Biologicals – Good Microbes Vs. Bad Microbes

When you first move to a new city, you may not know where to shop for food, or how to get from one place to another, or even the safe areas from the dangerous areas.  You are at a disadvantage to those who live and are already established in the city. 

When you place a biological fungicide (microbe) on a seed, and plant that seed in the soil, it’s much like a person moving to a new city; the introduced microbes are at a disadvantage.  Establishing a population of introduced microbes in the soil is difficult. The established microbes occupy the spaces where the food is, and are established, because they are especially adapted to grow and survive under those particular conditions. 

Microbial Soil Populations

There are many microbes in the soil.  Most neither help nor hurt plants.  A few are directly beneficial to plants by promoting plant growth or by making nutrients available to the plant.  There are also a few that can cause plant diseases.  Those that cause plant diseases, we’ll call the “bad microbes”.

And then… there are those microbes that do battle with the microbes that cause plant diseases.  These we will call the “good microbes”.

Many scientists have looked for, and found “good microbes” for possible use as biological fungicides.  When a scientist finds a “good microbe” in the soil and then applies the purified “good microbe” back on a seed, he/she is asking the microbe to establish itself in the soil and prevent the “bad microbes” from causing plant diseases.  This is a lot to ask. 

In order to establish introduced “good microbes” in the soil, and have them protect the plant, there must be something about your “good microbe” that gives it an advantage over the well established microbes in the soil, making the odds better for the “good microbes” to protect the plant against the “bad microbes” that cause plant diseases. 

Two Ways that “Good Microbes” can beat “Bad Microbes”

Antagonism

Researchers who develop biological seed treatments look for “good microbes” that are antagonistic against the “bad microbes”.  Some “good microbes” can release substances that prevent growth or kill the “bad microbes”.  The picture shows bacteria in the center of the plate with fungi growing all around it.  The bacteria are releasing a substance that prevents the fungi from growing any where near the “good microbe” in the center of the plate.  Establishment of this “good microbe” on plant roots could create a zone of disease protection for the plant.

Site Exclusion

Another strategy, is to find a “good microbe” that is exceptionally fast growing, and able to physically occupy most of the spaces where there’s food on the seed and plant root.  If you can occupy these nutrient rich spaces before a “bad microbe” can get to them, you can prevent infection by the “bad microbe”, and limit plant diseases.

Biological Fungicides on the Market

There are many “good microbe” biological fungicides available on the market as seed treatments.  In general, chemical fungicides still seem to be the most consistently effective seed treatments.  It has been suggested that combining chemical seed treatments with biological seed treatments may extend the length of plant protection over chemicals alone.  It has also been thought, that a chemical seed treatment that deters the growth of soil microbes without hurting the “good microbes” may give the “good microbe” enough of an advantage to establish itself on the plant.  Both of these thoughts suggest a possible synergistic relationship between certain chemicals and biological fungicides in the future.  Time will tell.