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Plant Pest Risk Assessment for DP-32138-1 Corn

Pioneer Hi-Bred International, has petitioned APHIS (APHIS number 08-338-01p) for a 

determination that genetically engineered (GE) corn (Zea mays L. subsp. mays) event 

DP-32138-1 is unlikely to pose a plant pest risk (Pioneer 2009) and, therefore, should no 

longer be a regulated article under APHIS’ 7 Code of Federal Regulations (CFR) part 

340. APHIS administers 7 CFR part 340 under the authority of the plant pest provisions 

of the Plant Protection Act of 20001. This plant pest risk assessment was conducted to 

determine if DP-32138-1 is unlikely to pose a plant pest risk. 

DP-32138-1 was produced by transformation of a developing corn embryo of line H-II

using A. tumefaciens. Because A. tumefaciens is a plant pest and some of the regulatory 

sequences (Cauliflower Mosaic Virus enhancer) used to facilitate expression of these 

genes in corn were derived from plant pests, this corn has been considered a regulated 

article under APHIS regulations at 7 CFR part 340.

Potential impacts to be addressed in this risk assessment are those that pertain to the use 

of DP-32138-1 and its progeny in the absence of confinement. APHIS utilizes data and 

information submitted by the applicant, in addition to current literature, to determine if 

DP-32138-1 is unlikely to pose a plant pest risk. If APHIS determines that a GE organism 

is unlikely to pose a plant pest risk, then APHIS has no regulatory authority over that 

organism. 

Potential impacts in this Plant Pest Risk Assessment are those that pertain to plant pest 

risk characteristics. APHIS regulation 7 CFR 340.6(c) specifies the information needed 

for consideration in a petition for nonregulated status. APHIS will evaluate information 

submitted by the applicant related to plant pest risk characteristics, disease and pest 

susceptibilities, expression of the gene product, new enzymes, or changes to plant 

metabolism, weediness of the regulated article, any impacts on the weediness of any 

other plant with which it can interbreed, and transfer of genetic information to organisms 

with which it cannot interbreed. 

The Environmental Assessment (EA) for this petition considered whether agricultural or 

cultivation practices for DP-32138-1 may result in impacts on the environment. A 

thorough assessment of the effects of the determination on non-target and beneficial 

organisms, and threatened and endangered species is included in the Environmental 

Assessment.

Development of Male Fertility/ Male Sterility DP-32138-1 Corn

 

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Section 403 (14) of the Plant Protection Act (7USC Sec 7702(14) defines plant pest as:

“Plant Pest - The term “plant pest” means any living stage of any of the following that can directly or indirectly injure, cause damage 

to, or cause disease in any plant or plant product: (A) A protozoan. (B) A nonhuman animal. (C) A parasitic plant. (D) A bacterium. 

(E) A fungus. (F) A virus or viroid. (G) An infectious agent or other pathogen. (H) Any article similar to or allied with any of the 

articles specified in the preceding subparagraphs.” 
2

Since the 1930s, corn productivity in the U.S. has been greatly enhanced by the use of 

hybrid corn seed (Sleper 2006). Corn hybrids are characterized by increased resistance to 

diseases and enhanced agronomic characteristics compared with the parental lines 

(Brewbaker 1964). The production of hybrid corn seed involves a cross between two 

inbred lines2, where the pollen from the tassel/male parent is used to fertilize the 

ear/female parent. Because corn is mostly self pollinated (OECD 2003), hybrid corn seed 

is typically produced by the removal of male flowers (tassels) from the female parent 

either mechanically or by hand. However, mechanical detasseling can result in up to 40 

percent reduction in seed yield when compared to that of hand detassel treatments (Wych 

1988). In addition, female plants may be blown over by a storm and escape detasseling, 

allowing secondary tassels to develop after completion of the manual detasseling. In 

either case, some of the female plants will be self-pollinated resulting in seed of the 

female inbred being harvested along with the hybrid seed.

As an alternative to tassel removal, numerous genetic strategies have been attempted to 

achieve male sterility3(Skibbe 2005). Over 40 genetic elements are associated with male 

sterility. Some of these elements are located on the nuclear chromosomes while others are 

located on the mitochondrial chromosomes (Skibbe 2005). A major drawback to male 

sterile genetic approaches is the difficulty in generating male inbred lines because no 

functional pollen is produced in a male sterile plant line.

Pioneer has developed a novel method (Pioneer 2009, Appendices 1 through 7) that uses 

DP-32138-1 to produce male sterile/female inbred plants for the generation of hybrid 

corn seed that is non-transgenic (known as “Seed Production Technology”, Pioneer 2009,

pp. 23- 26, figures 3, 4 & 5). As detailed in the petition, the carefully controlled 

expression of a seed color marker gene and pollen fertility and sterility genes facilitates

the generation of red transgenic seed for seed increase of male sterile-female inbred lines,

and for the production of non-transgenic fertile pollen for use in non-transgenic hybrid

seed production (Pioneer 2009, figure 3, 4 & 5). 

DP-32138-1 lines are used to produce male sterile female inbred lines and are not used 

for commercial production of commodity corn (Pioneer 2009, pp. 23, 101, 122-123). The 

total acreage in the U.S. planted each year with DP-32138-1 is expected to be less than 

5,000 acres (Pioneer 2009, table 20). If the DP-32138-1 is licensed to third parties and 

adopted across the entire U.S. seed industry, the total acreage is not expected to exceed

20,000 acres (Pioneer 2009, table 20).

FDA has completed review of the new protein consultations for DsRed2 and ZM-AA1 on 

January 29, 2010 and has no further questions.

Description of the Modification

 

2

Inbred lines are populations of identical or nearly identical plants used as stocks for the creation of hybrid

lines.

3 Male sterility - the inability to produce functional pollen.
3

DP-32138-1 corn was produced by transformation using disarmed Agrobacterium 

tumefaciens (Pioneer 2009, pp. 35 through 37, figures 11 and 12). Immature embryos of 

Hi-II (ms45/ms45) (Cigan 2001) were infected with Agrobacterium strain LBA4404 

containing plasmid PHP24597. Plants containing the introduced DNA were selected 

based on the production of a red color marker and then screened for male fertility

(Pioneer 2009, p. 35, figure 11). 

The plasmid PHP24597 contained three gene expression cassettes flanked by the right 

and left border of T-DNA from the Agrobacterium Ti-plasmid (Pioneer 2009, figure 13 & 

14, table 2):

Pollen fertility restorer Ms45 - expression cassette consists of two genetic elements

(Pioneer 2009, p. 43):

The 5126 anther-preferred4promoter from Z. mays localizes the expression to the 

anther (Cigan 1997).

The pollen fertility restoration gene (Ms45) from Z. mays restores development of 

the microspore cell wall that gives rise to pollen5(Cigan 2001). The presence of 

the transgene Ms45 allows for production of viable pollen.

α-Amylase zm-aa1 - expression cassette consists of four genetic elements (Pioneer 2009,

p. 43):

The polygalacturonase promoter (PG47) from Z. mays localizes expression to

pollen (Allen 1993).

Transit peptide brittle-1 (zm-bt1) from Z. mays targets expression to the 

amyloplast6(Sullivan 1991). The zm-aa1 gene was truncated to remove the native 

transit peptide sequence and replaced by the zm-bt1 amyloplast-targeting 

sequence.

The alpha-amylase (α-amylase)

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zm-aa1 gene from Z. mays (Pioneer 2009, figure 

43) encodes the ZM-AA1 protein which breaks down starch (Janeček 1994). 

When the ZM-AA1 protein is expressed in immature pollen, the depletion of 

starch reserves renders the pollen infertile. 

The In2-1 terminator from Z. mays from the In2-1 gene (Hershey 1991).

 

4

Pollen development takes place within the anther (Bedinger 1992). The 5126 promoter localizes 

expression to an inner cell layer of the anthers called the tapetum (petition figures 8A & 8B). 

5 Mutations in the Ms45 gene causes male sterility because there is no functional pollen produced. A 

mutation in the Ms45 gene is designated as ms45. 

6 Amyloplast is an organelle in the cytoplasm of plant cells where starch is stored.

7 Catalyze the hydrolysis of α-1,4- D-glucosidic bonds in polysaccharides such as starch.
4

Red color marker DsRed2(AltI) - expression cassette consists of four genetic elements

(Pioneer 2009, p. 43):

A 35S enhancer from the cauliflower mosaic virus (CaMV) (Odell 1985, Odell 

1988).

The lipid transfer protein (Ltp2) promoter from barley localizes expression to the 

aleurone layer of the seed (Kalla 1994).

The DsRed2 gene from a marine coral-like anemone Discosoma sp. (Matz 1999, 

Wasson-Blader 2001) was modified by a single base pair substitution (in which an 

internal BstEII restriction site was removed without changing the amino acid 

sequence in the DsRed2 protein) to produce DsRed2(AltI).

DP-32138-1 seeds expressing the DsRed2 protein are colored pinkish-red 

(Pioneer 2009, figure 10, Wasson-Blader 2001) and can be sorted from yellow 

seed (that does not express DsRed2) using a color sorting machine (Pioneer 2009,

figures 4, 5 and 10, Appendices 2 through 7). The DsRed2 protein enables

detection and sorting of transgenic red corn seeds from non-transgenic yellow 

seeds.

The proteinase inhibitor II (pinII) terminator from Solanum tuberosum (An 1989, 

Keil 1986).

Data from Southern blot analyses demonstrate that DP-32138-1 contains: (1) a single 

copy of the 5126 promoter and Ms45 gene (Pioneer 2009, table 4, figure 19); (2) a single 

copy of the PG47 promoter, zm-bt1 transit peptide, zm-aa1 gene and In2-1 terminator 

(petition table 4, figures 20 and 21); and (3) a single copy of the 35S enhancer, the Ltp2

promoter, DsRed2(AltI) and pinII terminator (Pioneer 2009, table 4, figures 22 and 23).

Potential of DP-32138-1 to Become Invasive and/or a Weed

Corn possesses few of the characteristics of those plants that are notably successful as 

weeds (Baker 1965, Keeler 1989). In the U.S., corn is not listed as a weed (Crockett 

1977, Holm 1979, Muenscher 1980), nor is it present in the Federal noxious weed list (7 

CFR part 360;8. Furthermore, corn is grown throughout the world without any report that 

it is a serious weed or that it forms persistent feral populations (Gould 1968). Like many 

domesticated crops, corn seed from a previous year’s crop can overwinter and germinate 

the following year. For instance, the appearance of corn seedlings in soybean fields 

following a corn crop is a common occurrence. Manual or chemical measures are often 

applied to remove these volunteers, but the plants that are not removed do not typically 

result in feral populations in following years. 

APHIS assessed whether DP-32138-1 is any more likely to become a weed than the

 

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isogenic nontransgenic corn line, or other corn varieties currently under cultivation. The 

assessment encompasses a thorough consideration of the basic biology of corn and an 

evaluation of the unique characteristics of DP-32138-1 under field conditions. Pioneer 

has been conducting agronomic field trials of DP-32138-1 since 2005 in the U.S. corn 

belt at over 43 locations (Pioneer 2009, Appendix 12). Agronomic data were collected 

from DP-32138-1 and its control counterparts in six locations that provide a range of 

environmental conditions representative of where the DP-32138-1 is expected to be 

grown for seed production (Pioneer 2009, figure 47). Field trial data (Pioneer 2009, pp. 

101- 107, tables 11 and 12) indicated that DP-32138-1 does not exhibit characteristics 

that would cause it to be weedier than the parental corn line. No differences in phenotypic 

characteristics that might contribute to enhanced weediness were observed between DP32138-1 and control lines for the wide range of phenotypic endpoints assessed in these 

field trials or in greenhouse or laboratory experiments (Pioneer 2009, table 11). There 

was no increase in weediness potential as measured by differences observed in the field 

for germination, seedling vigor, plant height, ear height, stalk lodging, root lodging, final 

population, plant health, time to silking, time to pollen, pollen viability, and seed 

germination (Pioneer 2009, tables 10 and 12). None of the measured attributes showed 

any differences relative to its comparator, suggesting that DP-32138-1 is not weedier than 

current corn cultivars. 

These results on growth characteristics, seed production and germination indicate that the 

DP-32138-1 is not significantly different from its comparators. There is no indication that 

DP-32138-1 possesses a selective advantage that would result in increased weediness. 

DP-32138-1 lacks the ability to persist as a troublesome weed, and there would be no 

significant impact on current weed management practices for corn cultivation.

Potential for Gene Flow and Gene Introgression from DP-32138-1 into SexuallyCompatible Relatives

Gene flow from crops to wild relatives may have the potential to enhance the weediness 

of wild relatives, as observed in rice, sorghum, sunflower, and a few other crops 

(Ellstrand 1999). Gene flow is a natural biological process with significant evolutionary 

importance. A number of angiosperm taxa are believed to be derived from hybridization 

or introgression between closely related taxa (Soltis 1993, Rieseberg 1997) and even in 

existing floras, the occurrence of hybridization or introgression is reported to be 

widespread (Stace 1987, Rieseberg 1993). It has been a common practice by plant 

breeders to artificially introgress traits from wild relativesinto crop plants to develop new 

cultivars.

APHIS evaluated the potential for gene introgression to occur from DP-32138-1 to 

sexually compatible wild relatives and considered whether such introgression would 

result in increased weediness. Cultivated corn is sexually compatible with other members 

of the genus Zea, and to a much lesser degree with members of the genus Tripsacum

(OECD 2003). The closest wild relatives of corn, various Zea species referred to as 

teosinte, are normally confined to the tropical and subtropical regions of Mexico, 
6

Guatemala, and Nicaragua. In the U.S. a fairly rare, sparsely dispersed feral population of 

teosinte has been reported in Florida (USDA Plant database9). 

The genus Tripsacum contains up to 16 recognized species, most of which are native to 

Mexico, Central and South America. Three of these species (T. dactyloides, T. 

floridatum, and T. lanceolatum) exist as wild and/or cultivated species in the continental 

U.S.; and two taxa (T. fasciculatum and T. latifolium) also occur in Puerto Rico (USDA 

PLANTS Database, accessed 11/9/2009). Though many of these species occur where 

corn might be cultivated, gene introgression from DP-32138-1 under natural conditions is 

highly unlikely. Hybrids of Tripsacum species with Zea are difficult to obtain outside of a 

laboratory and are often sterile or have greatly reduced fertility and none of them 

typically withstand even the mildest winters (Galinat 1988, Magelsdorf 1939). 

Furthermore, none of the sexually compatible relatives of corn in the U.S. are considered 

to be weeds in the U.S. (Holm 1979). Therefore, even in those instances of incidental 

gene flow between DP-32138-1 and wild relatives, the transgenes of DP-32138-1 are 

unlikely to transform corn wild relatives into more weedy species.

Introgression of genes from corn into teosinte or Tripsacum species has not been 

described to occur in nature in the U.S. While some teosinte may be considered weeds in 

certain instances, they are also used by some farmers for breeding improved maize 

(Sánchez 1997 and references therein). Teosinte is described as being susceptible to 

many of the same pests and diseases that attack cultivated corn (Sánchez 1997). In the 

wild, introgressive hybridization from corn to teosinte is currently limited, in part, by 

several factors including geographic isolation, differing degrees of genetic 

incompatibility, differences in flowering time in some cases, developmental morphology 

and timing of the reproductive structures, dissemination, and dormancy (Doebley 1990a 

and 1990b, Galinat 1988, Ellstrand 2007). First-generation hybrids are generally less fit 

for survival and dissemination in the wild and show substantially reduced reproductive 

capacity, which thus acts as a significant constraint to introgression. Even if gene flow to 

a wild relative of corn did occur, an engineered trait that does not offer any adaptive 

advantage will probably not persist in the weed population (Ellstrand 1990). DP-32138-1 

contains a male fertility gene that is normally present in corn, a male sterility gene, and a 

color selectable marker gene. None of these genes would be expected to confer a 

selective advantage if gene flow were to occur. Data included in the petition 

demonstrated that there were no significant differences in viability and morphology (as 

measured by size shape and color) of pollen collected from DP-32138-1 plants and nearisoline reference plants (Pioneer 2009, figure 9, table 12); therefore, the outcrossing rate 

of DP-32138-1 is not expected to be any different from other corn. Moreover, its 

potential impact due to the extremely limited potential for gene introgression into teosinte 

is not expected to be any different than that of other cultivated corn varieties. Therefore, 

USDA has determined that any adverse consequences of gene flow from DP-32138-1 to 

wild or weedy species in the U.S. are highly unlikely.

 

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Potential for Transfer of Genetic Information to Organisms with which DP32138-1 

Cannot Interbreed

APHIS assessed whether horizontal gene transfer might occur between DP-32138 corn 

and inserted genes with other organisms. However, such transfer and expression of DNA 

from a plant species to bacteria is unlikely to occur (Keese 2008). First, many bacteria (or 

parts thereof) that are closely associated with plants have been sequenced, including 

Agrobacterium and Rhizobium (Kaneko 2000, Kaneko 2002, Wood 2001). There is no 

evidence that these organisms contain genes derived from plants. Second, in cases where 

review of sequence data implied that horizontal gene transfer occurred, these events were 

inferred to have occurred on an evolutionary time scale on the order of millions of years 

(Brown 2003, Koonin 2001). Third, FDA has evaluated horizontal gene transfer 

following plant transformation with antibiotic resistance marker genes, and concluded 

that the likelihood of transfer of antibiotic resistance genes from plant genomes to 

microorganisms in the gastrointestinal tract of humans or animals, or in the environment, 

is remote (FDA 1998). Therefore, APHIS concludes that horizontal gene transfer is 

unlikely to occur and thus poses no significant environmental or plant pest risk.

Potential for DP32138-1 to have Altered Disease and Pest Susceptibilities 

APHIS assessed whether DP-32138-1 is likely to have significantly altered disease and 

pest susceptibility. This assessment encompassed a thorough consideration of the 

introduced trait and disease and pest susceptibility data from DP-32138-1 field trials. 

DP-32138-1 has been field tested in the U.S. since 2005 (Pioneer 2009, p. 101, Appendix 

12). Agronomic data was collected at six different locations in 2007 that provided a range 

of environmental conditions representative of where DP-32138-1 is expected to be grown 

(Pioneer 2009,figure 47). Pioneer routinely monitors their corn field trials for the 

following disease agents: Aspergillus sp., Aureobasidium zeae, Cercospora zeae-maydis,

Colletotrichum graminicola, Exserohilum turcicum, Fusarium spp., Gibberella zeae, 

Pantoea stewartii, Phytopthora spp., Puccinia polysora, Puccinia sorghi and Ustilago 

zeae (Pioneer 2009, Appendix 13, table 2). The corn insects monitored include 

Aphididae, Adoretus sinicus, Chaetocnema pulicaria, Chrysoperla carnea Cicadellidae, 

Coleoptera, Diabrotica spp., Glischrochilus quadrisignatus, Helicoverpa zea, 

Lepidoptera, Ostrinia nubilalis, Popillia japonica, Richia albicosta, Spodoptera 

frugiperda, Syrphidae, Tetranychidae, Thripidae (petition Appendix 13, table 1). The 

data submitted by Pioneer indicated no meaningful differences between DP-32138-1 and 

non-transgenic counterparts for disease or insect damage (Pioneer 2009, p. 107, 

Appendix 13, tables 1 and 2). 

Furthermore, DNA sequences derived from plant pests that were incorporated in DP32138-1 did not result in the production of infectious agents or disease symptoms in field 

trials with the plants, and so it is unlikely that DP-32138-1 could pose a plant pest risk. 

The description of the genetic modifications, including genetic elements, expression of 

the gene product and their functions for DP-32138-1 has been summarized above. 
8

The use of Agrobacterium for transforming DP-32138-1 is unlikely to propagate

infectious agents. Transformed plants used in the generation of DP-32138-1 were treated 

with an antibiotic to eliminate the Agrobacterium from plant culture using well known 

protocols (Pioneer 2009).

APHIS considered whether corn constituents that differed between DP-32138-1 corn and 

other corn varieties might be sufficient to lead to increased susceptibility to pathogens or 

pests. The data presented in the petition indicate no difference in compositional and 

nutritional quality of DP-32138-1 compared to conventional corn, apart from the 

presence of the MS45, ZM-AA1 and DsRed2 proteins (Pioneer 2009). None of the values 

for seed composition characteristics were outside the range of natural variability of 

conventional corn (Pioneer 2009, tables 13, 14, 15, 16, 17, 18 and 19). Therefore, the 

composition of DP-32138-1 is not biologically different than conventional corn (with the 

exception of the MS45, ZM-AA1 and DsRed2 proteins). Based on the known functions 

and mechanisms of actions of these proteins (summarized in Pioneer 2009), none of these 

proteins are expected to directly alter susceptibility to plant pathogens. Thus DP-32138-1

is expected to be susceptible to the same plant pathogens as conventional corn.

Corn is not a plant pest in the United States10, and the introduced DNA in DP-32138 is 

unlikely to pose a plant pest risk. Based on the analysis of genetic modifications and 

their functions and field testing data submitted by petitioner, APHIS concludes that there 

are no significant differences between DP-32138-1 corn and the non-transgenic 

counterparts relative to pest and disease susceptibility. 

Conclusion

APHIS has prepared this plant pest risk assessment in order to determine if event DP32138-1 is unlikely to pose a plant pest risk. Based on the information provided by the 

applicant and the lack of plant pest risk from the inserted genetic material, weedy 

characteristics, atypical responses to disease or plant pests in the field, effects on nontargets or beneficial organisms in the agro-ecosystem, and horizontal gene transfer, 

APHIS has concluded that event DP-32138-1 is unlikely to pose a plant pest risk. 

References

Allen RL, Lonsdale DM (1993) Molecular characterization of one of the maize 

polygalacturonase gene family members which are expressed during late pollen 

germination. Plant Journal 3:261-271.

An G, Mitra A, Choi HK, Costa MA, An K, Thornburg RW, Ryan CA (1989) Functional 

analysis of the 3’ control region of the potato wound-inducible proteinase inhibitor II 

gene. Plant Cell 1:115-122.

Bedinger P (1992) The remarkable biology of pollen. Plant Cell 4: 879-887.

 

10 http://www.aphis.usda.gov/plant_health/plant_pest_info/weeds/downloads/weedlist2006.pdf
9

Brewbaker JL (1964) Agricultural Genetics. Prentice-Hall, Englewood Cliffs, NJ.

Brown JR (2003) Ancient horizontal gene transfer. Nat. Rev. Genet. 4:121-132. 

Cigan AM, Unger E, Xu R-J, Kendall T, Fox T (2001) Phenotypic complementation of 

ms45 maize requires tapetal expression of MS45. Sex. Plant Reprod. 14:135-142.

Cigan AM, Albertsen MC (1997) Transgenic Plants and DNA Comprising Anther 

Specific Promoter 5126 and Gene to Achieve Male-Sterility. November 18, 1997. 

United States Patent No. 5,689,051.

Crockett L (1977) Wildly Successful Plants: North American Weeds. University of 

Hawaii Press, Hawaii.

Doebley J (1990a) Molecular evidence for gene flow among Zea species. BioScience 

40:443-448.

Doebley J (1990b) Molecular systematics of Zea (Gramineae). Maydica 35:143-50.

Ellstrand NC, Hoffman CA (1990) Hybridization as an avenue of escape for engineered 

genes. BioScience 40:438-442.

Ellstrand NC, Prentice HC, Hancock JF (1999) Gene flow and introgression from 

domesticated plants into their wild relatives. Annu. Rev. Ecol. Syst. 30:539-563.

Ellstrand NC, Garner L, Hegde S, Suadagnuolo R, Blancas L (2007) Spontaneous 

hybridization between maize and teosinte. Journal of Heredity 98:183-187.

FDA (1998) Guidance for Industry: Use of Antibiotic Resistance Marker Genes in 

Transgenic Plants. pp. 28.

Galinat WC (1988) The origin of corn. Pp. 1-31 In G. F. Sprague and J. W. Dudley, 

(eds.). Corn and corn improvement. American Society of Agronomy, Crop Science 

Society of America, and Soil Science Society of America, Madison, WI.

Gould FW (1968) Grass Systematics. McGraw-Hill, New York. 

Hershey HP, Stoner TD (1991) Isolation and characterization of cDNA clones for RNA 

species induced by substituted benzenesulfonamides in corn. Plant Molecular Biology 

17:679-690.

Holm L, Doll J, Holm E, Pancho JV, Herberger JP (1997) World Weeds: Natural 

Histories and Distribution. John Wiley and Sons, New York.

Janeček Š (1994) Sequence similarities and evolutionary relationships of microbial, plant 

and animal α-amylases. Eur. J. Biochem. 224:519-524.
10

Kalla R, Shimamoto K, Potter R, Nielsen PS, Linnestad C, Olsen OA (1994) The 

promoter of the barley aleurone-specific gene encoding a putative 7 kDa lipid transfer 

protein confers aleurone cell-specific expression in transgenic rice. Plant Journal 6(6): 

849-860

Kaneko T et al. (2000) Complete genome structure of the nitrogen-fixing symbiotic 

bacterium Mesorhizobium loti. DNA Research. 7:331-338.

Kaneko T et al. (2002) Complete genomic sequence of nitrogen-fixing symbiotic 

bacterium Bradyrhizobium japonicum USDA110. DNA Research 9:189-197

Keeler K (1989) Can genetically engineered crops become weeds? Bio/Technology 

7:1134-1139.

Keese P (2008) Risks from GMOs due to horizontal gene transfer. Environmental 

Biosafety Research 7:123-149.

Keil M, Sanches-Serrano J, Schell J, Willmitzer L (1986) Primary structure of a 

proteinase inhibitor II gene from potato. Nucleic Acids Research 14:5641-5650.

Koonin EV, Makarova KS, Aravind L (2001) Horizontal gene transfer in prokaryotes: 

quantification and classification. Annual Review of Microbiology. 55:709-742. 

Mangelsdorf PC, Reeves RG (1939) The Origin of Indian Corn and its Relatives. Texas 

Agricultural Experiment Station. Bulletin No. 574. 

Matz MV, Fradkov AF, Labas YA, Savitsky AP, Zaraisky AG, Markelov ML, Lukyanov 

SA (1999) Fluorescent proteins from non-bioluminescent Anthozoa species. Nature 

Biotechnology 17:969–973.

Muenscher WC (1980) Weeds. 2nd edition. Cornell University Press, Ithaca and

London.

Odell JT, Knowlton S, Lin W, Mauvais, CJ (1988) Properties of an isolated transcription 

stimulating sequence derived from the cauliflower mosaic virus 35S promoter. Plant 

Molecular Biology 10:263-273.

Odell JT, Nagy F, Chua, NH (1985) Identification of DNA sequences required for 

activity of the cauliflower mosaic virus 35S promoter. Nature 313:810-812.

OECD (2003) Consensus Document on the Biology of Zea mays subsp. mays (Maize). 

pp 1-49.

Pioneer (2009). Petition for the Determination of Nonregulated Status for Maize 32138 

SPT Maintainer Used in the Pioneer Seed Production Technology (SPT) Process. 
11

Submitted by N. Weber, Registration Manager. Pioneer Hi-Bred International, Inc., 

Johnston, IA (See Table: http://www.aphis.usda.gov/biotechnology/not_reg.html)

Rieseberg LH, Wendel JF (1993) Introgression and its Consequences in Plants. Pp. 70–

109 In RG Harrison (ed.) Hybrid Zones and the Evolutionary Process. Oxford 

University Press, Oxford. 

Rieseberg LH (1997) Hybrid origins of plant species. Annual Review of Ecology and 

Systematics 28:359-389.

Sánchez GJJ, Ruiz CJA (1997) Teosinte distribution in Mexico. Pp 18-39 In JA Serratos, 

MC Willcox, F Castillo-Gonzalez, (eds.) Gene flow among maize landraces, 

improved maize varieties, and teosinte: implications for transgenic maize. CIMMYT, 

Mexico, D.F.

Skibbe DS, Schnable PS (2005) Male sterility in maize. Maydica 50:367-367.

Sleper DA, Poehlman JM (2006) Breeding Corn (Maize). Chapter 17. Pp. 277-296 In

Breeding Field Crops, 5th Edition. Blackwell Publishing.

Soltis DE, Soltis PS (1993) Molecular data and the dynamic nature of polyploidy. 

Critical Reviews in Plant Sciences 12:243–273. 

Stace CA (1987) Hybridization and the plant species. Pp. 115–127 In KM Urbanska 

(ed.) Differentiation Patterns in Higher Plants. Academic Press, New York.

Sullivan TD, Strelow LI, Illingworth CA, Phillips RL, Nelson Jr OE (1991) Analysis of 

Maize Brittle-1 Alleles and a Defective Suppressor-Mutator-Induced Mutable Allele. 

Plant Cell 3:1337-1348.

USDA-APHIS (2009) Petitions of Nonregulated Status 

http://www.aphis.usda.gov/brs/not_reg.html Accessed January 11, 2010.

Wasson-Blader T (2001) Living ColorsTM DsRed2: Improved red fluorescent protein for 

use in living cells. Clontechniques 16:2-3

Wood DW, et al. (2001) The genome of the natural genetic engineer Agrobacterium 

tumefaciens C58. Science. 294:2317-2323.

Wych RD (1988) Production of hybrid seed corn. Pp 565-607 In GF Sprague (ed.). Corn 

and Corn Improvement, American Society of Agronomy, Inc., Crop Science Society 

of American Inc., and Soil Science Society of America, Inc. Madison, Wisconsin,.