Penn State researchers have received federal funding to test whether a nanotechnology device can be used to trap and concentrate plant viruses, with an eye toward providing early detection that could help protect crops from disease and reduce pesticide use.

An interdisciplinary team led by Cristina Rosa, assistant professor of plant virology in the College of Agricultural Sciences, will conduct the two-year project with support from a $325,000 grant from the U.S. Department of Agriculture's National Institute of Food and Agriculture.

A crop plant may look healthy to a human observer while it actually is infected by a deadly plant virus, the concentration of which in the plant's sap is too low to detect. In such a case, the virus' size — only 1/500th the diameter of a human hair — presents a diagnostic challenge. However, the emerging science of nanotechnology, which allows the manipulation of matter at the atomic scale, offers some solutions.

A tomato plant showing symptoms of Tomato spotted wilt disease. With support from a USDA grant, researchers will test a nanotechnology device for its ability to trap plant viruses, facilitating earlier diagnosis of crop diseases. Image: Kaixi Zhao, Rosa Lab

"Our goal is to adapt a nanotechnology micro-device to concentrate pathogens in plants, insects and other organisms so that modern diagnostic procedures can be employed earlier in an infection, when virus levels otherwise may be too low to detect," Rosa said. "This technology will make these diagnostic tools more effective in catching infections at the early stages when growers can manage them more easily and effectively."

The micro-device — known as the carbon nanotube size-tunable enrichment platform, or CNT-STEP — originally was developed by researchers in the Department of Physics in Penn State's Eberly College of Science and the Department of Bioengineering in the College of Engineering. The box-like filtration device contains input and output ports and a "forest" of carbon nanotubes spaced to selectively trap viruses, while liquids and smaller particles pass through.

Capturing these virus particles concentrates them above the detection threshold so the virus can be characterized using diagnostic tools such as polymerase chain reaction, enzyme-linked immunosorbent assay or next-generation sequencing. Researchers already have found CNT-STEP to be effective in capturing previously identified influenza viruses from known concentrations in dilute samples as well as emerging and unknown viruses from field samples.

Scanning electron microscope image (scale bar, 200 nm) of the H5N2 avian influenza virus (purple) trapped inside the aligned carbon nanotubes (Image: Penn State University)

To evaluate the device for use in plant-disease diagnosis, the team will use tomatoes infected with Tomato spotted wilt virus, one of a family of viruses in the genus Tospovirus that infect a variety of crop plants. The value of worldwide yield losses from Tomato spotted wilt has been estimated at more than $1 billion annually.

"Although Tomato spotted wilt virus is a problem in Pennsylvania, it's a more serious disease for growers in Florida and California, which have more acreage in tomatoes and milder winters, which increases the population and survival of thrips, the virus' insect vector," Rosa said. "In Pennsylvania, one problem is that growers might import transplants that already are infected, but they don't know it because the plants are not showing symptoms yet."

In addition, she noted, new strains of the virus are arriving, particularly in Florida, and recombining with existing strains, making these new viruses easy to miss with conventional diagnostics. "Because new or unknown tospoviruses have the same physical properties, this new tool can catch them so they can be concentrated and characterized."

The CNT-STEP device also can be used to trap viruses from insect samples, and because of its small size and portability, it can be used to collect samples in the field for later analysis in the lab.

"We will evaluate the stability of samples collected in the field to ensure that they remain viable until they can be analyzed in the lab," Rosa said. "If so, we believe this tool will be useful for growers, extension specialists and others for early detection and diagnosis as part of an IPM [integrated pest management] strategy."

Such early detection could lead to better modeling of the entire plant-vector disease cycle and could minimize the need for "insurance" insecticide applications, which would reduce environmental impacts, the development of insecticide resistance and costs for growers, she said.

If successful, the researchers will approach diagnostics companies to potentially commercialize the technology, according to Rosa. "We believe it will have utility in a variety of settings, such as in detecting unculturable phytoplasmas and even foodborne pathogens."

Other research team members from Penn State are Beth Gugino, associate professor of vegetable pathology; Ed Rajotte, professor of entomology; Mauricio Terrones, professor of physics, chemistry and materials science and engineering; and Yin-Ting Yeh, postdoctoral scholar in the Terrones lab. Collaborators also include Brenna Aegerter, farm advisor, University of California Cooperative Extension, Stockton, California; and Scott Adkins and William Turechek, research plant pathologists, USDA-Agricultural Research Service, Fort Pierce, Florida.

Source: Penn State University