Nick Rajtar develops new tools for closing in on evasive tree pathogens in the field and in the lab.
October 26, 2021
by CAROLYN BERNHARDT | MITPPC communications specialist
Emerald ash borer (EAB) is more than meets the eye. It turns out, the way EAB manages to kill trees is just as complicated as the labyrinthine markings the beetle leaves behind. Nickolas Rajtar—a PhD student in the lab of Robert Blanchette, a professor in the Department of Plant Pathology in the College of Food, Agriculture and Natural Resource Sciences—is unsnarling the twisty-turny mess of EAB by taking a closer look at the fungal communities that trail behind the pest.
Catching a culprit in the act
The Blanchette Lab and Rajtar started by investigating fungi in the galleries EAB creates in wood, just beneath a tree’s bark. Sampling trees in the Twin Cities, Duluth, and Rochester, Rajtar and collaborators grew out fungi they isolated from EAB galleries. Then, the team extracted and sequenced the fungi’s DNA to better understand the genera and species of fungi they collected. The researchers came away with 1,126 species of fungi creeping upon EAB in the galleries.
The team is publishing a paper on their findings shortly, Rajtar says. “What we suspected and found was that canker fungi were the most abundant of all fungi isolated.” According to Rajtar, canker fungi work in concert with EAB and help contribute to the mortality of each infected tree. “I did a literature review and selected the fungi from those we isolated that would be the most likely to cause these cankers on ash trees, grew those out, placed them in ash saplings, harvested the saplings after a year, and measured the lesions they left in the trees.” Pinpointing which canker fungi communities associated with EAB are causing the most harm to trees and understanding their genetics can help researchers identify new management strategies for stopping EAB in its tangled tracks.
The EAB research also helped Rajtar grow as a scientist. “I really got to hone my molecular skills throughout the project,” he says. “I have also learned to collect samples from trees more efficiently — I can more easily find the right part of the tree to sample depending on the pathogen.” So, while EAB’s reach seems to be ever-expanding, so too are the techniques of the scientists tracking it down. The project’s methods in the lab, Rajtar says, also set the groundwork for the biosurveillance research he is currently doing.
New tactics, new targets
Now, Rajtar is tracking down Heterobasidion irregulare, also called Heterobasidion Root Disease (HRD), across Minnesota. The invasive tree pathogen is yet another fungus. Recently harvested pine plantations near infection zones are most at risk for disease. HRD spreads through the landscape through airborne spores or root grafts underground. Once this pathogen establishes in a stand of trees, Rajtar says, it is nearly impossible to eradicate. And it’s rampant across Wisconsin.
Rajtar started his biosurveillance project by testing three different technologies for trapping HRD spores. Each spore trap runs the gamut in terms of cost, but Rajtar found that the accuracy of their results was fairly similar. That means, researchers can use the more expensive tech in places where they already know Heterobasidion exists, and start with the more affordable models in places where they suspect the pathogen’s presence.
Rajtar is also sequencing the DNA of the spores he’s trapping. He’s trying to map the pathogen’s spread from the Wisconsin border across Minnesota. “The Wisconsin forest systems are getting hammered with Heterobasidion, and little to no action was taken when the fungus was identified in Wisconsin in the 1990s. We don’t want that outcome for Minnesota. We want to detect it before it establishes here,” Rajtar says. He wants to help equip managers and researchers with the tools they need to hit back. “If we have alarming findings, we can recommend the DNR take certain actions.”
Chasing down a “plant destroyer”
Rajtar is also looking into biosurveillance methods for Phytophthora, a genus of water mold whose name translates to “plant destroyer” in Greek. The water mold (or oomycete) damages crops and forest systems and negatively impacts food security. Before Minnesota becomes overrun with invasive fungi or oomycetes, Rajtar would like to identify affordable, sustainable methods for biosurveillance of these invasive species.
As another part of the project, Rajtar and his collaborators are monitoring trees in nurseries across Minnesota. Some larger Minnesota nurseries grow their plants in-house, but ship their trees in from out of state. “We want to make sure there are no pathogens circulating in our nurseries,” Rajtar says. “Or, if they are, we want to identify them and make sure we catch them before they get out into the forest system, or the landowner spreads it around the neighborhood.” It’s Rajtar’s second year sampling at nurseries. Last year, he found some pathogens. This year, however, he is unearthing Phytophthora in nursery and forest settings.
The future of biosurveillance
Minnesota doesn’t have a biosurveillance team for forest pathogens but Rajtar hopes his research lays the groundwork for one. Other researchers in other states could also model after his approaches, too.
Funding from the Minnesota Invasive Terrestrial Plants and Pests Center (MITPPC) helped Rajtar investigate EAB and transition his work from a master’s to a PhD program. During that time, he had two years of funding from the center. Now, he has four additional years of funding from MITPPC to close in on Heterobasidion and refine biosurveillance tactics for researchers across the state.
But ultimately for Rajtar, it’s personal. “Without the funding, there would be a lot more invasive species in Minnesota,” Rajtar says. “I grew up in Minnesota and I want people to enjoy the forests for generations to come. MITPPC is really helping to detect invasive species and keep them at bay.”