Sweet orange scab confirmed in an Arizona grove

01/31/2011 02:00:00 AM

By Vicky Boyd
Editor

The U.S. Department of Agriculture's Molecular Diagnostics Laboratory in Beltsville, Md., has confirmed sweet orange scab in a sample taken from a Maroicopa County, Ariz., tangerine grove, according to a North American Plant Protection Organization Phytosanitary Alert.

The confirmation came at the same time the USDA confirmed the disease from three sites in Florida.

In Florida, no sweet orange scab has been found in commercial groves.

The Florida Department of Agriculture and Consumer Services is referring to the organism as "sweet orange scab-like."

Pathologists have compared only a small part of the genome from the Florida sample to that of a Brazilian sample.

Genetically, they match up, says Tim Schubert, administrator of the Division of Plant Industry's plant pathology section.

But symptoms of the disease found in the United States differ from those reported from Brazil.

In that country, the fungal disease causes unsightly, scab-like lesions on the rind of mostly sweet orange cultivars and some tangerines.

So far, symptoms from U.S. sites involve wind scarring-like lesions.

Schubert says pathologist will do further genetic testing to see if the isolate found in Florida could be more closely related to one seen in Korea.

Owners of non-commercial sites where the disease has been confirmed have been issued emergency action notices, which prohibit movement of plant material from the property.

Sweet orange scab, caused by the fungus Elsinoë australis was detected last year in Texas, Louisiana and Mississippi.

The finds in Louisiana and Mississippi involved residential properties, whereas the Texas finds included both residential properties and the commercial citrus area in the Rio Grande Valley.

As a result, the USDA Animal and Plant Health Inspection Service quarantined each of those states.

The agency plans to revise the quarantine to reflect the disease confirmations in Arizona and Florida.

In December, the USDA issued a regulation that allows fruit from groves infested with sweet orange scab to move to citrus-producing states as long as the fruit has undergone approved packinghouse treatments.

Owners of infested groves and packinghouses receiving fruit from those groves also have to be under compliance agreements, which prescribe steps they must take to prevent the spread of the disease.

Those steps include tarping trucks carrying fruit and disposing of culls and plant material following approved methods.



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