New Survey Method Adapted to Detect Plum Pox Virus

A new sampling method to more accurately detect plum pox virus (PPV) has been adapted by Agricultural Research Service scientists. This method will be used in the U.S. Department of Agriculture’s $1.4 million national PPV surveillance program. ARS is the USDA’s chief research agency.

PPV was first detected in 1999 on peaches grown in an Adams County, Pa., orchard. This viral disease infects stone fruit species including peaches, plums, apricots and nectarines, as well as almonds. PPV infestation produces blemished, misshapen fruit and causes fruit to drop prematurely. It can even prevent a tree from bearing any fruit at all. The value of U.S. stone fruit production was $1.3 billion last year.

ARS plant pathologist Timothy R. Gottwald, with the U.S. Horticultural Research Laboratory in Ft. Pierce, Fla., and Gareth Hughes with the University of Edinburgh in Scotland, have adapted the hierarchical sampling (HS) strategy they developed for citrus tristeza virus to more accurately sample large areas for PPV.

Previous sampling methods used for citrus and other crops are based on the number of infested soil samples, disease lesions on a leaf, proportion of diseased fruit or the number of insects found on each plant.

The problem with using these strategies for PPV is that the amount of the disease in any given tree cannot be quantified. A PPV-infected tree may be showing many symptoms or very few and still be entirely infected.

HS also relies on the theory that it’s possible to predict disease in one location by sampling at another. By sampling only 6.25 percent of the trees in a given orchard in groups of four trees--the location of the trees in the orchard is critical--and crunching the numbers, scientists are able to accurately predict the incidence of infection in the whole orchard.

After performing thousands of simulations, Gottwald and Hughes have shown HS to be much more accurate at detecting plum pox virus infestation than other sampling methods.

Scientific contact: Tim R. Gottwald, ARS U.S. Horticultural Research Laboratory, Ft. Pierce, Fla.; phone (407) 897-7347, fax (407) 897-7309, tgottwald@ushrl.ars.usda.gov.