How soil microbes are losing the battle against crop diseases
Just as there are helpful microbes inside our bodies, there are countless microbes in the soil around plant roots. But what happens when antibiotics disrupt this balance?
Antibiotic use can weaken support from helpful bacteria in the soil, making plants more susceptible to above-ground disease, a new study has found. Much like an altered gut microbiome affects human health, tomatoes can disrupt the growth of microbes in the soil around plant roots and leave them vulnerable to disease.
In agriculture, antibiotics are often used to combat crop diseases. Increasing antibiotic resistance and the impact on pollinators and beneficial microbes has led to stricter regulations on antibiotic use in agriculture across Europe. As antibiotic use in agriculture continues elsewhere, understanding its impact on plant health and encouraging more sustainable agricultural practices is critical.
The soil around the roots, called the rhizosphere, is rich in countless microbes, similar to the human microbiome. The roots secrete various substances, which attract beneficial bacteria. And in turn, release molecules that help the plant grow while fending off harmful disease-causing microbes. And just as an altered gut microbiome can make humans more susceptible to disease, an imbalanced rhizosphere can also affect plant health. Dysbiosis, as it's known, has been shown to damage tomato plants for underground health.
Samuel Martins says,
"Many previous studies have shown how rhizosphere dysbiosis is linked to below-ground diseases," a researcher at the University of Florida, Gainesville, USA, said in an e-mail. An imbalance in the rhizosphere can make the plant more susceptible to foliar diseases." To test their theory, the team worked with tomato plants, which are commercially important and grow quickly. They investigated the effects of a common antibiotic, streptomycin, on tomato plants infected with the bacterial leaf spot pathogen (Xanthomonas perforans), an important threat to tomatoes.
The team administered streptomycin to weaken the rhizosphere of a three-week-old tomato plant. And for control, a bunch of tomato plants were given only water instead of antibiotics. Streptomycin is used in greenhouse tomato production in America and Asia while banned in Europe. But the increased use of antibiotics creates problems with the spread of resistance among bacterial pathogens.
Martins said,
"Since the 1950s, antibiotics have been used in agriculture to treat bacterial diseases of plants, both under controlled conditions (eg, greenhouses) and as field sprays. Surprisingly, these antibiotics are the same ones we use to treat human diseases.
But now the question is: What is the effect of antibiotic application on plant microbiome and plant defense?
About 24 hours after using the antibiotic, the researchers sprayed the harmful bacteria on the leaves of all the plants. And similar to the use of faecal transplants in humans, soil microbiome transplants from healthy plants have been applied to those with dysbiosis with some success. That is, the team did this transplant for half the plants 48 hours after streptomycin application.
Tomato plants experiencing antibiotic-induced dysbiosis showed more disease symptoms at days 13 and 15 than control plants. Plants with transplants fell somewhere in between—they experienced fewer disease symptoms but not as much as control plants. However, these improvements were not statistically significant. According to Martins, it may take longer to reset the dysbiosis.
The research team also observed changes in gene expression, and found that there are several genes involved in increasing plant defense and immunity.
Plants affected by dysbiosis showed a sharp decrease in the diversity and abundance of their microbiota, which included Cyanobacteria, Actinobacteria and Pseudomonas. Plants that replaced soil showed very little improvement in microbial diversity and abundance. The research team also observed changes in gene expression - several genes involved in plant defense and immunity enhancement.
"It is expected that a xenobiotic can modify/damage the microbiome, but its effect on plant health is a novel direction for the root to shoot messages for foliar diseases in particular," says Bice.
The team is interested in identifying the root cause. But the absence of these germs increases the severity of the disease. Adding these microbes back into the soil can help protect against disease without the full use of antibiotics. Martins added, "The findings emphasize the need for strategies that preserve or restore beneficial microbial communities to enhance plant resilience against pathogens.
Source :- https://enviromicro-journals.onlinelibrary.wiley.com/doi/10.1111/1462-2920.16676
Mehedi Hasan Shihab / Own Correspondent
