As any plant lover knows, fungal infections can be a harbinger of doom for vegetation.
One day your cherry tomatoes are going gangbusters in the garden and, seemingly overnight, sunken brown spots appear on the plant's leaves, withering the foliage and the fruit ripening on its vines. Thanks, tomato blight fungus.
In blade grasses, such as turfgrass found on golf courses, athletic fields and lawns, dollar spot disease presents a similar challenge. The fungal disease is characterized by the appearance of circular spots of dead turf about the size of a silver dollar, hence the name dollar spot. It is a costly problem that can run upwards of $35,000 per year to manage at an average U.S. golf course. Multiplied across an approximately $40 billion turfgrass industry, mitigation measures are much needed. Therapeutic treatments made from biological materials, such as bacteria or microbes, are a promising solution for such situations.
Take UD1022 — a unique, University of Delaware-developed beneficial bacterium proven to boost plant defenses. Discovered by UD plant biologist Harsh Bais and colleagues, this novel strain of Bacillus subtilis helps a variety of plants resist soil‑borne diseases, retain moisture and develop stronger root‑to‑shoot growth, among other benefits.
In previous work , Bais and colleagues showed in lab studies that UD1022 was effective in controlling the growth of dollar spot fungus, Clarireedia jacksonii, found on turfgrass.
Now, further research reported in the journal Plant Stress on the effect of UD1022 on dollar spot suggests intriguing implications for manufacturing of biological treatments for the fungal disease.
In the paper, the research team showed that when they tested whether soil treated with UD1022 would be enough to prime turfgrass plants' innate defense response to resist dollar spot infection — the way a flu vaccine primes the body to resist the flu virus — it wasn't.
This was curious, as the Bais lab previously had shown UD1022 effective in priming other plants, such as tomato, Arabidopsis and rice, against various fungal and bacterial pathogens.
"It turns out that UD1022 is good at biologically controlling the growth of dollar spot in turfgrass, but only when the bacteria (UD1022) and the fungus (dollar spot) are in front of each other," Bais said.
Indeed, when the research team applied UD1022 directly to leaves affected with dollar spot, the plant experienced a 43.6% reduction in disease severity. But when the researchers applied UD1022 in the soil at the root level and later introduced dollar spot fungus on the leaves, there wasn't a huge decline in disease symptoms on the leaves. This confirmed that while applying UD1022 to the root does trigger an innate defense response in the plant, it's just not enough to ward off infection in the leaves, far from the root system.
"It's like there's a break in the communication line, and the mechanism of how UD1022 acts against dollar spot is very different," Bais said. "With dollar spot fungus, UD1022 has to be there directly to antagonize the fungus."
This coincides with the research team's findings that results waned over time, which would inform formulation and application approaches for treating the disease. And if UD1022 is present on the leaves, but not alive, no go — the dollar spot fungus grew — which showed the UD1022 must remain viable to continually antagonize the fungus.
Taken together, Bais said these findings are informing what is known about biological approaches for mitigating dollar spot disease in turfgrass. For example, while UD1022 cannot do the whole job of deterring dollar spot in turfgrass, it can offer a more sustainable disease management strategy when used as a complement to currently available approaches already in the market. In addition, it is known that UD1022 can also increase drought tolerance in turfgrass, so it is a microbe that has both positive and negative effects on living and environmental stressors a plant might encounter that would benefit from the continual presence of UD1022.
"Biologicals like UD1022 cannot solve everything — it's not a silver bullet. You need to keep evolving your approach," Bais said.
Bais hopes to develop a new pipeline for biologicals like UD1022, with the potential to make greater headway against plant pathogens. Along those lines, he plans to explore the compatibility of a synthetic microbial community composed of 10-15 beneficial microbes that his laboratory has isolated over the last 21 years for use in multiple systems, during sabbatical work at Pacific Northwest National Laboratory (PNNL) in 2027.
According to Bais, the biggest challenge in using a microbial consortium is evaluating the level of persistence of these microbes on the root surface. Bais said this is because root colonization by benign microbes is the most important factor in triggering plant health benefits against living and environmental stressors.
"Using a champion root colonizer like UD1022 in consortium with other beneficial microbes, it will be interesting to evaluate the community for root colonization and its subsequent implications on plant and soil health," he said.
The future work will involve using this synthetic microbial consortium in a turfgrass system or other staple monocots (single-bladed plants) like sorghum and corn, to test UD1022's effect and plant response under realistic environmental scenarios, such as drought and dollar spot together.
"Plants go through multiple stress at a time, they don't grow in isolation, and the compatibility of microbes in a community is very important," said Bais. "For example, usually when plants go through a physical stress such as drought, they're more prone to fungal infection. It's something we're interested in at this point in time, and this paper provides a segue to our next work."
Co-authors on the paper include Bais, Charanpreet Kaur, the paper's lead author and a research associate in the Bais lab, and Erik Ervin, professor of turfgrass and horticultural systems and associate dean in UD's College of Agriculture and Natural Resources.
