Transporting Nutrients throughout the Plant — via Bacteria

Q. What’s the role of silicon in plant disease management? 

A. In places where we have water quality issues, particularly in the southwest, we often have excess of levels of chloride, sodium, bicarbonates, etc. It’s been known for a long time is that silicon gives us resilience to stress and resilience to these electrolytes. Silicon contributes significant plant health benefits — when applied in the right amount. But when you apply too much, it actually goes the other way or is neutral. 

There were lots of experiments to identify the optimal application rates of silicon, only to discover that the optimal rate is variable. It depends on the field conditions and the crop, and if we apply too much, we lose the potential positives. 

However, most of the experiments with silicon application used a purified chemical form of silicon that the plant has limited ability to regulate. When the plant absorbs silicon from the soil, through the rhizophagy cycle, all of that goes away. Through rhizophagy, the plant can regulate where it wants to position the silicon and how it wants to move it, and all of a sudden silicon is very effective for disease control.

There’s been a belief that calcium and silicon and boron are not phloem mobile — that they’re only xylem mobile — that they need to be transported with the water straight from the root system up to the plant. But we now know that there is phloem mobility of calcium and silicon and boron — when they are contained inside bacterial cells. 

Not only is there phloem transport when these nutrients are inside bacterial cells — there is even cell-to-cell transport. When plants are colonized by endophytes and the rhizophagy cycle is working, all of a sudden there is a mechanism to deliver calcium and silicon and boron from the soil to the upper parts of the plants in the absence of free water flow — as long as the plant is colonized by endophytes. It’s all about biology.