Soil microbes can help plants resist disease

Soil transplants similar to medicinal fecal transplants can transfer improved resistance to the next plant generation

A study by scientists at the University of York in the United Kingdom has shown that improved disease resistance can be transferred to the next generation of plants via soil transplants.

Dr. Ville Friman at the university’s Department of Biology said the positive effects of so-called suppressive soils has long been known.

“However, it has been difficult to show what type of bacterial communities might drive these effects causally.”

He said research carried out in China found that bacterial wilt infections are patchy, and even though researchers found the pathogen everywhere they took samples, not all the plants (in this case tomatoes) became infected.

“This pointed us to focus on all the other bacteria and their significance for this phenomenon.”

He said the beneficial effects of the microbes can be retained in the soil for some time and over several plant generations, which shows that suppressive soils can be fairly stable after only one application.

“Maybe, in the future, it will be possible to rectify soil imbalances using targeted and specific inoculations from suppressive to conducive soils.”

Bacterial wilt is caused by Ralstonia solanacearum. It infects tomatoes and potatoes and causes major economic losses around the world, especially in China, Indonesia and Africa.

However, growers and scientists have been at a loss to explain why the pathogen can be present in a field of tomatoes, and yet not all the crop will be affected. Infections can be patchy.

The study aimed to find the factors that allowed the spread of disease in some parts of the field, but not in others.

To study the effect this, Friman and his team used a newly developed experimental system.

“In principle, it is a series of pots with permeable walls (iron mesh) that leave space in between the pots for individual nylon bags that can be filled with soil and removed throughout tomato plant growth and development without damaging the root system too much,” said Friman. “The microbes in the bag will have been affected by plant root exudates and hence represent the rhizosphere bacterial community.”

They were able to compare the micro-organisms present in the soil of both the healthy plants and those that became infected.

The analyses indicated that the microbiomes surrounding healthy plants were associated with certain rare taxa and pathogen-suppressing Pseudomonas and Bacillus bacteria.

He added that soil bacteria can produce many different compounds with a broad range of antimicrobial activity against different bacteria. Bacillus species have been shown to inhibit pathogenic fungi such as fusarium, for example.

“New sequencing techniques are definitely improving our understanding of microbe-plant interactions and more people are into conducting direct experiments where we can try to observe which factors are driving the outcomes of these interactions from the plant perspective,” said Friman. “For example, Rhizobia and mycorrhiza have been acknowledged to be important for nitrogen and phosphate availability and we are now starting to unravel the importance of other important bacteria for plant growth and disease suppression. I think we are truly living in exciting times.”

Ongoing research includes exploring what other microbes, such as fungi, protists and bacteriophages, do for the soils and how they are linked with disease outcomes.

The research paper, Initial soil microbiome composition and functioning predetermine future plant health, was recently published in Science Advances.

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