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USDA Scientists Develop New Test For Fruit Tree Viroids

July 7, 1993

WASHINGTON (AP) _ Agriculture Department scientists have developed a speedy new test to detect disease-causing overseas viroids, viruslike micro-organisms that can devastate apple and pear trees.

″Now new apple and pear trees coming into the U.S. can be grown in a greenhouse for just two months. And then screening them for apple scar skin viroid takes just about a day or two using our new test,″ said plant pathologist Ahmed Hadidi of the Agricultural Research Service.

Viroids are the world’s smallest infectious agents and some of the toughest to identify. They were discovered by an Agriculture Department scientist in 1971. Other diseases can mask symptoms of viroids.

Hadidi said the new test is three to five years faster than the current practice of waiting for the tree to bear fruit and then looking for symptoms of apple scar skin viroids such as spotting and scarring of fruit.

Apple scar skin viroid takes the longest time to identify and confirm, Hadidi said.

Hadidi said a faster test could mean that growers and consumers may not have to wait as long for a new fruit variety that owes its flavor to an imported species.

″We’ve seen prime candidates for new species, such as Chinese pears of superior flavor and market value, that must spend years in quarantine,″ he said.

After USDA’s Animal and Plant Health Inspection Service approves the new technique, it will be used to screen plants at federal quarantine centers, Hadidi said.

″A foreign species - in fact, all incoming plants - undergo quarantine so no viroids or other disease-causing pathogens accidentally enter the country,″ said research associate Edward V. Podleckis, who is working with Hadidi at the National Germplasm Resources Laboratory in Beltsville, Md.

Apple scar skin viroid, which infects some fruit trees in China and Japan, is spread by grafting from infected cuttings. Podleckis spent several months developing and perfecting a tissue blot test for the viroid.

The test starts with a viroid-free plant. Podleckis grafts onto it a piece of the quarantined plant.

When the plant has grown for two months, he takes a twig or leaf from its new growth and presses it down on a wet filter so some sap sticks to it. Then he uses a non-radioactive probe to produce light that, when placed next to the filter, exposes a piece of photographic film. A dark spot appears wherever apple scar skin viroid is present.


WASHINGTON (AP) - The U.S. Feed Grains Council is celebrating the 20th anniversary of its Taiwan office, which it says has resulted in more than 5 million metric tons of grain being shipped to that country annually for the past four years.

″From the beginning of our joint endeavors in 1973, with the opening of the official USFGC office in Taipei, a trade relationship of trust and commitment has served to benefit both our countries,″ said Charles Ottem, council chairman.

Agriculture Secretary Mike Espy sent a letter congratulating the council on the anniversary.

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