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New Test to Improve Plum Pox Monitoring in Stone Fruit

By Jan Suszkiw
October 3, 2003

Monitoring the spread of the plum pox potyvirus in stone fruit crops could get a lot easier with a new, genetic fingerprinting test developed by Agricultural Research Service scientists.

Plant pathologist Bill Schneider and colleagues in the ARS Foreign Disease-Weed Science Research Unit at Fort Detrick, Md., developed the test to expedite year-round plum pox monitoring in and around Pennsylvania's Adams, Cumberland, Franklin and York counties--the only U.S. sites where the stone fruit disease is known to occur.

The aphid-borne disease causes acidity, unsightly rings and other defects that diminish the quality of peaches and other stone fruit. Plum pox poses no consumer danger, but it casts a threatening cloud over the economic well-being of the nation's $1.8 billion stone fruit industry.

As part of an eradication effort, Pennsylvania researchers collect thousands of leaf samples annually from commercial orchards, nurseries and other sites for analysis in diagnostic labs. But plum pox only shows up at certain times of the year, and in certain parts of a host tree, which complicates the process. During the summer, for example, viral counts plummet as temperatures hit 84 and 90 degrees Fahrenheit. When that happens, antibody-based tests, such as the Enzyme-Linked Immunosorbent Assay (ELISA), can yield misleading results. Other methods are time-consuming and labor-intensive.

The new, ARS-developed test uses real-time polymerase chain reaction (PCR), a chemical procedure that mass-produces copies of specific genes or gene fragments so they can be identified. With real-time PCR, the targeted gene becomes detectable as it's being multiplied. In this case, the gene is for a specific protein that makes up the outer coat of the virus. Scientists generally can determine whether the protein is in a sample in about six hours--and if so, they can learn how much virus is in the sample. The ELISA methods, by comparison, take about a day.

A longer article about this research appears in the September issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture's chief scientific research agency.