Skip to main content

U.S. flag An official website of the United States government

Animal and Plant Health Inspection Service
U.S. Department of Agriculture
USDA FAQ's and resources about coronavirus (COVID-19).  LEARN MORE

Background Information on Potential Data Requirements for Environmental Assessments of Trees and Woody Plants

Biotechnology Meetings



Genetically Engineered Forest and Fruit Trees Public Meeting
July 8-9, 2003


Discussion Questions

Since the first genetically engineered plants were field-tested in the 1980's, USDA/APHIS has gained considerable experience in assessing such plants for agricultural and environmental safety. Most of APHIS' experience, however, has been with annual row crops and the agency recognizes that the issues and data needs may vary for other types of plants, such as trees and other perennial woody plants. This is especially true when APHIS must assess the risks associated with commercial release (i.e., a petition for nonregulated status).

Applicants requesting a determination of nonregulated status for a plant (under 7 CFR 340) must provide information on the intended phenotype and any unintended or unanticipated traits. The transgenic plant should be compared to its closest counterpart(s) and related cultivated varieties, as appropriate. APHIS' experience with previous petitions for determination of nonregulated status has demonstrated that the transgenic and closest comparators are highly similar in phenotype and evaluated characteristics. However, minor differences are not uncommon and the comparison with related varieties allows an assessment of whether characteristics of the transgenic fall within a range of general standards. If grafted plants are used for evaluation, they should be compared to grafted plants utilizing the same rootstock. The applicant should address any detected phenotypic changes in their submission.

Typically, observations on plants are made from several sites over several growing seasons. Testing locations should be generally representative of normal growing regions for the species. Where there may be a potential for increased weedy or invasive characteristics or species outcrossing, it may also be appropriate to evaluate the plants outside of the typical managed ecosystem. In some cases, additional studies may be warranted to provide the required information. Applicants may provide valid scientific rationale why certain information requirements are unnecessary or inappropriate.

Section I below contains questions relating to a number of overarching issues relevant to transgenic trees. Section II contains a list of characteristics which may be important for detecting differences in plant phenotype that may result from the introduction of new genes.

I. Overarching questions of a general nature:

Gene Flow

A major issue focuses on the escape of genes from the transgenic into sexually compatible species outside a managed site.

1. Are there recommended methods to evaluate gene flow issues? What are those methods? Are there particular genes that would be more suitable than others for this work?

2. Would the use of plant or seed sterility systems be useful in some cases? Which cases would those be? Are there other strategies that would also be useful to address gene flow issues?

3. Assuming that genes without increased fitness characteristics may persist in the environment, should APHIS evaluate the impacts of this and if so, how should this be accomplished?

4. Other than the following: outcrossing frequency, compatible species, known hybrids, weedy or invasive nature of compatible species, are there other parameters related to outcrossing that should be evaluated?


Some of the evaluation characteristics are designed to evaluate changes to a plant's propensity to grow or reproduce more quickly than its progenitor.

5. Other than seed characteristics of production, dormancy, emergence and viability, are there other seed parameters that should be evaluated?

6. How could the spread of herbicide resistance genes into compatible species of trees of interest affect weed populations and weed management options?

Other Issues

7. What research tools are available to extrapolate results obtained from controlled field trials over relatively short time frames to large scale plantation and orchard plantings?

8. Are greenhouse and/or growth chamber tests sufficient for some of the recommended traits?

9. How should APHIS evaluate the impact on ecosystems resulting from introduction of plants with pesticidal properties and the likely development of resistant pests?

10. Is the non-transgenic progenitor organism the appropriate comparator in all cases? If not, what would be the appropriate comparator?

II. List of proposed characteristics for evaluation:

After discussion of the questions in BOLD below, breakout groups should provide input on the recommended minimum number of testing locations and years required for data collection. Parameters might include managed and unmanaged sites, and within and outside the typical geographic range for the species.

(Breakout discussion groups should address questions in BOLD type).

1. Stress adaptations -

Applicants should note responses to those stresses observed.

a. Biotic factors - parasites, pathogens, competitors, herbivores, etc.

b. Abiotic factors - water stress, nutrient deficiencies or other stresses common to the species.

• What types of studies should be conducted to determine if there have been any effects on stress adaptations in transgenic trees (both biotic and abiotic)?

2. Hardiness - Hardiness zone information - A significant predictor of invasive success of a species is a wide latitudinal range (Reichard, 1997). If the cold hardiness of a plant changes as a result of gene introduction, this could result in an increased growth range. Evaluating cold hardiness of woody plants is not easy to determine. Both field and laboratory evaluations, however, can be made that give good indications of this character (E. Ashworth, personal communication)

a. Field evaluation of terminal buds - The date that a plant sets a terminal bud and the date at which the terminal bud breaks are indicators of the plant entering and breaking dormancy.

b. Tissue hardiness - Determinations of hardiness should be made at several times during the cold season. Woody tissue is collected from the field, chilled to different temperatures in the laboratory and testing is done (differential thermal analyses, electrolyte leakage, etc.) to determine tissue injury at different temperatures.

• Are these the appropriate measures to critically evaluate plant hardiness? Are there other methods that would be appropriate?

3. Symbionts -

Applicants should provide information on effects on associated organisms (e.g., mycorrhizae or others).

• What types of studies should be conducted to determine if there have been any effects on symbiont organisms?

4. Life span-

Applicant should note and record whether the presence of the introduced gene(s) has produced changes that affect the fitness of the plant such that plants have or may have a longer or shorter useful life span.

• Has the presence of the introduced gene(s) affected the fitness of the transgenic plant? If so, how?

• Are there recommended methods for obtaining this data?

5. Growth habit-

Applicant should note and record changes in basic morphology and plant architecture including any abnormalities (minimum evaluation once a year).

• Are there changes in basic morphology and plant architecture compared to the non-transgenic control?

6. Vegetative vigor-

Two characteristics that are often associated with increased potential for “weediness” are rapid growth and vigorous vegetative reproduction (Baker, 1974). Applicant should note and record aspects of plant vigor appropriate to the species being evaluated (plant height, trunk diameter, wood weight, number of suckers, etc.) (minimum yearly or as appropriate).

• Is the transgenic more or less vigorous than its non-transgenic counterpart?

7. Number of years to maturity - A shortened juvenility period (defined as period from seed germination to the onset of reproduction) has been associated with increased potential for invasiveness (Reichard, 1997).

Applicant should provide data on seed/fruit production relating to quantity and quality as they compare to the standard.

a. When does the tree first flower? Is this earlier or later than the standard?

b. When does the tree first set fruit? Is this earlier or later than the standard?

8. Disease and insect resistance/susceptibility -

Applicant should provide several years of data from multiple locations.

a. What are the typical disease and insect problems associated with the tree (or other woody plant) at the various locations?

b. Are the transgenics more or less susceptible to the typical diseases/insects or new diseases/insects?

c. How does the transgenic compare to the non-transgenic standard?

9. Pollen parameters -

Applicant should provide information on several aspects of pollen production and how they compare with the standard at all test locations. More pollen production or a higher proportion of viable pollen has the potential to increase gene flow.

a. Is the amount of pollen produced the same?

b. Is the proportion of viable pollen the same?

c. Is the pollen viability changed under varying environmental conditions?

d. How long is the pollen viable?

e. Are physical parameters of pollen changed (e.g., size, stickiness, weight, shape) such that they might affect the viability or performance of the pollen?

10. Impact on pollinator or other associated species -

Applicant should provide information on any aspect of the plants that might affect main associated species (bees, birds, mammals, etc.)

a. Has there been a change in flower morphology, color, etc. such that pollinator species have changed or become less or more frequent?

b. Have flower/fruit characteristics resulted in change in habit of other species (e.g., birds or mammals)?

11. Seed dispersal factors -
Seed dispersal is one of the traits that is used to evaluate the potential for weediness in plants (Hancock and Hokanson, 2001). Applicant should provide information on any characteristics of seed development (e.g., shattering, splitting, etc.) that might affect how seeds are dispersed.

12. Seed parameters -

Several characteristics associated with plant seeds affect how invasive a species might become (Baker, 1974). Applicants should provide information on several aspects of seed/fruit production and how they compare with the standard.

a. Production -

• Do the plants produce more or fewer seeds than the standard?

b. Seed dormancy - Many seeds have requirements for breaking dormancy prior to germination (cold, moisture, etc.).

• Do seeds have dormancy requirements that differ from the standard?

c. Seedling emergence -

• Does an evaluation of seed germination under a variety of conditions reveal differences from the standard?

d. Seed viability -

• How long do seeds remain viable under “typical” field conditions?
• Are there any other changes in fruit set or seed production and growth that are different from the standard?

13. Outcrossing-

Several of the most utilized tree species readily hybridize within their genera (e.g., Prunus, Pinus, Populus, Malus). Applicants should provide information on outcrossing with compatible species.

a. Does the species outcross and if so, what is the frequency and with what other species?

b. Are hybrids and introgressed plants known (list and give characteristics) and how do they compare with the standard? Are they either more or less fit than the comparator?

c. Are compatible species known to occur in areas adjacent to typical plantings?

d. Are compatible species known to be weedy or invasive?

14. Self compatibility has been noted to be significantly more common in invasive species than non-invasive ones (Reichard, 1997).

• Has the character of self-compatibility changed from the non-transgenic standard?

15. Fruit maturity and ripening -

Fruit trees cultivars have known dates over which their fruit typically ripen. Although these absolute dates are different from season to season based on environmental conditions, they should not vary significantly from an adjacent standard. Applicant should provide data on how ripening dates compare with the non-transgenic standard and if ripening is more or less uniform than the standard.

16. Fruit yield -

Applicant should provide several years of data demonstrating how the transgenic trees yield compare with the non-transgenic standard. This would typically include lbs/tree or similar measure.

17. Fruit quality -

Applicant should provide several years of data demonstrating how fruit quality compares with the non-transgenic standard. Typical measurements include soluble solids, acids, pH, flavor, texture, etc., as well as post harvest/storage evaluations for mealiness, browning, etc.

18. Wood quality/chemistry (trees for wood harvest only) -

Applicant should provide data on typical measurements of wood quality (lignin, pulp quality, etc.) and how they compare with the non-transgenic standard.


Baker, H.G. 1974. The Evolution of Weeds. Ann. Rev. Ecol. Syst. 5:1-24

Reichard, S. E. 1997. Prevention of Invasive Plant Introductions on National and Local Levels. In; Assessment and Management of Plant Invasions, eds. Luken, J.O. and Thieret, J.W. pp 215-228.

Hancock, J.E. and Hokanson, K.E. 2001. Invasiveness of Transgenic vs. Exotic Plant Species: How Useful is the Analogy? From; Proceeding of the First International Symposium on Ecological and Societal Aspects of Transgenic Plantations, eds. Strauss, SH and Bradshaw, HD. pp 187-192.



Complementary Content