Good Microbes vs. Bad: Antibiotics for the Soil

Tuesday, December 12, 2017

In my last newsletter, I talked about how the introduction (inoculation) of new microbes can benefit poor soils and struggling crops. On the other side of the coin, devastating fungi, bacteria and other microbial parasites can contribute to a host of crop diseases. In the 1960s, millions of elm trees in Britain, France and the US fell victim to Dutch elm disease, which clogs the vessels that carry life-giving water to the trees’ leaves. Starting in the late 1980s, Brazil’s thriving chocolate industry crumbled when witches’ broom disease devastated its cacao trees. Lately, banana growers have become increasingly concerned about Panama disease, which is spreading rapidly and threatening to wipe out their crops.

Desperate to find a way to fight back, scientists have turned their attention to a special type of soil known as “disease-suppressive soil.” This is significant, and it’s where the new world of agriculture science is heading as we’re discovering that the right combination of microbes can fight off disease. As when our bodies gain defenses in the form of antibodies after we get sick with chicken pox or measles, soils can develop defenses using a combination of microbes that fend off future attacks from the same pathogen.

In the 1990s, Linda Kinkel and Neil Anderson, plant pathologists at the University of Minnesota, went looking for a microbial explanation for an inexplicable decline in scab, a disease that disfigures crops like potatoes or radishes with dark, splotchy growths, in a potato field in Minnesota. Kinkel and her colleagues found that the soil of the resistant crop contained greater amounts of a bacteria called Streptomyces than the soil that did not suppress disease. The  Streptomyces bacteria produce antibiotics as weapons against parasites.

“Technology provides a static picture,” says Kinkel, “but these systems are so not static. … We need to understand not just which species are present, but how they are interacting.” I couldn’t agree more: the microbes are interacting and colonizing to fill gaps in the soil microbiology. In addition, we know that microbial diversity is directly connected to improving plant immunity. There is no magical microbe that can be added to soil to fight off disease, as it’s a complex system working in harmony, like all natural ecosystems.

Society is pressuring farmers to use less harmful applications like pesticides and fungicides. Understanding the strengths and capabilities of these microbial fortified soils and their ability to suppress diseases without any pesticide input could be a game changer.