When dealing with fungi, it is never just the organism itself that is the problem, but also the many mutualistic relationships it has in the soil. In some cases, those relationships are antagonistic and can be used against fungi that attack crops, such as by using specialized mycoviruses.

But even in the cases where the bacteria and viruses assist the fungi in its actions, that is still a key synergistic point that can be exploited to the benefit of farmers worldwide. And that’s just the case in today’s topic involving fungi and bacteria.

Researchers from the University of Florida have recently published a paper discussing a new finding involving Rhizoctonia genus fungi and specifically the pathogenic fungus Rhizoctonia solani.

The King Of Disease-Making

This fungi is a bit of a nightmare, along with being a surprisingly good jack of all trades. It’s not uncommon to find a group of related fungi species that prey on a wide variety of plants thousands of miles apart or even for a single species to prey on several different plants itself, but R. solani put all of its points into diversification.

By itself, R. solani is responsible for the turfgrass disease called brown patch, sheath blight within rice, root rot in sugar beets, and a host of other diseases found in soybeans, potatoes, and cucumbers, just to name a few. The list honestly goes on and on.

And how damaging these effects are vary depending on the disease, ranging from killing just 25% of an infected crop to a full-blown 100% crop die-off. Rice farmers especially abhor this fungus. This variety also makes it incredibly difficult to calculate just how much money in yield loss occurs annually from this crop pandemic-causing fungus.

Bacterial Friends

But let’s get back to the good news. The scientists in Florida, while studying the effects of R. solani on a patch of turfgrass, also looked into the bacteria that appeared to be involved in the soil whenever the fungus began growing. What they found was that bacterial species in the genus Enterobacter were living endosymbiotically within the hyphae of the fungi.

Interestingly, they were found in never before seen spherical cellular shapes within the hyphae’s channel, making it difficult at first to properly identify them as Enterobacter. But using anti-Enterobacter antibodies, they found that they bound to the spherical shapes, confirming what they were.

Some further experimentation whereby they eliminated the bacteria within a test subject fungi showed that, without its symbiotic bacteria, the fungi was not able to act at a 100% virulence level. Furthermore, it wasn’t able to produce the toxin phenylacetic acid at anywhere near the same levels.

Options For Control

These results explain a number of confusing traits of R. solani looked at in the past, where some would exhibit hyper-virulence and others would be practically nice when infecting a target plant. It is likely the involvement of these Enterobacter bacteria that made the difference and R. solani individuals lacking them are unable to act at full capacity.

With this discovery, several methods are opened up for future control of R. solani diseases. A direct option is to target the bacteria within the fungi and reduce its ability to be virulent by a significant amount.

Another possibility is to discover the specific genetics in how the bacteria is able to improve its symbiotic partner and potentially reverse this effect, reducing the virulence levels even more or maybe even outright killing the fungi from the effect.

Back To Work

All of this is, for now, just hypothetical. Much more research needs to be done after this discovery and likely many scientists are working on it as we speak (and as you read).

But if an effective method to control R. solani is developed, it will be a boon for a wide variety of crop farmers the world over.

Press Article Link

Study Link

Photo CCs: Rhizoctonia solani symptoms on bean roots from Wikimedia Commons