Understanding, preventing transport of plant pathogens in water

Researchers Mary Hausbeck and Wei Zhang are developing water-recycling technologies that filter out pathogens in greenhouse systems.

A soil physicist at Michigan State University (MSU), Wei Zhang, is drawn to some of the most challenging problems facing modern-day agriculture. He heads the Soil and Water Research Lab at MSU, a group of scientists tasked with identifying ways to utilize soil and water resources more efficiently.

How do we grow a greater quantity of healthy food for a rising world population? How can we address antibiotic resistance? How can we act as better stewards of the environment and reduce contamination? Zhang and his team aspire to answer these questions and to tap into the vast plant science expertise at MSU outside of his lab.

In March 2012 — just a couple of months after Zhang started at MSU — he attended a presentation given by Mary Hausbeck, a renowned plant pathologist and University Distinguished Professor in the MSU Department of Plant, Soil and Microbial Sciences. She has served the Michigan vegetable and greenhouse ornamental industries for nearly three decades, tending to crop disease issues as a researcher and MSU Extension specialist.

Hausbeck spoke to her colleagues about Phytophthora and Pythium, water molds that wreak havoc on a wide range of crops. Spores from these molds — called zoospores — can travel through water and infect neighboring plants, a chain reaction that can quickly devastate a grower’s operation.

Zhang primarily deals with the transport of contaminants within soil and water, so he believed this presented a collaboration opportunity to delve into plant diseases. Hausbeck agreed.

“I sent Mary an email, and she responded right away,” Zhang said. “Understanding and developing a system that allows for the filtration of pathogens from water is important, especially in greenhouses, where we ideally recycle water. This idea got us excited about the prospect of combining our work.”

Embedded within Zhang’s research program is One Health, a philosophy endorsed by organizations around the world that promotes the notion of human, animal and environmental health as interdependent.

“Every input into the environment has a consequence,” Zhang said. “It is important that we understand the effects of any of the tools we use to eradicate diseases and pests. The best outcome is one where we solve any problems while also keeping a low stress level on the plants, thus maintaining a lower stress level on the environment.”

With the One Health approach in mind, Zhang, Hausbeck and graduate students began their work in the laboratory. They focused on methods to retain Phytophthora zoospores in the filtration process, analyzing the retention ability of porous media such as iron-oxide-coated sand and uncoated sand in a range of solutions at various pH levels.

Zhang said the filters function similarly to household units attached to faucets, but the medium in those filters is typically activated carbon.

The group found that the iron-oxide-coated sand retained zoospores at a greater rate in higher pH solutions. Both the coated and uncoated sand performed well in low-pH solutions. These findings tell researchers that filtering the pathogen can be effective, especially in well-controlled environments — an encouraging sign for greenhouse systems.

A paper on the study was published in the journal Environmental Science and Technology.

To take this newfound knowledge to the applied research stage, the next step was to design and test a small-scale greenhouse filtration system.

The team constructed a water-recycling unit that pumps from a prefilter tank to the filter, which then sends water to a holding tank. Then the filtered water is pumped into the area with the plants on a predetermined schedule. Eventually the water returns to the prefilter tank.

In trials with squash and poinsettias, iron-oxide-coated sand filtration again proved effective, besting both activated carbon and a fungicide treatment with no filter. The results bode well for implementing recycled-water systems, which require less water, fungicides and pesticides.

“We are encouraged by the small-scale trials,” Zhang said. “In the future, it would be nice to get a grower involved to scale it up in a larger greenhouse setting. We will continue to seek the resources to do so.”

Thus far, Zhang and Hausbeck have been pleased with the support they’ve received from a diverse set of organizations. At the outset of the project, they received a $2,500 grant from the Western Greenhouse Association, followed by $10,000 from the Fred C. Gloeckner Foundation. The largest grant came from the American Floral Endowment — three-year funding at a total of $120,000. Zhang and Hausbeck also received support from MSU AgBioResearch to add students to the project.

Partnering with MetaMateria Technologies, a company concerned with water quality, the team operated as a subcontractor on a Small Business Innovation grant from the U.S. Department of Agriculture’s National Institute of Food and Agriculture.

“It has been a great multidisciplinary effort thus far, where we have been able to touch every aspect of the land-grant model and provide potential solutions to problems facing food production in greenhouses,” Zhang said. “We are teaching and providing research opportunities, and Mary has done some outreach. We believe there is definitely room to expand this work moving forward.”

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