if the pathogens can’t bring about that compromising of the availability of manganese by converting it to an oxidized form, the fungus is essentially just a good saprophyte in the soil.
Don Huber describes for us once again that ‘disease’ organisms can only produce an infection in the correct environment. In a healthy environment, these same organisms develop symbiotic relationships with the plant. Our task as farm managers is to manage the environment properly, and crop ‘dis-ease’ vanishes.
You can listen to the entire episode here.
Don: A lot of your nutrient relationships—where you have microorganisms that are responsible for changing the valence states of various minerals so that they’re more available or less available. And you have those going on in both directions at the same time in some capacities. It’s an issue with manganese or iron or some of those things. Some of the secondary functions come into play so that all of that can take place and manifest in a very positive manner. Even though what you might be looking at—or the tests that you have—may not show the complete picture, you have to realize that it has to be going on, in order to complete the cycle.
And so, it’s a matter of either developing the techniques or understanding how all of those organisms interact—the ecological niches that make the system work. Everything isn’t just one big pool with somebody stirring the whole thing around. You really have a community of functions that are taking place at the same time, but you don’t have the same gas station at every corner or a grocery store at every corner. You have each one of those different functions taking place in its own little scheme of things. So the overall system is a very functional and very dynamic relationship relative to the plan. And it’s neat.
John: One of the pieces that you and I have discussed in the past is the challenge that we are seeing today with manganese availability. I would say that as much as 80 percent or more—perhaps even 90 percent or more of the crops that we work with today—come back showing inadequate levels of manganese. What are the major factors that contribute to that?
Don: Manganese has a very dynamic relationship with the soil, and also with many of the fungi. There are organisms—mycorrhizae—that increase the uptake of manganese, as well as zinc and phosphorus and some of the other nutrients. So, if they’re not functional, you miss that ability to absorb and to interact with a tremendous volume of the soil—where that mineral might be in short supply.
The other thing is that you have bacteria that are responsible for the valence state. You have the oxidizing groups. You have the reducing groups. The plant can utilize only the reduced form of manganese—the Mn2+ form. Mn4+ form is non-available, but we see it primarily in the soils that have high phosphate levels or high oxidative relationships—the manganese can be there and yet not be available for uptake. We see it with many of our pathogens, because the pathogens utilize manganese oxidation as a virulence factor.
We looked at several thousand isolates of Gaeumannomyces graminis, which causes take-all all over the world. We evaluated those and we found that there was one characteristic that was common in all virulent farms—manganese oxidation. If the wheat had oxidized manganese, it would never resist the disease. The same thing for rice blast. The same thing for isolates of Streptomyces scabies and a number of other pathogens. The ability to oxidize manganese to a non-available form—and to compromise the resistance of the plant to those pathogens—if the pathogens can’t bring about that compromising of the availability of manganese by converting it to an oxidized form, the fungus is essentially just a good saprophyte in the soil.
Same thing with many bacteria. So, we see these direct effects on mineral availability being involved not just in growth and quality and nutrient density, but also in susceptibility or resistance to disease. You have the virulence relationship of the pathogens with bacteria and fungi in the soil, and that’s related to those minerals that are necessary for the plant’s defenses. Those minerals are also directly related to the growth and resistance of the plants to those pathogens in their overall physiological function. It all fits together very nicely if the system is balanced—if it’s favorable.
And that’s one of the things that we can adapt to. When we’re farming, we’re really managing an ecology. It’s not a matter of a silver bullet for this problem or a stinger missile for another. It’s really a matter of having ecology work for us and support the plant. And if we don’t do that and we upset the system, then we compromise the overall quality and productivity potential we have in our soil.
John: You said that there are a number of pathogens that are dependent on manganese oxidation. And if they’re unable to oxidize manganese, they just become saprophytes in the soil profile. Are they dependent on that manganese oxidation directly—do they individually require it? Or are they just producing a manganese-deficient plant that is now susceptible to invasion?
Don: Both of those statements would be correct. They don’t necessarily need the oxidation. Some of them are also reducing organisms. In other words, if you change the environment—or if you change the association that they have with other organisms—then they may be strong reducing versus strong oxidizing organisms.
We see that especially with the Pseudomonads and a number of other organisms—you change the soil environment and they can benefit you, or they can be synergistic, or they can even be a direct pathogen, involved in compromising that resistance. The microorganisms use those minerals just like a plant does, or just like we do. Our metallo-nutrients, or strong transition elements, or electron transfer and physiological processes, are the cofactors for enzyme function. We don’t require very much of them, but if you don’t have that specific cofactor that’s involved for an enzyme, that enzyme isn’t going to do any work for you—it’s just another protein that’s sitting there. And about 80 percent of our proteins in plants are what we call metallo-proteins, where the metallo part is a cofactor. It’s a small part, but a very critical one, as far as function of that physiological pathway.
John: In essence, what you’re describing is that as long as plants have adequate availability of reduced manganese, they have resistance to all the diseases that you described.
Don: It would be very, very critical for that resistance—for the physiological functions in in the plant—without those minerals.
If you have read this far, you are welcome to join us for a webinar June 19th, at 11 AM EDT where we will discuss how to increase reduced manganese availability in soils.