When a Biological’s Mechanism Seems to be Changing…

When the biological’s mechanisms change….

Have you seen a biostimulant have different effects depending on the crop, the timing of when you apply it, how you apply it, the rate at which you apply it, or all of the above? This seems to be a common element of biologicals, and an incredibly frustrating one at that. How is it possible that a product with consistent actives, consistent manufacturing, and consistent product composition can have different effects, even within the same crop species?

In my decade of agriculture research, I have seen this come up in many forms. Perhaps the biostimulant sometimes induces potatoes to have larger tubers, while at other times there are more tubers, but they’re smaller. Perhaps sometimes the biopesticide induces a growth stimulation response in addition to disease control, other times it seems to actually induce a yield drag, DESPITE its effective disease control. Sometimes a biofertilizer seems to effectively increase nitrogen uptake, other times it somehow reduces nitrogen uptake. HOW CAN THIS BE?

Several factors influence a biological’s consistent performance.

Of course, there are often inconsistencies in product manufacturing, depending on the sources of the product actives. Perhaps the harvest season varies the primary actives in seaweeds, or the protein source may affect the amino acid profile in protein hydrolysates. If the product is a live microbe, that microbe may have huge variability in what it is doing (and producing) during its own life cycle, which would of course affect a finished product’s final composition and consistent performance.

But let’s remove all the factors that influence the product’s consistency itself, and let’s say that we have a biological with consistent raw ingredient sourcing, consistent manufacturing process, and consistent product composition in the jug on the shelf. HOW can it be that this product will still produce inconsistent results in the field?

I will live and die on the soapbox that we far too often treat biological products like chemical products.

What do I mean by that?

It is very easy for us to see a list of actives in a biological product and think, “if we can isolate the ‘actives’, and concentrate them or produce them purely, then we will have a more effective and consistent product”.

But what is the problem with this mindset in biologicals research?

A few things.

First, we often assume that a combination of products will produce a predictable response.

We assume that if we have 3 actives, and each of these actives produce a known effect, then we can expect all three effects. But is this actually true? Sometimes 1 + 1 + 1 = 3, but in biology, sometimes 1 + 1 + 1 = 1. Sometimes 1 + 1 + 1 = 10. It really depends on what the actives are, and how the plant “perceives” these things. If a plant perceives a product as a foreign entity, that it needs to protect itself from, it doesn’t matter how nutritionally rich that product may be, the plant will try to defend itself against it and respond with a defense response. If an active is a conjugated hormone of some form, the plant may respond in excess, at the expense of its own regulatory system, which may negate other effects that the other actives may have, having been “outshined” by the conjugated hormone.

Second, we tend to think of plants as static machines, but my goodness, they are not.

Yes, it is true that we can assume a plant will have a predictable physiology, growth cycle, and nutritional requirements. However, plants are far from static. While it’s an overused trope, it is still true that “Plants are sessile and can’t run away from their threats, so they must adapt and respond to their environment.” We sometimes forget that crops are just plants that we use for food, fuel, or fiber. Yes, they have predictable physiology, but they will still respond to their environment in varying and dynamic ways. This is very often seen in their responses to biologicals.

Let’s say a biostimulant has microbial components that, while not pathogenic, the plant perceives as a possible threat. In response, it mounts a mild stress response with ethylene, Jasmonic acid, and salicylic acid signaling systemically, and let’s say this response lasts for about a week. Depending on the crop, and the stage of growth this crop is in, the physiological effects of this mild stress will be different. If we apply this just prior to fruit ripening in grapes, perhaps the ethylene and salicylic acid signaling will also increase expression of SAG’s (Senescence associated genes) that regulate the fruit ripening process, which could result in fruit ripening a week earlier than it would have without the product application. If we applied this same product, which elicits the same mild stress response, during early vegetative growth, we wouldn’t see this effect at all – the plant was nowhere near reproduction and the effects of this stress are perhaps long worn off by then. If we applied this mild stress to apples just prior to coloration, when the fruit is producing anthocyanins for pigment, perhaps this mild stress which elicits salicylic acid signaling, part of the shikimic acid cycle, may also push other downstream steps of this cycle, like condensed tannins, lignins, and…anthocyanin production… producing more pigment and thus a fruit with more red in its peel.

The possibilities of this application are truly endless, but you can see how despite consistent product composition, and perhaps even a consistent “response” in the plant (in our pretend case, a mild stress response), the effects in the plant can still be extremely varied.

Third, we often think of biological responses in a vacuum and forget their complex environment.

We  get this right when we understand that a live PGPR needs certain environmental conditions to establish itself and grow and give its benefits to our crops. However, so many factors influence not only how well a biological product works on a crop, but even the nature of what it actually does to the crop. If a crop is nutritionally stressed, even if it's not a yield-limiting stress, this may influence how the plant responds to a complex cocktail of biological actives. If there are disease pressures, even if they aren’t yield limiting, but the plant is already stressed, this will likely influence its response to the biological you apply to it. If a plant has a certain genotype, that renders it really resistant to certain diseases, but potentially vulnerable to heat stress, this will affect how the plant responds to an additional stress.

So what should we do?

It can be overwhelming to consider all the factors that influence a biological product’s inconsistent results in the field. I should also qualify that, yes, these same assumptions can happen when researching synthetics or traditional chemistries, but there is a different level of complexity and nuance when you have a single known molecule versus a complex cocktail of potentially hundreds of known (and unknown) molecules. I believe we will continue to uncover complexities for years to come. However, I also believe that if we can start to reframe a few of our assumptions to see biological products within their complex “biological” context, we can do better, more reliable research that gives us data to understand biological products better and achieve more consistent results.