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Zinkicide Could be a Benefit, but There's No Guarantee

The Ledger – May 5, 2015

ORLANDO | It comes in a small package that could become a big gift to Florida citrus growers.

Zinkicide is a nanoparticle, a substance as small as a DNA molecule, that is being tested as a possible bactericide against citrus greening, the deadly bacterial disease threatening the future of Florida’s commercial citrus industry.

“It’s a hundred-year-old disease, but to date there is no cure. It’s a killer, a true killer for the citrus industry,” said Swadeshmukul Santra, associate professor in the NanoScience Technology Center at the University of Central Florida, one of a team of 13 scientists from six research organizations testing the effectiveness of Zinkicide against greening.

The five-year, $4.6 million research program is just in its first year, and there’s no guarantee of success, he told The Ledger last week.

“I fully understand (the citrus growers’) pain. I don’t want to give false hope to anyone,” said Santra, who’s been working on nanoparticle technology, initially for computer semiconductors, for more than 15 years.

Scientists have known about zinc nanoparticles for many years, he said, and they’ve been used for tires and paint pigments in addition to semiconductors.

Santra got involved in agricultural uses in 2009, when he collaborated with Jim Graham, a soil microbiologist at the University of Florida’s Citrus Research and Education Center in Lake Alfred, he said. They were working to develop alternatives to copper sprays for citrus canker, another bacterial disease that was the major threat to Florida citrus before greening surfaced in 2005.

Santra invented Zinkicide, which as the name suggests is a formulation of the chemical element zinc, he said. Other than identifying it as a nanoparticle, he declined to discuss its properties.

Zinkicide’s size offers a major advantage over other chemical bactericides also being researched in the greening battle, Santra said. A large molecular size can prevent some chemicals from moving around the tree’s vascular system, called the phloem.

Zinkicide appears to move freely through the phloem and attacks the greening bacteria inside tree cells, he said.

“The bacteria hide inside the plant in the phloem region,” Santra said. “If you spray and your compound doesn’t travel to the phloem region, then you cannot treat (greening).”

Another potential advantage for Zinkicide is that it can be applied as a leaf spray or soil drench, he said. The best application method and its timing are part of the research program.

Other potential bactericides must be injected into the tree trunk or have more costly, less efficient applications.

“The biggest challenge is: Will it kill the bacteria?” said Harold Browning, chief operating officer at the Citrus Research and Development Foundation in Lake Alfred, which is leading the greening research effort. “The next biggest challenge is how to apply it.”

Zinkicide is one of more than a dozen potential greening bactericides being explored currently, he added.

Even if Zinkicide proves effective in less time than the projected five-year program, it still faces regulatory approval before it can be released to growers, Browning and Santra said.

At the federal level, agencies including the USDA, the Environmental Protection Agency and the Food and Drug Administration, or any combination, would be involved, Browning said.

“People who tell you they can predict how long regulatory approval will take don’t know what they’re talking about,” he added.

One possible advantage of Zinkicide is that regulators could classify it as a “bio-agent,” which could shorten the approval process, Browning said.

Money for the Zinkicide project comes from the U.S. Department of Agriculture as part of its five-year, $125 million research program to find new solutions to greening. The Zinkicide project was the largest grant awarded among the $23 million handed out in the first year of funding.

Also on the research team are scientists from the Lake Alfred center, Oak Ridge National Laboratory and the universities of Auburn, New Mexico State and Ohio State.

Polk leads the state’s citrus-producing counties with 81,810 grove acres and 10 million trees in 2014, according to U.S. Department of Agriculture data. It historically leads the state in citrus production, as it did in the 2013-14 season with nearly 19.9 million boxes harvested.

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