Dr. Betsy Pierson, professor in the department of horticulture sciences for Texas A&M University, spoke at the Texas Plant Protection Association conference, stressing the importance of microbiome research for Texas growers.

Microbiomes are tiny ecosystems surrounding plants, involving microorganisms that contribute to a plant’s health and productivity.

Pierson, the 2017 TPPA academic/agency award winner and former president of TPPA, addressed research perspectives and the future direction of the biological product markets.

Quality & Quantity

Due to population increase, “not only will we need to up the quantity but also the nutrient and health quality of the things we produce,” Pierson said.

One approach for achieving these gains is via what has been dubbed as the Brown Revolution, which includes innovations for improved soil and root microbiome health that will increase plant productivity.

“Plants have microorganisms living on and inside them, and these microbes are capable of influencing plant development and physiology and protecting and nourishing plants,” she said. “This is what we are talking about when we say, ‘using the plant microbiome to unlock yield potential.’”

Hidden world

Pierson provided an in-depth look at the hidden world of plants, the roots and the soil, and the root rhizosphere microbiome.

“The soil is the largest reservoir of nutrients and microorganisms to which land plants are going to be exposed,” Pierson said. “Roots, like the human gut, are the primary organ for nutrient and water acquisition, and 95 percent of that acquisition takes place at the root tips. The root system architecture and physiology, in turn, allows the plant to adapt to stressful conditions.”

Plants recruit a microbiome comprised of soil-borne microorganisms that are capable of altering root system architecture, physiology and function in ways that are vital for plant development and stress response.

Root systems are huge drivers of the soil’s physical, chemical and biological properties and actively recruit a rhizosphere microbiome from the soil. Sixty percent of fixed carbon may be transferred to the root and up to 70 percent of that may be lost as rhizodeposition.

“This is not because plant root systems are leaky,” she said. “Rhizodeposition serves as a nutrient source for rhizosphere-colonizing organisms. This investment suggests these microorganisms are valuable to the plant.”

Microbial services

Pierson said there are many different microbial services that may be provided by rhizosphere-colonizing bacteria, including as biofertilizers, phyto-stimulators affecting plant hormones to help modulate stress and as biological controls against pathogens and insects.

Similar to approaches used to promote human health via the gut microbiome, “to utilize this potential, we can think about introducing or enriching these microbes as probiotics e.g., microorganisms that are essential for basic health,” she said. “We also can think about a complementary prebiotics approach, in which nutrients that are essential for sustaining microbial communities are introduced.”

Pierson said from a research perspective, a good approach for locating plant-beneficial microorganisms is using direct selection for the plant phenotype in a process called host-mediated microbiome engineering.

For example, plants can recruit microorganisms that help them be successful under water stress conditions. In a related project, Michael Jochum, a graduate student in plant pathology and microbiology at Texas A&M, has been studying how rhizosphere microbial communities change over multiple cycles of selection for plant water stress tolerance.

“Plants are indeed able to recruit bacteria that are able to help them with stress, and these bacteria may produce profound changes in root system architecture,” Pierson said. “For example, we have found that under water stress conditions plant root systems colonized by bacteria capable of producing bacterial metabolites, known as phenazines, produce larger root systems with more root tips, thereby extensively increasing their capacity to take up water and avoid drought stress.

“If you sample plant roots grown under dryland production, whether in Washington as observed by another research group, or Texas, nearly all the plants have roots that are colonized by bacteria capable of producing phenazines.”

Pierson also noted the registration process for biological products is shorter and less costly than for conventional synthetic chemicals, and biologicals are viewed as inherently less toxic than synthetic pesticides due to their smaller application quantities and faster decomposition.

Rotations

Additionally, she said to please both the customer and the industry, producers are looking to biologicals to be incorporated into rotations with synthetic chemicals in integrated pest management strategies. These rotations would serve to reduce the amount of synthetic pesticides being applied while extending the lifespan of existing chemistries.

There is huge growth not just in biopesticide markets, but in the plant biostimulant sector, looking at microbiome-type products that provide plant and soil enhancements, Pierson said.

“When we talk about biological products, this includes biopesticides, e.g. biological products that kill insects, pathogens and weeds,” she said. “Biopesticides include biochemical biopesticides, a category comprised of botanicals, minerals and other substances as well as microbial biopesticides, which are formulated from living microorganisms or their byproducts.”

She said these are typically derived from living bacteria, fungi, nematodes, resting spores or cysts of these organisms or biocidal byproducts of these. Currently, there are about 1,400 biopesticides regulated by the U.S. Environmental Protection Agency.

“Plant biostimulants are an emerging market and are comprised of substances or microorganisms that function to stimulate natural plant processes to enhance the availability or plant uptake of nutrients, improve soil quality, or mediate tolerance of abiotic stress such as drought,” said Pierson.

“It’s really an exciting time in the ongoing development of biologicals,” she said. “New approaches focused on the plant microbiome and recent advances in ‘omics’ technologies are providing a better, system-based understanding of which microorganisms and microbial functions are useful to plants. On the plant-production side, these advances may lead to plant breeding approaches to capitalize on microbial services as well as land management systems that enhance or sustain plant microbiomes.”