner decided he was going to bring that system into his orchard. So he started growing a cover crop of material called lab lab. And he didn't just chop it up and work it into the soil, he chopped it and laid it over and built up a thick layer around his trees. He added lime. The system is described in that paper, by the way. That's what I'm saying. The Ashburner basically brought his trees back into product by that whole system. Now he didn't understand or know all the other components that were in. He didn't know anything about mycorrhizal fungi which could have been involved. But these suppressive soils, he created suppressive soils. And the suppressiveness had to do with organisms that would suppress the development of zoospores of the pathogen. If the pathogen doesn't develop zoospores that swim to the roots and infect it, then you don't get root infection. Pretty soon you have enough roots that are healthy and being protected to sustain tree. And those trees came back to production and he went on his merry way. He did that whole system from that point on. And there are other people that have examples that I refer to in that paper where they've done this for years and years and they don't have bean root Rot, for example, or they don't have crown gall each case. You mentioned Phytophthora on pepper. What would have to be done to build up the antagonistic potential of that field over time? That could be a real problem because the grower may grow peppers one year and decide, well, okay, I had a lot of disease, I'm not going to grow peppers there anymore. So it's not like you have a sustained buildup like you would with take all decline, something systemic. And when you get down to the whole thing, with a few exceptions, most all the plants on the earth form mycorrhizae. Mycorrhizal fungi for me have become the key component. And we still don't have people inoculating with mycorrhizal fungi, even though they may be the orchestrator of really good things to come, including building up antagonistic potential, not only mentioning the increasing uptake of phosphorus and other nutrients, those kinds of things are what people talk about. But there's a whole shift in the biology of a plant internally and externally if you have mycorrhizal fungi, and that includes building up antagonists, nitrogen fixers, but not many people are studying it, so we don't really know all the things that could be happening as a result of forming mycorrhizae. And you have to do it early. It's again the same with the protection against pathogens. You have to get it there before or as early as you can. And that means how and when I can apply the organism or that product to get my razza established as early as possible, therefore benefit thereafter. We just don't have enough products and people doing that. You could be inoculating. And this is back to what do you inoculate? Well, in my case, with cut, I can inoculate cuttings. I want to sanitize the cuttings and then inoculate them with beneficial organisms, like antagonistic organisms, just to prevent against a specific disease. But if you were to take the whole package, mycorrhiza fungus, plus all the associated organisms, some of which, many of which might be antagonistic to pathogens, that would be a good approach, a good systemic approach. But it's an expense. And many growers are probably looking at that expense and saying, well, I don't know if that's going to be worth it or not. So they almost talk themselves out of trying it.

You know what I find interesting about the comment that you just made is this. Last week I was at an event in Iowa and corn growers. I've lost my desire To I enjoy working with corn less than I do with other crops. I'll just state that in a very kind way because of the agronomic approach that is so commonly taken. What I found so intriguing is that growers have become so locked into a system, they know that they're going to lose money when they plant corn seed in the ground. They know that's a foregone conclusion. And yet they, in the week that I was there, they were considering planning the following week to go out and put on a $40 an acre fundraisement application. That is completely unwarranted. There is no need for it. There are no pathogens present, there is no disease present and there is none in the forecast particularly. But the only reason they are putting it on is because they've been told they need it so that they don't lose any more money than they're already losing. And so I find that approach, that way of thinking about product applications, what if we were to think about our biological products that way? What if we were to think about mycorrhizal fungi and I can't afford not to put these on, otherwise I might lose more money than I'm already losing anyway. That was just kind of a twisted reality. Made me think that I might have gone through the looking glass, so to speak, and have been in a very different world. And then also, before we go on to other topics, I wanted to for all of our listeners, I'll be sharing the paper that Bob has referenced a couple of times. I've read it several times over the years and I'm really fascinated by the Ashburner example that is described in this paper because the way this defined and described is quite interesting. In the paper it's described as developing a mulch layer on the soil surface to foster the development of microbial communities and also to supply abundant calcium and then a very key phrase, to supply all the nitrogen in the form of ammonium. That to me means the presence of a reducing environment in the soil profile, not an oxidizing environment.

It's all part of the system.

It's all part of the system.

That aspect I'm not sure how Ashburner thought that through and developed the system. Actually, Ken Baker, who was one of the co authors on the paper.