You stride through lush grasslands. The scenery seems perfect. But lurking just below your feet is a battlefield.
It’s not an obvious one, of course. There are no bombs going off or explosions or yelling; but there are millions of tiny creatures locked in battle for resources and life. And whoever wins determines whether the plant life above it survives.
This blog post has been inspired by research published in 2015 by scientists of Lincoln University, AgResearch, and their international colleagues. They examined whether soils from different pastures in New Zealand naturally inhibit soil-borne plant pathogens.
The Invisible Threat
Many important plant diseases originate underground rather than from the aerial parts of plants, such as leaves. They attack plant roots and stems before visible symptoms appear above ground. By the time one notices any symptoms of disease, the damage may already have been done.
And here is the scary part: these silent killers can reduce pasture productivity by 40–50%. Can you imagine how devastating it is to lose nearly half of your production to something unseen? Such is the case in pastures where crop rotation and chemical controls cannot always solve the problem.
Instead of asking the conventional question, scientists started to wonder:
What if the soil could defend itself?
Soil Is Not Just Dirt
It is easy to think of the soil as lifeless material, but this is far from the truth. Soil is one of the most biologically diverse ecosystems on Earth. A complete microbiota lives within it: bacteria, fungi, and other microorganisms interact continuously. While some assist plants in absorbing nutrients, others … kill them.
Some soils inhibit diseases. Such soils are referred to as disease-suppressive soils, and their action falls into two categories:
General suppression: the microbiota competes with the pathogen,
Specific suppression: some microbiota attack the pathogen itself.
Soils with high plant diversity likely contain more diverse microbiotas, which suggests a high disease-suppression capacity.
But how can one measure such a phenomenon?
A Clever Way to Test Soil
The researchers developed an interesting experiment to test the soil under examination. Rather than using conventional grass or legumes that can be found on pastures, they opted for something completely out of the ordinary: kale.
And why kale? This plant is not usually used on pastures. If disease does not occur, then it shows that the soil is pathogen-resistant in general.
Furthermore, they exposed the plants to a well-known pathogenic fungus named Rhizoctonia solani. And this one leads to a specific disease called damping-off. Plants affected by the disease exhibit dark lesions near the base of the stem which cause plants to fall, like broken wires.
So, basically, the process works as follows:
Introduce the same plant into different soils;
Infect the plant with the same pathogen;
Observe the results.
All Soils Are Not Equal
The experiment was conducted using four New Zealand pasture soils, including Lincoln, Eyrewell, Rotorua, and Kurow soils.
Same plant. Same pathogen. Entirely different results.
Some soils promoted rapid spread of pathogens; others reduced their effect considerably. There were significant differences between disease levels in the various soils.
- Final disease levels were highest in Rotorua soil.
- Disease progression rate was highest in Kurow soil.
- Lincoln soil displayed maximum resistance, with minimal disease levels in the control.
Same experiment. Different soil. Entirely different results.
And here comes the moment when it all becomes evident:
Soil is not just a neutral element. It actively influences the experiment.
If a soil keeps plants healthy, it’s suppressive. If plants collapse… not so much.
The Twist: Some Soils Had Been Infected Already
Without even having introduced the pathogen, some soils exhibited symptoms of infection. For instance, in Kurow soils, damping-off disease symptoms appeared in the control group as well. This indicated that the pathogen was already present but dormant until the required environmental conditions prevailed.
It could be termed an underlying threat embedded in the soil. Furthermore, pathogens, such as Rhizoctonia solani, can survive between successive cropping seasons, affecting both pastures and future agricultural crop growth.
It’s Not Only “How Many” but Also “How Quickly”
Besides assessing how many of the plants became diseased, the authors also took into account the dynamics of disease development. Why does this matter?
This is important because a slowly developing disease will allow the plants to develop properly before being affected. The faster moving disease will kill them much earlier.
Two metrics were used to assess this:
Disease Incidence (DI) – number of infected plants at the end;
Area Under Disease Progress Curve (AUDPC) – a measure of disease development over time.
Imagine that:
DI is the final result
AUDPC is the whole game
And often, their narratives may be very different.
Why It All Matters
It isn’t just scientific research for research’s sake. With knowledge of how soils resist disease, we could:
- Improve our soil management techniques,
- Cut down on chemical use,
- Increase productivity from our crops and pastures,
- Create a more sustainable agricultural process.
Rather than battling pathogens directly, we could fortify our soil against disease.
That’s where it gets revolutionary.
The Bigger Picture
Agriculture of the future may rely less on adding things to soil…
And more on what is already thriving beneath its surface.
When you look at a flourishing farm, remember this:
It is not only the plants that prosper. There is an entire ecosystem underground, sustaining all life. And in this unseen world, each microbe counts in the battle beneath our feet.
This blog was prepared by Vikram Shankar Malagi, a Master of Bioprotection student at Lincoln University, as part of an assignment for ECOL608 Research Methods in Ecology.
References:
Dignam, B. E. A., O’Callaghan, M., Condron, L. M., Raaijmakers, J. M., Kowalchuk, G. A., & Wakelin, S. A. (2015). A bioassay to compare the disease suppressive capacity of pasture soils. New Zealand Plant Protection, 68, 151–159.
http://www.nzpps.org/nzpp_abstract.php?paper=681510
.jpg){kind=link}
