About a month ago, Neha and I discovered our tomato plants were wilting in a mysterious manner. Almost overnight, entire plants were withering away into sad, deflated versions of themselves. Still green, just unable to manage turgidity. A bit of research later, we found that we had an infestation of bacterial wilt. (We confirmed this via an easy, 2-minute test, needing nothing more than a glass of water, it’s featured below…)
What Is Bacterial Wilt?
An infection caused by the bacterium Ralstonia (Pseudomonas) Solanacearum. As the name indicates, other members of the family Solanaceae, such as potato, eggplant and tobacco are equally susceptible. Sure enough, some brinjals were also starting to suffer the same fate as our tomatoes.
There was good news, though. Thanks to our emphasis on increasing bio-diversity, we were growing far more than just Solanacae. Our greens, chillies, beans, gourds and squash were doing just fine, and starting to provide harvests.
How Does Bacterial Wilt Do Its Thing?
Bacterial wilt enters the plant through cuts in the root, which happen during planting, or naturally via nematodes or insects. The bacteria then multiply in the vascular system, eventually clogging up the water conducting vessels with bacterial cells.
How To Confirm Bacterial Wilt
The easiest way to confirm your garden has a case of bacterial wilt is to cut a stem section from a suspected plant, and then immerse it in water for a few minutes. If wilt is an issue, the bacterial slime will begin to flow from the xylem into the water and you’ll see it as a cloudy, murky stream issuing from the cut end of the stem.
What Can You Do About Bacterial Wilt?
Sadly, there are no known ways of eliminating bacterial wilt other than solarizing the soil, a process whereby the sun’s heat and UV light is used to sterilize the soil (down to a depth of at least two feet). Then you rebuild all life, from scratch. A drastic and painstaking effort, and at the end of all of that work, you have to be incredibly paranoid about reinfections as well. Clearly this is a last-ditch cure. For us, the worst case scenario would have been to grow Solanacae in containers with solarized soil. Not great, but not devastating.
A Potential Solution?
While we waited to decide what to do about the tomato plants, we began casting about for any other solutions. Among various research papers I read while investigating bacterial wilt, I found “Low sodium chloride priming increases seedling vigor and stress tolerance to Ralstonia solanacearum in tomato”, a 2011 paper written by a group of Japanese researchers investigating the use of a salty solution (of NaCl and water) to prime, or soak the seeds in before planting. Apparently this is a method used to synchronize seed germination, but it also was suspected to improve the plant’s resistance to bacterial wilt.
Their research showed promise. Not only was the treatment easy to administer (just soak the seeds for 24h in a specific concentration of salt and water before planting) but the results appeared incredible:
In this experiment, which was run twice (A & B) with 13 plants each time, the NaCl-primed plants wilted at a rate between 40% and 60% less than plants primed with water or not primed at all.
OK, we are trying this. 40% to 60% means if we double the number of plants we put in, we’re back to normal!
The Salt Solution
The first step was to make the 300mM salt solution that the seeds had to be soaked for 24h. A bit of figuring out concentrations and molar masses later, I had the recipe. I needed to put in 19.48gms of salt into a litre of water. (Actually it gives me a 333mM solution, but since I’m doing a real-world test of this method, it needs to also tolerate imprecision like this.)
Once the salt solution was ready, we dropped the seeds in, set an alarm and waited for 24 hours.
We planted four varieties of tomato, to test each one. Sungold Select II cherry tomatoes and Black Krim tomatoes from friends’ farms, Yarroway Farms’ Roma Tomato and a variety of beefsteak tomato called Delicious, from a previous season at The Habitat Homestead.
After 24 hours, we fished out the seeds, washed them in running water and planted them.
Tucked in and waiting for germination!
At this point, our fingers are crossed, hoping for a good germination rate, followed by robust growth and a resistance to the wilt. Will it work? We’ll know in a few weeks! Look out for part two of this post at that time!