Recycle water, not pathogens

The capture and reuse of water for irrigation is a vital part of many nursery and greenhouse operators’ efforts to make their business economically and ecologically sustainable. However, this practice could spread destructive plant pathogens throughout an entire facility in a very short time.

Several researchers have been studying this issue to as part of a USDA-funded project to find a way for nurserymen and greenhouse operators to recycle irrigation water without recycling plant pathogens.

The project, “Integrated management of zoosporic pathogens and irrigation water quality for a sustainable green industry,” is a $2.7 million project funded by the USDA Specialty Crops Research Initiative for 2010-2015.

The goal of the project is to learn more about Phytophthora and Pythium in recycled irrigation water so that effective measures can be put into place by nurserymen and greenhouse operators to eliminate these important plant pathogens from their production systems. The researchers are looking at the presence of plant pathogens in recycled irrigation water as a serious water quality issue about which growers and scientists know relatively little.

“We want to educate growers and other scientists to the fact that these pathogens can be accumulated in recycling systems and then dispersed to the crops being irrigated,” said Dr. Gary W. Moorman, professor of plant pathology at Penn State University.

The idea for the project came from a collaboration between Moorman and Dr. Chuan Hong, professor of plant pathology at Virginia Tech. Hong had already been looking into Phytophthora in nursery irrigation water. Moorman, who was on study leave at Virginia Tech’s field station in Virginia Beach, had expertise on Pythium, primarily a greenhouse problem. They worked together on a research proposal along with John Lea-Cox at the University of Maryland and several others at Virginia Tech, USDA, and others. The proposal was submitted to the Specialty Crops Research Initiative of USDA and received funding for five years (2010-2015).

Hong’s team continues to work on the detection and identification of Phytophthora in nursery water and Moorman’s lab is working on the detection and identification of species of Pythium in commercial greenhouses.

Findings
In the greenhouses where Moorman’s group is doing research, they’ve found that the major plant pathogenic species of Pythium are not, in fact, commonly found in the water being recycled. There are many other species of Pythium present, some new to science, but these common water inhabitants are not pathogenic.

“We believe that the bacteria naturally found in the irrigation water are suppressing the plant pathogenic Pythium species,” Moorman said. “We hope to characterize these bacteria and determine what can be done to foster their survival and activity in recycled irrigation water.”

In his research, Hong is finding many species of Phytophthora in irrigation water, several of which are new to science. He has documented that the water just returning to the reservoir after irrigation can have a great deal of Phytophthora. But when the water is sampled far from where the runoff enters, there is much less Phytophthora. Based on that, he is recommending that growers place the pump intake as far from the runoff inlet as possible. He too is looking at the natural populations of bacteria in the nursery water to determine if they suppress Phytophthora while it is being held in the reservoir.

“We’re really right in the middle of the research,” Moorman said. “Like most science, we end up asking more questions than we answer, and that’s the stage we’re in right now.”

The research is in collaboration with Hong, Ping Kong, Kevin K. Boyle, Darrell Bosch, Boris Vinatzer, and James Pease (Virginia Tech), John Lea-Cox (University of Maryland), Warren Copes (USDA, Poplarville, MS), Gladis Zinati (Rutgers University), and Edward Weiss (Christopher Newport University).

Moorman said he and the rest of the research team are in the process of developing other best management practices that growers can institute in their existing production systems.

Also, they are writing a book on the topic of plant pathogens in irrigation water. Nearly 40 authors from all over the world have contributed chapters to the book, which is aiming to be published this July by the American Phytopathological Society.