New Survey Method Adapted to
Detect Plum Pox Virus
June 21, 2000
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 Agricultures $1.4 million national PPV surveillance
program. ARS is the USDAs 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
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 its 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
Scientific contact: Tim R. Gottwald, ARS U.S. Horticultural Research
Laboratory, Ft. Pierce, Fla.; phone (407) 897-7347, fax (407) 897-7309,