The yellow spots on
this leaf are evidence of infection by the Pennsylvania isolate of plum pox
virus. The leaf is from Chenopodium foetidum, an important indicator
species of plum pox disease. Click the image for more information
about it. |
HoneySweet Plum Trees: A Transgenic Answer to the Plum Pox Problem
Frequently Asked Questions
What is plum pox? Plum pox is a plant disease that infects
stone fruit trees including peach, nectarine, plum, apricot and cherries. The
disease, which is also called Sharka (the Slavic name for plum pox) disease, is
caused by the plum pox virus (PPV). It is considered the most serious virus
disease of stone fruit trees. Plum pox is spread from tree to tree by aphids
and through infected budwood used for grafting, which is the normal method of
propagating stone fruit trees. Symptoms of plum pox infection include leaf and
fruit yellowing, fruit deformation, and premature fruit drop. A tree suffering
from plum pox can go into serious decline, especially if the tree also becomes
infected with other viruses.
What does plum pox mean to me as a consumer? Presently, plum
pox is not an issue for consumers. In the U.S., PPV has only been found in a
few places in Pennsylvania and is being eradicated by destroying the infected
and surrounding trees. Pennsylvania is not a major plum-producing area, so the
consumer market for fresh and dried plums in the United States has not really
been affected at this time.
The concern is that if plum pox becomes widespread in the U.S., the
disease could cause a major disruption in the availability of plums, prunes and
other stone fruits if no solution to the plum pox problem is available. So to
ensure that the U.S. consumer continues to have access to the widest variety of
fruit, the Agricultural Research Service began a research program to develop
plum trees with resistance to PPV. More information about plum pox outbreaks in
the U.S.
What is being done to eradicate the PPV infection in the U.S.?
In the U.S., eradication of PPV is done by eliminating infected trees
plus all potentially susceptible trees within a buffer zone around infected
areas. Each buffer zone extends from 500 meters in a circle beyond the
perimeter of an infected area. In a larger zone that extends from 500 to 1,000
meters beyond the perimeters of the first zone is area, 100 percent of the
stone fruit trees also are checked for the presence of the virus.
Plum pox virus is
spread by aphids. Here, Fred Gildow (left), of Pennsylvania State University,
and ARS plant pathologist Vernon Damsteegt set up an experiment to screen
aphids for their ability to transmit the destructive virus. Click the image
for more information about it. |
What is the U.S. Department of Agriculture (USDA) doing about plum pox? The Animal
and Plant Health Inspection Service (APHIS), an agency of USDA, is responsible
for preventing the introduction of plant pathogens into the U.S. All fruit
nursery stock for importation is tested for a range of known fruit tree
pathogens, especially those that are not known to occur in the United States
(exotic pathogens). APHIS plum pox program
What is the Agricultural Research Service (ARS) doing about plum pox?
ARS has an active research
program to develop a better understanding of the virus and how mechanisms of
resistance may work in trees. The primary goal of the research program is to
produce PPV-resistant trees.
Because developing a PPV-resistant plum tree is not a simple or quick
project, ARS has not waited until plum pox has a major presence in the U.S. to
begin research. Rather, ARS has taken the proactive step of developing a
PPV-resistant tree and doing the testing required to allow genetically
engineered trees to become available, before plum pox precipitates a crisis in
this country. (Link: Researchers involved in developing and testing HoneySweet)
How was the PPV-resistant plum developed? ARS researchers
have developed a PPV-resistant tree through genetic engineering. The gene for
the PPV coat protein was separated from the PPV and inserted into a piece of
carrier DNA. This new piece of DNA was inserted into a
bacteriumAgrobacterium tumefaciensthat was used to infect
cells extracted from plum seeds. Seed cells that were found to have
incorporated the new gene into the plum DNA were then regenerated and grown
into complete plum trees. These trees have the new gene in their DNA and are
resistant to PPV.
The new PPV-resistant variety is named HoneySweet.
Symptoms of plum pox
virus on apricot fruit and leaves. Click the image for more information
about it. |
Do you know exactly what new genetic material is in HoneySweet?
Yes, we know all of the genes that have been added to HoneySweet.
Are the added genes in the fruit? Will I be eating foreign genes?
The new DNA is in the fruit. But genes are broken by digestive enzymes in
the stomach. We have analyzed the fruit from HoneySweet and compared it with
fruit from other plum trees, and there is no significant difference in
composition in terms of nutrients usually measured in plums (sugars, acids,
vitamins, fiber, etc.).
Can the virus DNA harm people? Plant viruses do not infect
animals or people. Thousands of infected trees grow in Europe and the fruit
from these trees is eaten by people. There has been no instance of harm from
eating the fruit. Also, a portion of all produce, whether from commercial
growers or the home garden, is infected by various viruses. Such fruit contains
coat protein and coat protein genes from these viruses, and people have always
eaten them. In that sense, HoneySweet is no different than many other fruits
that contain coat protein genes.
Is HoneySweet safe to eat? How do I know that? HoneySweet
will only be released for sale or consumption when its safety is determined by
all three agencies that regulate genetic engineering of crops in the United
StatesAPHIS, the U.S. Food and Drug Adminstration (FDA) and the U.S. Environmental Protection
Agency (EPA). (More information about the genes added to
HoneySweet)
How did you show that the HoneySweet trees are resistant to plum
pox? Trees were tested in a greenhouse for five years. Plant tissue
infected with PPV was grafted onto the new trees, but none of the trees
developed plum pox disease. Trees were also grown in Spain, Poland and Romania,
where PPV is indigenous, and none of the engineered trees have ever been
infected by transmission through aphids, which naturally carry the PPV virus
from tree to tree.
These transgenic plums contain
a gene that makes them highly resistant to plum pox virus. Click the image
for more information about it. |
Have HoneySweet trees been grown in orchards in the United
States? Only one experimental planting has been grown in the U.S.
Permits for this planting were obtained from APHIS, which put very strict
restrictions on how many trees could be grown, where they could be grown, how
far the trees had to be from other susceptible trees, what had to done when the
trees were in blossom, and what had to done with cuttings from the treeto
ensure that test trees were kept under very tight control.
After seven years under strict control, APHIS allowed the trees to
blossom and be pollinated so fruit could be produced. This permission was
granted with the proviso that there were no other stone fruit or other
Prunus species in the area that could be pollinated by HoneySweet.
In addition to the ARS research location where HoneySweet was developed,
the trees have been grown in Spain, Poland and Romania under restrictions
specific to each country.
Could HoneySweet pollinate other trees? HoneySweet will cross
with other domestic plum trees.
To find out how far HoneySweet plum pollen will travel to other plum
trees, almost 3,000 seeds were evaluated over six years at distances from 230
to more than 3,500 feet from the HoneySweet planting. Over the six years of
testing, only two seeds were found to have received HoneySweet pollen. These
were at a distance of about 1,700 feet from the HoneySweet trees. (More information about
pollination and crossbreeding )
ARS horticulturist
Ralph Scorza. Click the image for more information about it.
|
Have APHIS, EPA and FDA approved the release of HoneySweet?
APHIS recently "deregulated" HoneySweet, which means APHIS has made a determination that the organism is not a plant pest and found that it will have no significant impact on other plants. Deregulated products have an established history of safe use in U.S. agriculture, and APHIS has the authority to bring any deregulated item back under regulation if new information becomes available that demonstrates unanticipated effects or risks to plant health. APHIS has been safely regulating GE organisms since 1986 and has overseen the deregulation of over 70 GE plants, including corn, cotton, rapeseed (canola), soybean, flax, sugar beet, squash, and papaya. Soybeans, corn, cotton, and canola that are herbicide tolerant or insect resistant are the most frequently planted deregulated crops.
With deregulated status, HoneySweet and its progeny can be freely moved and planted without the requirement of permits or other regulatory oversight by APHIS. HoneySweet is the second tree to be deregulated by APHIS. In September 1996, papaya became the first tree to be deregulated.
ARS has also submitted information to FDA and an application has been filed with EPA for HoneySweet to be registered as a plant incorporated protectant (PIP). EPA regulates PIPs—which are mainly pesticide-like proteins produced in plants—as new uses of herbicides and pesticides on plants.
Am I likely to see HoneySweet plums in my grocery store soon?
People are not likely to see these plums and prunes in stores anytime
in the near future. Plum pox is still being contained and eradicated at this
time. But as with most foreign diseases, there is the potential that plum pox
will become established in the U.S., and all of our current plum tree varieties
are susceptible. Since it takes years to develop and multiply new varieties, we
can't wait until the problem becomes endemic to do the research to have
resistant trees. USDA needs to be ready before the problem becomes a crisis.
(More information about
how HoneySweet is expected to be used)
Is ARS consulting with plum growers and the nursery industry about
the planned release of a genetically engineered (GE) plum? Research
horticulturalist Ralph Scorza, who has been heading ARS's research program,
spoke about his research on this plum and the planned deregulation at the
International Fruit Tree Fruit Association (IFTA) meeting in February 2006 in Hershey,
Pa.. He will be consulting with grower and industry groups in the near future
as HoneySweet nears release. More information for the plum orchard industry
Where can I get more information about HoneySweet
development and ARS plum pox research? Contact Kim Kaplan, ARS
Information Staff, 301, 504-1637, Kim.Kaplan@ars.usda.gov.
Links to information about plum pox from
Links to information about agricultural genetic engineering
from
|