Monsanto Petition (19-316-01p) for the Determination 

of Nonregulated Status for Dicamba, Glufosinate, 

Quizalofop and 2,4-Dichlorophenoxyacetic Acid 

Tolerant MON 87429 Maize with Tissue-Specific 

Glyphosate Tolerance Facilitating the Production of 

Hybrid Maize Seed

OECD Unique Identifier:

MON-87429-9 

Draft Plant Pest Risk Assessment

February 2, 2020 

Agency Contact:

Joseph Tangredi

Biotechnology Regulatory Services 

4700 River Road

USDA, APHIS

Riverdale, MD 20737

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on 

the basis of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or 

marital or family status. (Not all prohibited bases apply to all programs.) Persons with disabilities who 

require alternative means for communication of program information (Braille, large print, audiotape, etc.) 

should contact USDA’S TARGET Center at (202) 720–2600 (voice and TDD).

To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326–W, 

Whitten Building, 1400 Independence Avenue, SW, Washington, DC 20250–9410 or call (202) 720–5964 

(voice and TDD). USDA is an equal opportunity provider and employer.

Mention of companies or commercial products in this report does not imply recommendation or 

endorsement by the U.S. Department of Agriculture over others not mentioned. USDA neither guarantees 

nor warrants the standard of any product mentioned. Product names are mentioned solely to report 

factually on available data and to provide specific information.

This publication reports research involving pesticides. All uses of pesticides must be registered by 

appropriate State and/or Federal agencies before they can be recommended.
TABLE OF CONTENTS PAGE

A. Introduction ................................................................................................................. 3

b. Development of dicamba, glufosinate, quizalofop and 2,4-dichlorophenoxyacetic

acid resistant mon 87429 maize with tissue-specific glyphosate resistance

facilitating the production of hybrid maize seed ........................................................ 5

c. Description of inserted genetic material, its inheritance and expression, gene

products, and changes to plant metabolism................................................................ 8

d. Potential plant pest and disease impacts.................................................................... 15

e. Potential impacts on non-target organisms beneficial to agriculture......................... 19

f. Potential for enhanced weediness of mon 87429 maize............................................ 23

g. Potential impacts on the weediness of any other plants with which mon 87429 maize

can interbreed ........................................................................................................... 26

h. Potential changes to agriculture or cultivation practices........................................... 28

i. Potential impacts from transfer of genetic information to organisms with which mon

87429 maize cannot interbreed................................................................................. 30

j. Conclusion................................................................................................................. 33

k. References................................................................................................................. 34
3

A. Introduction

Monsanto Company (hereafter referred to as Monsanto) has petitioned the Animal and 

Plant Health Inspection Service (APHIS) of the United States of Department Agriculture 

(USDA) seeking a determination of nonregulated status for herbicide resistant1 maize 

(Zea mays) event MON 87429 (OECD Unique Identifier MON 87429-9, hereafter referred 

to as MON 87429 maize) developed using genetic engineering (modified maize) that is 

unlikely to pose a greater plant pest risk than the unmodified organism from which it was 

derived and, therefore, should no longer be a regulated organism under the APHIS’ 7 

Code of Federal Regulations (CFR) part 340. This petition was assigned the number 19- 

316-01p, and is hereafter referenced as Monsanto 2019. APHIS administers 7 CFR part 

340 under the authority of the plant pest provisions of the Plant Protection Act (PPA) of 

2000 (7 U.S.C. 7702 et seq.)2. This plant pest risk assessment was conducted to 

determine if MON 87429 maize is unlikely to pose a greater plant pest risk than the 

unmodified organism from which it was derived. 

The petition for non-regulated status described in this PPRA is being evaluated under the 

version of the regulations effective at the time that it was received. The Animal and Plant 

Health Inspection Service (APHIS) issued a final rule, published in the Federal Register 

on May 18, 2020 (85 FR 29790-29838, Docket No. APHIS-2018-0034)2, revising 7 CFR

part 340; however, the final rule is being implemented in phases. The new Regulatory 

Status Review (RSR) process, which replaces the petition for determination of 

nonregulated status process, became effective on April 5, 2021 for corn, soybean, cotton, 

potato, tomato, and alfalfa. The RSR process is effective for all crops as of October 1, 

2021. However, for corn petitions received prior to April 5, 2021 APHIS will review 

petitions for determination of non-regulated status in accordance with the legacy 

regulations at 7 CFR § 340.6. (85 FR 29815). This petition for a determination of nonregulated status is being evaluated in accordance with the regulations at 7 CFR § 340.6 

(2020) as it was received by APHIS on 6/27/2019. MON 87429 maize was produced by 

the Agrobacterium tumefaciens-mediated transformation method (Monsanto 2019), and 

three of the introduced genetic sequences come from plant pest organisms, including a 

promoter from the 35S RNA of cauliflower mosaic virus (CaMV) and the 25 base pairs of 

the right- and left-border T-DNA repeats from A. tumefaciens. Therefore, the MON 

87429 maize is considered a regulated organism under APHIS regulations at 7 CFR part

340. Monsanto has conducted introductions of MON 87429 maize as a regulated 

organism under APHIS-authorized permit/notification since 2014 (Appendix A, Table 

A-1 in Monsanto 2019), in part, to gather information to support that MON 87429 maize 

is unlikely to pose a greater plant pest risk than the unmodified organism from which it 

was derived.

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

risk associated with MON 87429 maize and its progeny and their use in the absence of

1 WSSA (1998) ""Herbicide Resistance" and "Herbicide Tolerance" defined. (Technology Note)." Weed 

Technology. 12 (4): p 789. Last Accessed: 02/21/2020. http://www.jstor.org/stable/3989101 2

 To view the final rule, go to www.regulations.gov and enter APHIS-2018-0034 in the Search Field.
4

confinement relative to the unmodified recipient and/or other appropriate comparators. 

APHIS utilizes data and information submitted by the applicant, in addition to current 

literature, to determine if MON 87429 maize is unlikely to pose a greater plant pest risk 

than the unmodified organism from which it was derived. APHIS regulations in 7 CFR 

340.6(c) specify the information needed for consideration in a petition for nonregulated 

status. APHIS will assess information submitted by the applicant about MON 87429 

maize related to: plant pest risk characteristics; expression of the gene product, new 

enzymes, or changes to plant metabolism; disease and pest susceptibilities and indirect 

plant pest effects on other agricultural products; effects of the regulated organism on nontarget organisms; weediness of the regulated organism; impact on the weediness of any 

other plant with which it can interbreed; changes to agricultural or cultivation practices 

that may impact diseases and pests of plants; and transfer of genetic information to 

organisms with which it cannot interbreed.

APHIS may also consider information relevant to reviews conducted by other agencies 

that are part of the ‘Coordinated Framework for the Regulation of Biotechnology’(51 FR

23302 1986; 57 FR 22984 1992). Under the Coordinated Framework, the oversight of 

biotechnology-derived plants rests with APHIS, the Food and Drug Administration 

(FDA), and the Office of Pesticide Programs of the U.S. Environmental Protection 

Agency (EPA). Depending on its characteristics, certain biotechnology-derived products 

are subjected to review by one or more of these agencies.

EPA regulates under the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) (7 

U.S.C. 136 et seq) the distribution, sale, use and testing of pesticidal substances produced 

in plants and microbes, including those pesticides that are produced by an organism 

through techniques of modern biotechnology. EPA also sets tolerance limits for residues 

of pesticides on and in food and animal feed, or establishes an exemption from the 

requirement for a tolerance, under the Federal Food, Drug, and Cosmetic Act (FFDCA) 

(21 U.S.C. Chapter 9). Prior to registration for a new use for a new or previously 

registered pesticide, EPA must determine through testing that the pesticide does not cause 

unreasonable adverse effects on humans, the environment, and non-target species when 

used in accordance with label instructions. EPA must also approve the language used on 

the pesticide label in accordance with 40 CFR part 158. Other applicable EPA regulations 

include 40 CFR part 152 - Pesticide Registration and Classification Procedures, part 174 -

Procedures and Requirements for Plant Incorporated Protectants (PIPs), and part 172 -

Experimental Use Permits. In support of Monsanto’s third generation herbicide resistant 

MON 87419 maize, deregulated by USDA in 2016, Monsanto requested that EPA allows 

the 0.5 lb a.e./ac postemergence application window for dicamba to be extended from V5 

to V8 growth stage or 36-inch height of maize, whichever occurs first, without reducing 

the application rate of dicamba (US-EPA 2019). Pending approval of the expanded label 

at EPA, the dicamba use pattern for MON 87429 would be no different than that of MON 

87419. Use of glufosinate, quizalofop and 2,4-D over the top of MON 87429 will follow 

the current labeled use patterns of these individual herbicides3,4,5. The introduction of

3 Federal Register, 77 FR 59106-59113, Glufosinate Ammonium, Pesticide Tolerances 4 Federal Register, 82 FR 9523-9529, 2,4-D; Pesticide Tolerances 5 Federal Register, 83 FR 7111-7115, Quizalofop ethyl; Pesticide Tolerances
5

MON 87429 stacked with a deregulated glyphosate resistance trait will follow the current 

labeled use patterns of glyphosate herbicide6

.

The FDA under the FFDCA is responsible for ensuring the safety and proper labeling of 

all plant-derived foods and feeds, including those developed through modern 

biotechnology. To help sponsors of foods and feeds derived from crops developed using 

genetic engineering comply with their obligations, the FDA encourages them to 

participate in its voluntary early food safety evaluation for new non-pesticidal proteins 

produced by new plant varieties intended to be used as food (US-FDA 2006) and a more 

comprehensive voluntary consultation process prior to commercial distribution of food 

or feed (57 FR 22984 1992). Monsanto has indicated that they are currently in 

consultation with the FDA following the policy, “Foods Derived from New Plant 

Varieties,” on the food and feed safety of MON 87429 maize (Submitted on February 5, 

2019).

B. Development of Dicamba, Glufosinate, Quizalofop and 2,4-

Dichlorophenoxyacetic Acid Resistant MON 87429 Maize with 

Tissue-Specific Glyphosate Resistance Facilitating the Production of 

Hybrid Maize Seed

Maize (Zea mays L. ssp mays) belongs to genus Zea, which consists of five species 

including Z. mays, Z. diploperennis, Z. luxurians, Z. nicaraguensis, and Z. perennis 

(OECD 2003; OTGR 2008). Maize is the only cultivated subspecies, and all the other 

subspecies and species in genus Zea are wild grasses and referred to as tesosintes (OTGR

2008). The closest known relative of genus Zea is genus Tripsacum. Maize can easily 

cross with the species of its own genus under natural conditions, but can only be crossed 

experimentally with the genus Tripsacum (OECD 2003).

Maize is widely grown in the world from 58° North (e.g., Canada and Russia) to 40° 

South (e.g., Chile) (Farnham et al. 2003; OTGR 2008), and it is the largest grain crop in 

the world in total metric ton production as of 2017 (FAOSTAT 2019). The top five maize 

production countries in 2016/2017 include USA (385 million metric tons (MMT)), China 

(264 MMT), Brazil (99 MMT), the European Union (62 MMT), and Argentina (41 

MMT) (USDA-FAS 2019). In the United States, maize is grown in almost all the states 

(Figure 1, colored areas) (USDA-NASS 2019a). As shown in Figure 2, there exists a 

significant year-to-year variability in planted acreages, ranging from 68 to 97 million 

acres in the past 20 years (USDA-NASS 2019b). Maize yields (bushels/acre) also differ 

from year to year but show an apparent increase over the years (Figure 3) (USDA-NASS

2019c-b).

Maize has been used as a basic food crop, but its primary use in industrialized countries 

shifts more towards animal feed in the form of grain, forage or silage (Farnham et al.

2003; OECD 2003). In developed countries, more than 85% of the maize is used to feed 

animals (Farnham et al. 2003). Maize can also be processed for a range of uses as

6 Federal Register, 76 FR 27268-27271, Glyphosate; Pesticide Tolerances
6

ingredients in food or drinks, or for industrial purposes, e.g., alcohol including fuel 

ethanol (OECD 2003; OTGR 2008).

Figure 1. Maize production areas in the U.S. (USDA-NASS 2019a)
7

Figure 2. Maize acreage by year in the U.S. (USDA-NASS 2019b)

Figure 3. Maize yield by year in the U.S. (USDA-NASS 2019c-b)
8

Monsanto by Agrobacterium mediated-transformation of immature embryos of the inbred 

maize line LH244 developed the herbicide resistant MON 87429 maize that is resistant to 

the herbicides dicamba, glufosinate, aryloxyphenoxypropionate (AOPP) acetyl coenzyme 

A carboxylase (ACCase) inhibitors (so called “FOPs” herbicides such as quizalofop) and 

2,4-dichlorophenoxyacetic acid (2,4-D). In addition, it provides tissue-specific glyphosate 

resistance to facilitate the production of hybrid maize seeds. The genetic engineering and 

breeding steps for the development of MON 87429 maize are described in the petition 

(Monsanto 2019).

The conventional control materials include the original transformation inbred line 

(LH244) and the F1 hybrid from the cross between LH244 and another conventional 

inbred line HCL617. LH244 was used as the control in molecular characterization 

studies. The F1 hybrid (LH244 × HCL617) was used as the control in compositional 

analysis studies and in phenotypic, agronomic and environmental interactions 

assessments. Where appropriate, commercial hybrid maize materials (reference hybrids) 

were also used to establish a range of variability or responses representative of 

commercial maize in the United States.

Based on maize biology (OECD 2003; OTGR 2008) and the data presented by Monsanto, 

APHIS concludes that MON 87429 maize was developed in a manner common to other 

modified maize and modified crops using Agrobacterium-mediated transformation 

(USDA-APHIS 2019a). APHIS believes the use of the non-GE control and other 

reference varieties as comparators is sufficient to determine that MON 87429 maize does 

not differ from the other maize varieties currently used in commercial production.

C. Description of Inserted Genetic Material, Its Inheritance and 

Expression, Gene Products, and Changes to Plant Metabolism

To inform the potential hazards resulting from the genetic modification and potential 

routes of exposure related to the inserted DNA and its expression products, APHIS 

assessed data and information presented in the petition related to: the transformation 

process; the source of the inserted genetic material and its function in both the donor 

organism and the modified crop event; and the integrity, stability and mode of 

inheritance of the inserted genetic material through sexual or asexual reproduction based 

on the location of the insertion (e.g., nucleus or organelle) and the number of loci 

inserted.

APHIS also assessed data presented in the petition on whether the genetic modification 

results in expression of new genes, proteins, or enzymes or changes in plant metabolism 

or composition in the MON 87429 maize relative to the conventional controls. The 

assessment encompasses a consideration of the expressed dicamba mono-oxygenase 

(DMO) protein, phosphinothricin-N-acetyltransferase (PAT) protein, FOPs and 2,4-D 

dioxygenase (FT_T) protein and 5-enolpyruvylshikimate-3-phosphate synthase from 

Agrobacterium sp. strain CP4 (CP4 EPSPS) as well as any observed or anticipated effects 

on plant metabolism including, e.g., any relevant changes in levels of metabolites,
9

antinutrients, or nutrients in harvested seed/forage etc. derived from MON 87429 maize 

compared to those in the conventional control and other comparators. 

This information is used later in this risk assessment to inform whether there is any 

potential for plant pest vectors or sequences to cause greater plant pest risks in the MON 

87429 maize; or for expression of inserted DNA, new proteins or enzymes, or changes in 

metabolism to affect plant pest or diseases, non-target beneficial organisms, weediness, 

agricultural practices that impact pest or diseases or their management, or plant pest risks 

through horizontal gene flow. 

Description of the genetic modification and inheritance of inserted DNA

MON 87429 maize was developed through Agrobacterium-mediated transformation of 

the immature embryo of maize inbred line LH244 using the disarmed PV-ZMHT519224 

binary vector (Monsanto 2019). The disarmed binary vector does not have the native TDNA region from tumor-inducing (Ti) plasmids normally responsible for the incitation of 

crown gall tumors upon A. tumefaciens infection (Gelvin 2003).

Binary Plasmid Vector PV-ZMHT519224

The disarmed PV-ZMHT519224 binary vector is approximately 17.8 kb. It contains four 

gene expression cassettes for the expression of four herbicide resistance genes, which are 

delineated by a right border (RB) and left border (LB) sequences of T-DNA as well as 

backbone vector sequences outside of the two T-DNA border sequences. Transgene 

elements within the T-DNA regions are shown in Figure 4 and Table 1 below (Monsanto 

2019).

Figure 4. Schematic Representation of transgene elements within the T-DNA regions in 

MON 87429 maize (Figure IV-3, Monsanto 2019). 

Table 1. The genetic elements and functions of the tandemly arrayed four gene 

expression cassettes in MON 87429 maize for the expression of genes pat, dmo, ft_t, and 

cp4 epsps. 

Genetic Element Function

B-Left Border Region DNA region from A. tumefaciens containing the left border 

sequence used for transfer of the T–DNA
10

P2-Ea.Ubq Promoter, 5' UTR, and intron sequences for a ubiquitin gene (Ubq) 

from Erianthusravennae (plume grass) that directstranscription in

plant cells

CS-pat Coding sequence for the PAT protein of Streptomyces 

viridochromogenesthat confersresistance to glufosinate

T-Fba 3' UTR sequence of the fructose-bisphosphate aldolase (Fba) gene 

from Setaria italica (foxtail millet) that directs polyadenylation of

mRNA

P-Clj.Ubq Promoter, 5' UTR, and intron sequencesfor a ubiquitin gene (Ubq)

from Coix lacryma-jobi (adlay millet) that directs transcription in 

plant cells

TS-APG6 Codon optimized targeting sequence of the Albino and pale green 

6 (Apg6) gene from Arabidopsis thaliana encoding a chloroplasttargeted Hsp101 homologue transit peptide region that directs the

protein to the chloroplast

CS-dmo Codon optimized coding sequence for the dicamba mono–

oxygenase (DMO) protein of Stenotrophomonas maltophilia that 

confers dicamba resistance

T-Mt 3' UTR sequence of the OsMt gene from O. sativa encoding 

metallothionein-like protein that directs polyadenylation of mRNA

P-Ad.Ubq Promoter, 5' UTR, and intron sequencesfor a ubiquitin gene (Ubq)

from Arundo donax (giant reed) that directs transcription in plant 

cells

TS-MDH Targeting sequence from A. thaliana Mdh gene encoding the

malate dehydrogenase transit peptide region that directs the protein 

to the chloroplast

CS-ft_t Coding sequence of modified version of R-2,4-

dichlorophenoxypropionate dioxygenase (Rdpa) gene from 

Sphingobium herbicidovorans that expresses a FOPs and 2,4-D 

dioxygenase protein (FT_T) that conferstolerance to quizalofop

and 2,4-D herbicides

T-Nam 3' UTR sequence from the gene coding for a no apical meristem 

(Nam) protein domain containing protein from O. sativa

P-35S Promoter and leader from the 35S RNA of cauliflower mosaic 

virus (CaMV) that directs transcription in plant cells

L6-Cab 5' UTR leader sequence from the gene coding for chlorophyll a/bbinding (CAB) protein of Triticum aestivum (wheat) that is 

involved in regulating gene expression

I7-Ract1 Intron and flanking UTR sequence of the act1 gene from O.sativa

encoding rice Actin 1 protein that is involved in regulating gene 

expression.

TS-CTP2 Targeting sequence of the ShkG gene from A. thaliana encoding

the EPSPS transit peptide region that directs transport of the 

protein to the chloroplast

CS-cp4 epsps Codon optimized coding sequence of the 5-enolpyruvylshikimate3-phosphate synthetase (aroA) gene from the Agrobacterium sp. 

strain CP4 encoding the CP4 EPSPS protein that provides 

glyphosate tolerance

siRNA Target Sequence Modified partial 3' UTR sequence of Zea mays cDNA that 

contains male tissue specific siRNA target sequence

T-Grp3 3' UTR sequence of the glycine-rich RNA binding- protein (Grp3)

gene from O. sativa encoding the GRP3 protein that directs 

polyadenylation of mRNA
11

B-Right Border Region DNA region from A. tumefaciens containing the right border

sequence used for transfer of the T–DNA

T-DNA in transformation vector PV-ZMHT519224 contains the following four gene 

expression cassettes.

• The pat gene expression cassette contains a ubiquitin gene (Ubq) promoter from 

Erianthus ravennae (plume grass), the phosphinothricin-N-acetyltransferase gene 

(pat) from Streptomyces viridochromogenes that expresses the PAT protein to 

confer resistance to glufosinate herbicide, and a 3' UTR sequence of the fructosebisphosphate aldolase (Fba) gene from Setaria italica (foxtail millet).

• The dmo gene expression cassette contains a ubiquitin gene (Ubq) promoter from 

Coix lacryma-jobi (adlay millet), a targeting sequence of the Albino and pale 

green 6 (Apg6) gene from Arabidopsis thaliana encoding a chloroplast-targeted 

Hsp101 homologue transit peptide region that directs the protein to the 

chloroplast, a demethylase gene (dmo) from Stenotrophomonas maltophilia that 

expresses a dicamba mono-oxygenase (DMO) protein to confer tolerance to 

dicamba herbicide, and a 3' UTR sequence of the OsMt gene from O. sativa 

encoding metallothionein-like protein. 

• The ft_t gene expression cassette contains a ubiquitin gene (Ubq) promoter from 

Arundo donax (giant reed), a, targeting sequence from A. thaliana Mdh gene 

encoding the malate dehydrogenase transit peptide region that directs the protein 

to the chloroplast, a R-2,4-dichlorophenoxypropionate dioxygenase (Rdpa) gene 

from Sphingobium herbicidovorans that expresses a FOPs and 2,4-D dioxygenase 

protein (FT_T) that confers tolerance to quizalofop and 2,4-D herbicides, and a 3' 

UTR sequence from the gene coding for a no apical meristem (Nam) protein 

domain containing protein from O. sativa. 

• The cp4 epsps gene expression cassette contains the promoter and leader from the 

35S RNA of cauliflower mosaic virus (CaMV), an intron and flanking UTR 

sequence of the act1 gene from O. sativa (rice) encoding rice Actin 1 protein, the 

5-enolpyruvylshikimate-3-phosphate synthetase gene from the Agrobacterium sp. 

strain CP4 (cp4 epsps) encoding the CP4 EPSPS protein that provides glyphosate 

resistance, the modified partial 3' UTR sequence of Zea mays cDNA that contains 

male tissue specific siRNA target sequence, and the 3' UTR sequence of the 

glycine-rich RNA binding- protein (Grp3) gene from O. sativa. Tissue-specific 

expression of CP4 EPSPS protein in MON 87429, allowing for glyphosate 

induced non-viable pollen phenotype, is the second generation of Monsanto’s 

Roundup® Hybridization System (RHS) for hybrid seed production. 

Among the above transgene elements inserted into MON 87429 maize, three elements, 

including the T-DNA right- and left-border sequences from A. tumefaciens and a
12

promoter from the 35S RNA of cauliflower mosaic virus (CaMV) are associated with 

plant pests that are listed in 7 CFR 340.2. However, none of them is known to cause 

plant diseases.

Characteristics, Stability, and Inheritance of the Introduced DNA

Monsanto has provided data to characterize the inserted DNAs in MON 87429 maize 

with a combination of techniques including sequencing, PCR and bioinformatics 

(Monsanto 2019). The data demonstrate that MON 87429 maize contains a single copy of 

the T-DNA inserted into a single locus but does not contain DNA fragments from the 

vector backbone of plasmid PV-ZMHT519224. 

A sequence comparison between the sequence generated from the 5' and 3' flanking 

sequences of MON 87429 and the sequence from the conventional control indicates that 

54 bases of maize genomic DNA were deleted during integration of the T-DNA. There 

also was a 29-base insertion in the MON 87429 5′ flanking sequence and a 31 base 

insertion in the MON 87429 3' flanking sequence (Monsanto, 2019). Such changes are 

common during plant transformation (Anderson et al. 2016).

To assess the inheritance and stability of the MON 87429 T-DNA, phenotypic and 

genotypic segregation data were recorded during development of MON 87429 and 

analyzed using Chi square (χ2) analysis over several generations. The χ2 analysis results 

indicate that the MON 87429 T-DNA resides at a single locus within the maize genome 

and is stably inherited according to Mendelian principles. 

Next Generation Sequencing (NGS) reads from five breeding generations of MON 87429 

demonstrate the genetic stability of the T-DNA present in MON 87429 through multiple 

breeding generations. This comprehensive NGS and bioinformatic analysis of NGS data 

from multiple generations also supports the conclusion that MON 87429 contains a 

single, stable, inserted T-DNA.

Monsanto (2019) also demonstrates that MON 87429 maize showed the expected 

reduction of CP4 EPSPS protein expression in pollen with no impact on endogenous 

plant gene expression through using an endogenous maize regulatory element to target 

CP4 EPSPS mRNA for degradation in tassel tissues.

In summary, these results demonstrate that MON 87429 contains a single copy of the 

intended T-DNA containing the pat, dmo, ft_t, and cp4 epsps expression cassettes that is 

stably integrated at a single locus with no plasmid backbone sequences and is inherited 

according to Mendelian principles over multiple generations.

Expression of inserted DNA, changes in gene expression, new proteins or metabolism

As described above, MON 87429 maize contains dmo, pat, cp4 epsps and ft_t expression 

cassettes for the expression of the DMO, PAT, CP4 EPSPS and FT_T proteins, 

respectively (Figure 4). DMO, PAT, CP4 EPSPS and FT_T protein levels in forage, root,
13

leaf and grain of MON 87429 were determined using a multiplexed immunoassay. To 

further demonstrate the MON 87429 RHS trait mode-of-action (MOA), CP4 EPSPS 

expression in pollen tissue was determined to illustrate the differential expression 

between vegetative and pollen tissue.

DMO Protein

The dmo expression cassette expresses two forms of mature DMO protein with only one 

amino acid (cysteine) difference at the N-terminus due to alternative processing of the 

chloroplast transit peptide (CTP). One form consists of 341 amino acids while the other 

form of the DMO protein consists of 340 amino acids. The expression of the DMO 

protein confers resistance to dicamba herbicide. The mean DMO protein level in MON 

87429 across all sites was highest in leaf at 35 μg/g dw and lowest in root at 2.3 μg/g dw. 

The mean DMO protein level in MON 87429 grain was 2.4 μg/g dw (Monsanto, 2019).

PAT Protein

Expression of the pat gene in MON 87429 results in a single polypeptide of 182 amino 

acids that are identical to the wild type PAT protein encoded by S. viridochromogenes 

and to the PAT proteins produced in several commercially available glufosinate resistant 

crops except for the first methionine that is removed due to co-translational processing in 

MON 87429 (Monsanto 2019). PAT protein levels were determined in forage, leaf, root 

and grain tissues. The mean PAT protein level in MON 87429 across all sites was highest 

in leaf at 5.8 μg/g dw and lowest in grain at 0.84 μg/g dw.

CP4 EPSPS Protein

MON 87429 contains a 5-enolpyruvulshikimate-3-phosphate synthase (EPSPS) gene 

from Agrobacterium sp. strain CP4 (cp4 epsps) that expresses an EPSPS protein with a 

single polypeptide chain of 455 amino acids (CP4 EPSPS). The mean CP4 EPSPS protein 

level in MON 87429 across all sites was the highest in leaf at 54 μg/g dw and lowest in 

grain at 0.63 μg/g dw. As intended the mean CP4 EPSPS protein level in MON 87429 

pollen across all sites was below the limit of quantitation (0.11 μg/g dw).

FT_T Protein

The ft_t gene in MON 87429 is a modified version of the R-2,4-

dichlorophenoxypropionate dioxygenase (Rdpa) gene from the soil bacteria Sphingobium

herbicidovorans. The mean FT_T protein level in MON 87429 across all sites was the 

highest in leaf at 440 μg/g dw and lowest in root at 41 μg/g dw. The mean FT_T protein 

level in MON 87429 grain was 47 μg/g dw.

Potential new ORFs

Directed sequencing (locus-specific PCR, DNA sequencing and analyses) performed on 

MON 87429 was used to determine the complete sequence of the single DNA insert from
14

PV-ZMHT519224, the adjacent flanking genomic DNA, and the 5' and 3' insert-to-flank 

junctions. This analysis demonstrated that the sequence and organization of the DNA is 

identical to the corresponding region in the PV-ZMHT519224 T-DNA. Furthermore, the 

analysis of the genomic organization at the insertion site in MON 87429 showed that 54 

bases were deleted upon T-DNA integration. There also was a 29 base insertion in the 

MON 87429 5′ flanking sequence and a 31 base insertion in the MON 87429 3′ flanking 

sequence. Such changes are common during plant transformation (Anderson et al. 2016) 

and these changes presumably resulted from DNA repair mechanisms in the plant during 

Agrobacterium-mediated transformation processes (Salomon and H. 1998). No major 

DNA rearrangement occurred at the insertion site in MON 87429 upon DNA integration 

and the flanking sequences are not functional elements (Monsanto 2019).

Metabolism composition Analysis

To assess any potential metabolite alteration as a result of the expression of the above 

inserted genes, Monsanto analyzed the metabolism composition of MON 87429 maize 

grain and forage samples collected from five field sites that were representative of U.S. 

maize growing regions (Monsanto 2019). The production of materials for compositional 

analyses used a sufficient variety of field trial sites, reflecting a range of environmental 

conditions under which MON 87429 is expected to be grown and robust field designs 

(randomized complete block design with four replicates). MON 87429 plots were treated 

with dicamba, glufosinate, quizalofop and 2,4-D to generate samples under conditions of 

the intended use of the product. Samples were subjected to sensitive analytical methods 

that allow quantitative and accurate measurements of key components.

For MON 87429 maize, the introduced proteins, DMO, PAT, CP4 EPSPS and FT_T, 

confer herbicide resistance and lack catalytic activity that is intended to or expected to 

affect the plant’s metabolism. Given the nature of these introduced traits and the overall 

lack of meaningful unintended compositional characteristics observed for biotechnologyderived products characterized to date (Herman and Price 2013; Venkatesh et al. 2015), 

compositional changes that would affect the levels of components in MON 87429 maize 

were not expected.

Composition data for 25 metabolic components including major nutrients in grain 

(protein, amino acids, total fat, linoleic acid, carbohydrates, acid detergent fiber, neutral 

detergent fiber and ash), major nutrients in forage (protein, total fat, carbohydrates, acid 

detergent fiber, neutral detergent fiber and ash) and anti-nutrients in grain (phytic acid 

and raffinose) were analyzed. The statistical comparison of MON 87429 maize and the 

conventional control was based on compositional data combined across all five field 

sites. It is noteworthy that a statistically significant difference between MON 87429 and 

the conventional control does not necessarily imply biological relevance from a food and 

feed safety perspective. A mean difference less than the variability seen due to natural 

environmental variation within the single, closely related germplasm is typically not a 

food or feed safety concern (Venkatesh et al. 2015). Only if the impact of MON 87429 on 

levels of metabolic components is large relative to natural variation inherent to 

conventional maize would the difference in composition be potentially meaningful from a 

food and feed safety and nutritional perspective. Therefore, the difference between MON
15

87429 and the conventional control was evaluated in the context of variation within the 

conventional control germplasm grown across multiple sites (i.e., variation due to 

environmental influence) by determining the range of replicate values for the 

conventional control.

There were no statistically significant differences for 23 of the 25 metabolic components 

analyzed from MON 87429 grain and forage (Table VI-1–Table VI-4 in Monsanto 2019). 

Two components (total fat and linoleic acid in grain) showed a statistically significant 

difference between MON 87429 and the conventional control (Table VI-1 in Monsanto 

2019). For total fat, the mean values for MON 87429 maize and the conventional control 

were 3.76 % dw and 3.88 % dw, respectively with a difference of -0.15 % dw. For 

linoleic acid, the mean values for MON 87429 and the conventional control were 55.53

% Total Fatty Acid (FA) and 55.21 % Total FA, respectively, with a difference of 0.32 % 

Total FA. For these components, however, the difference between MON 87429 and the 

conventional control was less than the conventional control range values. Furthermore, 

the MON 87429 mean component values were within the range of values observed in the 

literature and/or the ILSI-CCDB values (Table VI-5 in Monsanto 2019). Thus, these data 

indicated that the statistically significant differences observed in total fat and linoleic acid 

in grain did not imply biological relevance from a food and feed safety perspective.

In summary, the expression of the inserted DNAs and the resulting phenotype in MON 

87429 maize are consistent with the inheritance of the introduced genetic material. The 

sequence analysis showed no evidence supporting any potential creation of new ORFs or 

any unintended effects resulting from the insertion of the genetic materials (Monsanto 

2019). The compositional analyses demonstrated that introduction of the PVZMHT519224 T-DNA in MON 87429 maize achieved the intended expression of DMO, 

PAT, CP4 EPSPS and FT_T for herbicide resistance while maintaining the equivalent 

metabolism composition of gain and forage tissues in comparison to the control and other 

conventional maize varieties.

D. Potential Plant Pest and Disease Impacts

APHIS assessed whether potential plant pest or disease impacts are likely to result from 

the transformation process, from DNA sequences of plant pests, or from any other 

expression products, new enzymes, proteins or changes in plant metabolism or 

composition in MON 87429 maize that are known or anticipated to cause disease 

symptoms, or to affect plant pests or diseases or plant defense responses. APHIS also 

assessed whether MON 87429 maize is likely to have significantly increased disease and 

pest susceptibility based on data and observations from field trials on specific pest and 

disease damage or incidence and any agronomic data that might relate to such damage. 

Impacts or changes are assessed to determine if they would (1) affect the modified crop 

and/or result in significant introduction or spread of a damaging pest or disease to other 

plants; (2) result in the introduction, spread, and/or creation of a new disease; and/or (3) 

result in a significant exacerbation of a pest or disease for which APHIS has a control 

program. Any increase in pest or disease susceptibility is evaluated with respect to the
16

context of currently cultivated varieties, the ability to manage the pest or disease, and the 

potential impact on agriculture.

Plant Protection and Quarantine (PPQ) is an APHIS program that safeguards agriculture 

and natural resources from the entry, establishment, and spread of animal and plant pests 

and noxious weeds into the United States of America; and supports trade and exports of

U.S. agricultural products. PPQ responds to many new introductions of plant pests to 

eradicate, suppress, or contain them through various programs in cooperation with state 

departments of agriculture and other government agencies. These may be emergency or 

longer term domestic programs that target a specific pest. A variety of insect, plant 

disease, mollusk, nematode or weed programs exist including the programs for 

grasshoppers (Order Orthoptera) on rangelands, light brown apple moth (Epiphyas 

postvittana) in California, and of more relevance, Japanese beetle (Popillia japonica), 

Old World bollworm (Helicoverpa armigera), and witchweed (Striga asiatica) that can 

affect maize (USDA-APHIS 2019b).

The grasshoppers are normally natural components of the rangeland ecosystem (Figure 

5), but they can invade adjacent cropland and cause serious economic losses when their 

populations reach outbreak levels, especially when accompanied by a drought condition.

Figure 5. 2019 U.S. rangeland grasshopper hazard
17

The light brown apple moth (LBAM) can damage a wide range of crops and other plants. 

The LBAM was found in California in 2007, and some areas have been designated as 

quarantined areas (Figure 6).

Figure 6. 2018 Quarantined areas for light brown apple moth in California

The Japanese beetle is a highly destructive plant pest that can be very difficult and 

expensive to control. Japanese beetle adults attack the foliage, flowers, or fruits of more 

than 300 different ornamental and agricultural plants. Japanese beetles have spread 

throughout many states of the U.S. (Figure 7). APHIS maintains the Japanese Beetle 

Quarantine and Regulations that can be found in 7 CFR 301.48 with the objective to 

protect the agriculture of the Western United States and prevent the human-assisted 

spread of the beetle from the Eastern U.S.
18

The Old-World bollworm can affect 180 species of plants, with maize listed as one of its 

preferred hosts. It is closely related to the corn earworm (Helicoverpa zeae). Old World 

bollworm was first detected in western Puerto Rico in September 2014, and APHIS is 

conducting a variety of activities to protect the continental U.S from this pest (USDAAPHIS 2019b).

Witchweed (Striga asiatica) is a parasitic plant listed as a Federal Noxious Weed that 

affects maize and several other crops. Infested areas are found in North and South 

Carolina, and APHIS and state collaborators aim to stop the spread from infested areas 

and eradicate the pest (USDA-NRCS 2019j).

Maize itself is not considered a plant pest in the United States (7 CFR 340.2). The 

Agrobacterium strain A. tumefaciens used in the generation of MON 87429 maize was 

disarmed and also was already removed with antibiotics during the transformation 

process. The inserted DNA elements derived from plant pests do not result in the 

production of infectious agents or disease symptoms in plants. The genetic modifications 

of MON 87429 maize including genetic elements, expression of the gene products and 

their functions have been summarized above and are not expected to impart any new 

plant pest or disease risk than comparator maize lines.

Monsanto evaluated the differences between MON 87429 maize and conventional control 

plants of the damages from the 14 assessed arthropods (aphids, armyworms, billbugs, 

corn earworms, corn flea beetles, corn rootworm beetles, cutworms, European corn 

borers, grasshoppers, Japanese beetles, sap beetles, slugs, spider mites, and stink bugs)
19

and 10 assessed diseases (anthracnose, corn stunt, eyespot, Goss's bacterial wilt, gray leaf 

spot, leaf blight, northern leaf spot, rust, smut (head and ear), and Stewart's wilt) 

(Monsanto 2019). The differences of MON 87429 maize, conventional control, and 

commercial references in their responses to arthropod pests and diseases were evaluated 

at natural levels (no artificial infestation) during the growing season at the following 

growth stages: V5 – V8, V12 – R1, R1 – R3, and R4 – R5 at each of eight field sites. No 

differences were observed between MON 87429 and the conventional control for both 

arthropod and disease damages.

These data demonstrate that the integration of the T-DNA of plasmid PV-ZMHT519224 

and the expression of DMO, PAT, CP4 EPSPS and FT_T for herbicide resistance in MON 

87429 maize did not significantly alter the insect predation and disease occurrence or 

render MON 87429 maize more susceptible to pests and diseases over its control or 

reference maize varieties. Also, as discussed earlier, there were no observed or 

anticipated unintended metabolic composition changes in MON 87429 maize that could 

impart any new plant pest or disease risk compared to conventional maize (Monsanto 

2019). Thus, MON 87429 maize is unlikely to be more susceptible to plant pathogens and 

insect pests than conventional maize. For this reason, MON 87429 maize is unlikely to 

differ from conventional maize in its ability to harbor or transmit plant pathogens or pests 

and cause indirect plant pest effects on other agricultural products.

E. PotentialImpacts on Non-target Organisms Beneficial to Agriculture

The MON 87429 maize is not engineered for pest resistance other than for the expression 

of DMO, PAT, CP4 EPSPS and FT_T for herbicide resistance. Thus, Mon 87429 maize 

does not possess pesticidal activity, nor has ‘target’ species. APHIS assessed whether 

exposure or consumption of the MON 87429 maize would have a direct or indirect 

adverse impact on species beneficial to agriculture. Organisms considered were 

representatives of the species associated with production of the regulated crop in the 

agricultural environment. The assessment includes an analysis of data and information on 

MON 87429 maize compared to the conventional maize counterpart for any biologically 

relevant changes in the phenotype or substances (e.g., proteins, nutrients, or antinutrients) produced which may be novel or expressed at significantly altered amounts that 

are associated with impacts on organisms beneficial to agriculture, and/or any 

observations of beneficial organisms associated with the plants.

As described above in Section C, the inserted T-DNA in MON 87429 maize encodes four 

proteins novel to maize, DMO, PAT, CP4 EPSPS and FT_T that confer herbicide 

resistance. These proteins have been assessed in multiple products by USDA-APHIS and

U.S. FDA in the past years. The modes-of-action and experimental evidence reviewed in 

the current and/or previously submitted Petitions supports that these four proteins are 

safe; and no safety concerns have occurred during the history of environmental exposure 

to DMO, PAT, CP4 EPSPS and the alpha-ketoglutarate-dependent dioxygenase family of 

proteins to which FT_T belongs.
20

DMO Protein

MON 87429 maize contains a demethylase gene (dmo) from Stenotrophomonas 

maltophilia that expresses a dicamba mono-oxygenase (DMO) protein. The DMO protein 

enzymatically catalyzes the demethylation of the broadleaf herbicide dicamba to the nonherbicidal compound 3,6-dichlorosalicylic acid (DCSA) and formaldehyde, thus 

conferring dicamba resistance (Chakraborty et al. 2005). DMO protein is part of a large 

oxygenase family of enzymes that incorporate one or two oxygen atoms into substrates 

and are widely distributed in many universal metabolic pathways (Harayama et al. 1992). 

The DCSA product of the reaction catalyzed by the DMO protein is a known metabolite 

of dicamba in conventional cotton, soybean, soil, and livestock, and its safety has been 

evaluated by the FAO-WHO (FAO-WHO 2010).

The DMO protein in MON 87429 maize possesses a high level of sequence identity and 

structural and functional similarity with DMO proteins expressed in modified crops that 

were deregulated by USDA-APHIS (USDA-APHIS 2019a). Furthermore, these modified 

crops expressing DMO proteins completed consultation with U.S. FDA, where it was 

demonstrated that food and feed derived from these events are not materially different 

than the respective conventional crops. Thus, prior safety assessments of the DMO 

protein expressed in other modified crops demonstrating the lack of impact on plant pest 

potential, the lack of homology to known protein toxins or allergens, digestibility in in 

vitro digestion assays and lack of acute oral toxicity are directly applicable to the DMO 

protein expressed in MON 87429 maize.

PAT Protein

The phosphinothricin N-acetyltransferase (PAT) acetylates herbicide glufosinate in the 

presence of acetyl CoA to form non-herbicidal N-acetyl glufosinate, thus conferring 

glufosinate resistance to the crop. The PAT proteins have been isolated from two separate 

species of Streptomyces, S. hygroscopicus (Thompson et al. 1987) and S. 

viridochromogenes (Wohllehen et al. 1988). The PAT protein isolated from S. 

hygroscopicus is encoded by the bar gene, and the PAT protein isolated from S. 

viridochromogenes is encoded by the pat gene. MON 87429 maize contains the pat gene 

from S. viridochromogenes. These two PAT proteins are made up of 183 amino acids 

with 85% identity to each other at the amino acid level (Wohllehen et al. 1988), and are 

considered to be equivalent with regard to function and safety (OECD 1999).

The PAT proteins have a robust history of safe consumption and safe use in agriculture 

that is supported by the lack of any documented reports of adverse human or animal 

affects since the introduction of modified crops expressing PAT proteins in 1995 (Duke

2005). Numerous glufosinate-resistant crops including maize, canola, soybean, sugar 

beet, rice and cotton have been deregulated by USDA-APHIS (USDA-APHIS 2019a), 

where it was demonstrated that food and feed derived from these crops are not materially 

different than the respective conventional crops. The safety of PAT proteins has been 

confirmed following extensive reviews by regulatory agencies in many other countries 

for more than 30 modified crop events in several different crop species (e.g., maize,
21

soybean, cotton, canola and sugar beet). Furthermore, the EPA has issued a tolerance 

exemption for PAT protein (US-EPA 1999). Given that the PAT protein expressed in 

MON 87429 is almost identical to PAT proteins produced in other commercially 

available glufosinate resistant crops, prior safety assessments of the PAT proteins 

expressed in these other modified crops demonstrating lack of impact on plant pest 

potential, lack of homology to known protein toxins or allergens, digestibility in in vitro 

digestion assays and lack of acute oral toxicity are directly applicable to the PAT protein 

expressed in MON 87429 maize.

CP4 EPSPS Protein

5-enolpyruvulshikimate-3-phosphate synthase (EPSPS) is a key enzyme involved in 

aromatic amino acid biosynthesis and it catalyzes an enzymatic reaction to form 5-

enolpyruvylshikimate-3-phosphate (EPSP) and inorganic phosphate, leading to the 

biosynthesis of aromatic amino acids (phenylalanine, tryptophan and tyrosine) and other 

aromatic molecules that are necessary for plant growth (Alibhai and Stallings 2001).

Glyphosate inhibits the endogenous plant EPSPS enzyme, thereby depriving plants of 

essential amino acids (Steinrucken and Amrhein 1980).

MON 87429 contains an EPSPS gene from Agrobacterium sp. strain CP4 (cp4 epsps) that 

expresses the CP4 EPSPS protein. Although the CP4 EPSPS protein expressed in MON 

87429 is structurally similar and functionally identical to endogenous plant EPSPS 

enzymes, it has a much-reduced affinity for glyphosate and thus confers resistance to 

glyphosate (Sikorski and Gruys 1997). Additionally, MON 87429 maize utilizes an 

endogenous maize regulatory element to target CP4 EPSPS mRNA for degradation 

specifically in tassel tissues, resulting in reduced CP4 EPSPS protein expression in 

pollen. Appropriately timed glyphosate applications result in a sterile pollen phenotype 

and thus, allow for desirable cross pollinations to be made in maize without using 

traditional methods to control self-pollination in female inbred parents.

The safety and mode-of-action of CP4 EPSPS protein is studied extensively and well 

documented (ILSI 2010). The CP4 EPSPS protein has a robust history of safe 

consumption and safe use in agriculture as supported by the lack of any documented 

reports of adverse human or animal effects since the introduction of modified crops 

expressing CP4 EPSPS protein. Numerous glyphosate-resistant, commercially available 

CP4 EPSPS containing crops have been deregulated by USDA-APHIS (USDA-APHIS

2019a) and have completed consultations with the FDA, where it was demonstrated that 

food and feed derived from these crops are not materially different than the respective 

conventional crops. The safety of the CP4 EPSPS protein has also been reviewed by 

regulatory agencies around the world (OECD 1999, 2002). Furthermore, the U.S. EPA in 

1996 established an exemption from the requirement of a tolerance for residues of the 

plant pesticide inert ingredient CP4 EPSPS and the genetic material necessary for its 

production in all plants (40 CFR § 174.523, re-designated from § 180.1174, effective 

April 25, 2007). Prior safety assessments of the CP4 EPSPS protein expressed in these 

other modified crops are directly applicable to the MON 87429 CP4 EPSPS protein 

because the MON 87429 CP4 EPSPS protein is identical to the CP4 EPSPS proteins in 

these modified crops.
22

FT_T Protein

The ft_t gene in MON 87429 is a modified version of the R-2,4-

dichlorophenoxypropionate dioxygenase (Rdpa) gene from the soil bacteria Sphingobium 

herbicidovorans. The amino acid sequence of the FT_T protein shares ~ 89% sequence 

identity with wild type RdpA (Monsanto 2019). The FT_T protein is an alphaketoglutarate-dependent non-heme iron dioxygenase that catalyzes a dioxygenase 

reaction in the presence of alpha-ketoglutarate (αKG) and oxygen by incorporating 

oxygen into quizalofop, thus degrading it into the herbicidally-inactive quizalofop phenol 

and pyruvate. The FT_T protein also catalyzes the dioxygenase reaction that degrades 

auxin herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) into herbicidally-inactive 2,4-

dichlorophenol (2,4-DCP) and glyoxylic acid in the presence of alpha-ketoglutarate and 

oxygen. Thus, the FT_T protein in MON 87429 confers resistance to aryloxyalkanoate 

herbicides including the aryloxyphenoxypropionate acetyl coenzyme A carboxylase 

(ACCase) inhibitors (so called “FOPs” herbicides such as quizalofop) and some synthetic 

auxins, such as 2,4-D.

Monsanto demonstrated that the FT_T protein lacks structural similarity to allergens, 

toxins or other proteins known to produce adverse effects in mammals. The FT_T protein 

is rapidly digested by proteases found in the human gastrointestinal tract (pepsin and 

pancreatin) and demonstrated no acute oral toxicity in mice at the high dose tested. In 

addition, the ubiquitous presence of Sphingobium species in the environment has resulted 

in widespread human and animal exposure and is not commonly known for allergenicity 

and human or animal pathogenicity. Furthermore, the FT-T protein as an α-ketoglutaratedependent non-heme iron dioxygenase belongs to a diverse superfamily of Fe(II)/αketoglutarate dependent hydroxylases, and this protein superfamily is broadly distributed 

across the plant, animal and bacterial kingdoms, which have been extensively consumed 

by both humans and animals (Hausinger 2004) without any reports of adverse effects.

Therefore, it is unlikely that exposure to the FT_T protein in food and feed products 

derived from MON 87429 pose a risk to human and animal health.

Additionally, molecular characterization revealed no potential for unintended effects and 

no unintended changes to plant metabolism, as supported by the substantially equivalent 

compositional characteristics between MON 87429 and the conventional control. The 

germination and dormancy, phenotypic and agronomic, and pollen characteristics were 

not indicative of increased weediness or plant pest risk for MON 87429 compared to 

conventional maize. Furthermore, the arthropod and disease damages data showed a lack 

of differences in plant responses to a subset of non-target organisms (specific diseases 

and arthropod pests) between MON 87429 and conventional control maize. Similarly, 

there has been no reported adverse impacts to non-target organisms due to the exposure 

to DMO, PAT, or CP4 EPSPS proteins from either extensive testing and/or wide scale 

commercial cultivation of a number of different modified herbicide-resistant crops. The 

FT_T protein is unlikely to have adverse impacts to non-target organisms because of its 

non-toxic mode-of-action (MOA), lack of acute oral toxicity, and lack of impact on plant 

pest potential.
23

Corn possesses few of characteristics of weeds and has a long history of cultivation 

around the globe without any report that it is a serious weed or that it forms persistent 

feral populations. In the United States, the regions where maize is grown have no plants 

listed as threatened or endangered, or that are proposed for listing, that are sexually 

compatible with maize. Also, there are only a limited number of threatened or 

endangered species that may be found in U.S. maize fields, and there is an even more 

limited number of species that might feed on maize plants or maize grain. Furthermore, 

none of the listed species in states where maize is grown require maize as a host plant. 

The safety of the MON 87429 DMO, PAT, CP4 EPSPS and FT_T proteins, and the 

compositional, agronomic, and phenotypic equivalence of MON 87429 to conventional 

maize, support a conclusion that the planting of MON 87429 is not expected to affect 

listed threatened or endangered plant species or designated critical habitat for listed plant 

or animal species.

Therefore, based on the data including the mode of action, the low expression levels, and 

the molecular characterization and safety assessment of DMO, PAT, CP4 EPSPS and 

FT_T proteins; the demonstration of compositional, agronomic and phenotypic 

equivalence to conventional maize; and the environmental interactions assessment, 

APHIS concludes that exposure to and/or consumption of MON 87429 maize is unlikely 

to have any adverse impacts to non-target organisms, nor does it pose an additional risk 

to organisms beneficial to agriculture or threatened and endangered species compared to 

conventional maize.

F. Potential for Enhanced Weediness of MON 87429 maize

APHIS assessed whether the MON 87429 maize is likely to become weedier (i.e. more 

prevalent, competitive, damaging or difficult-to-control in situations where it is not 

wanted) than the unmodified progenitor from which it was derived, or other varieties of 

the crop currently under cultivation. The assessment considers the basic biology of maize, 

the situations in which maize volunteers or feral populations are considered weeds, and 

an evaluation of MON 87429 maize compared to conventional maize control and other 

reference maize hybrids for characteristics related to establishment, competiveness, 

reproduction, survival, persistence and/or spread that could influence weediness and the 

ability to manage the crop as a weed. For maize, such characteristics include seed 

dormancy and germination, agronomic and phenotypic traits, disease and pest 

susceptibility, and environmental interactions. The assessment also considers whether the 

stacked herbicide resistance trait affects methods of control for the crop in situations 

where it is managed as a weed or volunteer in subsequent crops or in feral populations.

In the United States, maize is not listed as a weed in the major weed references (Crockett

1977) and it is not designated as a noxious weed by the federal government (USDAAPHIS 2019b). Furthermore, maize does not possess weedy characteristics such as high 

level of seed dormancy, ease of seed shattering, and strong growth competitiveness 

(OECD 2003; OTGR 2008). Maize seeds do not exhibit dormancy and are well retained 

on the cob and covered by multiple layers of husk leaves. Also, maize is sensitive to low
24

temperatures, and the germinating seedlings and plants do not survive freezing winter 

conditions (OECD 2003; OTGR 2008) (Andersson and de Vicente 2010). Although 

maize seed does not shatter, harvest process or foraging wildlife can result in seed 

disperse, and some may overwinter and germinate when conditions are ideal and develop 

into volunteer plants the following year. However, maize has not been reported to be able 

to establish self-sustaining populations outside of cultivation (OECD 2003; OTGR 2008). 

This is further supported by data from controlled experiments where maize plants were 

left unharvested but no feral plants were discovered within a year or two after planting 

(Raybould et al. 2012; Sammons et al. 2014). Similar to conventional maize volunteers, 

MON 87429 maize volunteers can be managed by employing mechanical cultivation, 

crop rotation, and the careful selection of the modes of action for pre-emergent and postemergent herbicides to balance competing herbicide sensitivities between volunteers and 

the rotational crop (Vencill et al. 2012).

In comparative studies between MON 87429 and a conventional control, germination and 

dormancy, phenotypic and agronomic, environmental interaction (plant responses to 

abiotic stressors, diseases, and arthropod pests), and pollen characteristics were evaluated 

for changes that would impact the plant pest potential, and in particular, plant weediness 

potential. In each of these assessments, MON 87429 was compared to an appropriate 

conventional control that had a genetic background similar to MON 87429 but did not 

possess the inserted traits. In addition, multiple commercial maize hybrids developed 

through conventional breeding and selection were included to provide a range of 

comparative values for each characteristic that are representative of the variability in 

existing commercial maize hybrids.

To assess the seed germination and dormancy potential of MON 87429 maize seed, 

Monsanto conducted a comparative assessment of seed germination and dormancy 

characteristics for MON 87429 and the conventional control. MON 87429 was compared 

to the conventional control for percentages of germinated, dead, viable firm-swollen, and 

viable hard seed using two temperature regimes: optimum (alternating 20°C and 30°C) 

and suboptimum (constant 10°C for seven days followed by 25°C for four days). No 

statistically significant differences were detected between MON 87429 and the 

conventional control in either the optimum or suboptimum temperature regimes for any 

of the evaluated characteristics. These results demonstrate that the introduction of the 

dicamba-, glufosinate-, quizalofop-, and 2,4-D-tolerance and RHS traits does not result in 

different seed germination characteristics and dormancy potential of MON 87429 maize 

compared to conventional maize.

Monsanto also evaluated the phenotypic, agronomic, and environmental interactions 

characteristics of MON 87429 maize by comparing with the conventional control and 

four commercial reference hybrids at eight field sites representing major U.S. maize 

growing regions in 2017 (Monsanto, 2019). A combined-site analysis for nine phenotypic 

and agronomic characteristics (early stand count, days to flowering, plant height, days to 

maturity, lodging, final stand count, moisture, seed weight, and yield) showed no 

statistically significant differences between MON 87429 and the conventional control for 

any of the analyzed characteristics (Table VII-4, Monsanto 2019). Also, in an assessment
25

of plant responses to abiotic stressors (cold temperatures, drought, waterlogging, hail, 

high temperatures, high winds, nutrient deficiency, soil compaction, and sun scald), 

diseases (anthracnose, corn stunt, eyespot, Goss's bacterial wilt, gray leaf spot, leaf 

blight, northern leaf spot, rust, smut, and Stewart's wilt), and arthropod pests (aphids, 

armyworms, billbugs, corn earworms, corn flea beetles, corn rootworm beetles, 

cutworms, European corn borers, grasshoppers, Japanese beetles, sap beetles, slugs, 

spider mites, and stink bugs), no differences were observed between MON 87429 and the 

conventional control for any of the analyzed characteristics.

APHIS also assesses the potential for increased weedy or invasive characteristics of the 

sexually compatible plants and wild relatives through the potential gene flow and 

introgression from MON 87429 maize. The viability and morphology of MON 87429 

maize were compared to that of the conventional control and four commercial references 

grown under similar agronomic conditions. No statistically significant differences were 

detected between MON 87429 and the conventional control for percentage viable pollen, 

pollen diameter and general pollen morphology.

These results support the conclusion that MON 87429 does not possess: 1) increased 

weediness characteristics; 2) increased susceptibility or tolerance to specific abiotic 

stressors, diseases, or arthropod pests; or 3) characteristics that would confer a plant pest 

risk compared to conventional maize. Therefore, based on the results of multiple 

assessments discussed above and the weight of evidence supports the overall conclusion 

that the introduction of the dicamba-, glufosinate-, quizalofop-, and 2,4-D-tolerance and 

RHS traits does not result in increased weediness or plant pest risk of MON 87429 

compared to conventional maize and is unlikely to pose a plant pest risk. These results, in 

conjunction with the cultivation of existing various herbicide-resistant maize varieties in 

the United States, supports that MON 87429 maize is unlikely to be any more difficult to 

control as a volunteer in subsequent seasons after its planting. Thus, the existing 

numerous methods to effectively manage volunteer maize in agricultural fields (Ogg and

Parker 2000; USDA-APHIS 2014) are also likely to be effective in controlling 

MON87429 maize volunteers.

Based on the agronomic field data and literature survey concerning weediness potential 

of the crop, MON 87429 maize is unlikely to persist as a troublesome weed or to have an 

impact on current weed management practices. Furthermore, extensive post-harvest 

monitoring of field trial plots planted with MON 87429 maize under USDA-APHIS 

authorizations did not reveal any differences in survivability or persistence relative to 

other varieties of the same crop currently being grown. These data suggest that MON 

87429 maize is no more likely to become a weed than conventional varieties of the crop. 

MON 87429 maize volunteers and feral populations can be managed using a variety of 

currently available methods and alternative herbicides.
26

G. Potential Impacts on the Weediness of Any Other Plants with which 

MON 87429 maize Can Interbreed

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 (Grant 1981; Rieseberg and Wendel 1993; Soltis et al. 1993; 

Hegde et al. 2006), and even in the existing floras, the occurrence of hybridization or 

introgression is reported to be widespread (Stace 1987; Rieseberg and Wendel 1993; 

Peterson et al. 2002). It has been a common practice by plant breeders to artificially 

introgress traits from wild relatives into crop plants to develop new cultivars (Khoury et 

al. 2013). Hybridization and introgression are natural biological processes and do not 

constitute inherent environmental risks. However, gene flow from crops to wild relatives 

is also thought of as having a potential to enhance the weediness of wild relatives, as 

observed in rice, sorghum, sunflower and a few other crops (see Table 1 in (Ellstrand et

al. 1999)). This topic is covered in two sections: 1) the potential for gene flow, 

hybridization and introgression from the MON 87429 maize to sexually compatible 

relatives, including wild, weedy, feral or cultivated species in the United States and its 

territories, and 2) if so, the risk potential with respect to weediness of those taxa based on 

the phenotypic changes that have been observed in MON 87429 maize.

Potential for gene flow, hybridization, and gene introgression

Maize is a wind pollinated species with plant morphology and reproductive biology that 

facilitates cross pollination, leading to relatively high levels of pollen-mediated gene flow 

occurrence in this species. However, for pollen-mediated gene flow to occur between 

maize and its allied species and subspecies, certain conditions must be satisfied such as 

sexual compatibility, flowering synchrony and sufficient proximity to each other.

Hybridization with Teosinte

As described in Section B, the genus Zea consists of five species: 1) Z. diploperennis, 

perennial diploid (2n=20); 2) Z. luxurians, annual diploid (2n=20); 3) Z. nicaraguensis, 

annual diploid (2n=20); 4) Z. perennis, perennial tetraploid (2n=40); and the Z. mays, 

annual diploid (2n=20). The latter encompasses four annual diploid (2n=20) subspecies: 

ssp. mays, ssp. huehuetenangensis, ssp. mexicana and ssp. parviglumis (Hufford et al.

2012). Within genus Zea, Z. mays ssp. mays is the only domesticated maize and all the 

other species and subspecies are the wild relatives of the maize and are collectively 

named as teosintes (OTGR 2008; Andersson and de Vicente 2010).

All species in teosintes except the tetraploid perennial Z. perennis can cross with 

cultivated maize to produce fertile hybrids, but typically occur at very low rate (Doebley

1990; Baltazar et al. 2005; OTGR 2008). It is reported that hybridization between maize 

and Z. mays ssp. mexicana occurs sporadically and at very low rates (Baltazar et al. 2005; 

Ellstrand et al. 2007) but maize can hybridize with Z. mays ssp. parviglumis readily at 

higher rates (Ellstrand et al. 2007). However, while these hybridizations occurred in the
27

direction of maize as female and teosinte as male, hybridizations in the opposite direction 

rarely occurred (Ellstrand et al. 2007; Mauricio et al. 2013). Gene flow from maize to 

teosinte most probably results from crosses where teosinte first pollinates maize (Baltazar

et al. 2005). This limited and asymmetric gene flow, favoring teosinte introgression

into maize may be attributed to the genetic barrier between teosinte and maize that is 

controlled by a gene called the ‘Teosinte crossing barrier’ (Tcb) (Evans and Kermicle

2001). Gene flow and introgression between maize and teosintes is also limited by their 

geographical distribution, flowering synchrony and proximity.

Teosinte is not native to the United States. However, the annual teosinte (Z. mays ssp. 

mexicana) is reported to have feral populations in Florida, Alabama, and Maryland (USDANRCS 2019a) and Z. perennis is listed in Texas and South Carolina (USDA-NRCS

2019b). For Z. diploperennis and Z. luxurians, there are no reported information about 

their location and status in the United States (USDA-NRCS 2019c, 2019d). Experts 

familiar with the teosinte collections in the United States have been previously consulted 

and are not aware of the presence of any naturalized or native populations of teosintes in 

the United States (USDA-APHIS 2013).

Taken together, the genetic barrier, differences in developmental and morphological 

factors, potential flowering asynchrony and insufficient proximity between maize and 

teosinte as well as the limited geographical distribution of teosinte make natural crosses 

and gene introgression from MON 87429 maize into teosinte unlikely in the United 

States.

Hybridization with Tripsacum

Tripsacum is the genus that is the closet known relative of Zea and it consists of 16 

recognized species (OECD 2003). Tripsacum species has a base chromosome number of 

x=18 compared to the base chromosome of maize (x=10) and can be represented by 

diploid (2n=36), triploid (2n=54), tetraploid (2n=72), pentaploid (2n=90) and hexaploid 

(2n=108). There are five species of Tripsacum that are present in the United States, 

including three species native to the U.S.: T. floridanum (Florida gamagrass), T. 

lanceolatum (Mexican gamagrass), and T. dactyloides (Eastern gamagrass); two species 

introduced in Puerto Rico: T. latifolium (wideleaf gamagrass) and T. fasciculatum 

(Guatemalan gamagrass) (USDA-NRCS 2019e, 2019f, 2019g, 2019h, 2019i).

Unlike teosinte that its member species can hybridize with maize under natural 

conditions, out-crossing between maize and Tripsacum species is not known to occur in 

the wild and can only be made experimentally with extreme difficulty (OECD 2003).

Tripsacum species (T. dactyloides, T. floridanum, T. lanceolatum, and T. pilosum) have 

been crossed with maize under experimental conditions, however, the resultant hybrids 

have a high degree of sterility and are genetically unstable (Galinat 1988; OTGR 2008; 

Andersson and de Vicente 2010). Thus, Tripsacum species are unlikely to form viable 

hybrid progeny with maize under natural conditions.

The introduced genes encoding DMO, PAT, CP4 EPSPS and FT_T proteins in MON 

87429 maize are not expected to change the ability of the plant to interbreed with other
28

plant species. Indeed, the agronomic and phenotypic data of MON 87429 maize provided 

by Monsanto indicated no unintended changes likely to affect the potential gene flow 

from MON 87429 maize to sexually compatible species.

Based on all the above information, the genetic modification in MON 87429 maize is not 

expected to increase the potential for gene flow, hybridization and/or introgression to 

sexually-compatible taxa compared to the other maize varieties. Gene flow, hybridization 

and/or introgression of genes from MON 87429 maize to other sexually-compatible 

relatives with which it can interbreed is not likely to occur in the United States and its 

territories.

Potential for enhanced weediness of recipients after hybridization and/or introgression

Based on the data presented in the petition, MON 87429 maize does not exhibit 

characteristics that may cause it to be any weedier than other cultivated maize (Monsanto 

2019). Moreover, its potential impact due to the extremely limited potential for gene 

introgression into teosinte and Tripsacum species is not expected to be any different than 

that of other cultivated maize varieties. Additionally, none of the sexually compatiblerelatives of maize in the United States are considered to be weeds in the United States 

(Holm et al. 1979). Therefore, even in the extremely unlikely event of successful hybrids 

and/or introgression between MON 87429 maize and its wild relatives, the inserted 

transgenes of MON 87429 maize are unlikely to transform its wild relatives into more 

weedy species. If the maize wild relatives were introgressed with the herbicide resistance 

traits from MON 87429 maize, they can be managed using alternative herbicides and/or 

other method of weed control. Based on the above considerations, MON 87429 maize is 

unlikely to adversely impact sexually-compatible wild relatives or their weediness 

characters.

Based on the information presented in the petition and in relevant literature, APHIS has 

reached the following conclusions. The genetic modification in MON 87429 maize is not 

expected to increase the potential for gene flow, hybridization, and/or introgression to 

occur to sexually-compatible taxa compared to the non-modified recipient or other 

varieties of maize that are commonly grown. Gene flow, hybridization, and/or 

introgression of genes from MON 87429 maize to other sexually-compatible relatives, 

including wild, weedy, feral or cultivated species in the United States and its territories is 

not likely to occur. Furthermore, both the maize and its sexually compatible relative 

species are not considered weedy or invasive. The modified phenotype is not expected to 

affect the current ability to control these species in situations where they are considered 

weedy or invasive; the following measures are still available for their control: herbicides, 

tillage and other methods. Therefore, MON 87429 maize is not expected to increase the 

weed risk potential of other species with which it can interbreed in the United States and 

its territories.

H. Potential Changes to Agriculture or Cultivation Practices

APHIS assessed whether significant changes to agricultural or cultivation practices from 

adoption of the MON 87429 maize are likely to impact plant diseases or pests or their
29

management, including any APHIS control programs. This includes consideration of any 

changes in pesticide applications, tillage, irrigation, harvesting, etc. as they relate to plant 

pests and diseases.

As described in Section B, maize is widely grown in the world (Farnham et al. 2003; 

OTGR 2008), and it is grown in almost all the states in United States (USDA-NASS

2019a).Weeds, annual and/or perennial, are considered to be the greatest pest problem in 

maize production because they compete with maize for water, nutrients, and light 

resulting in substantial yield losses when left uncontrolled (Aref and Pike 1998). Weed 

management practices include mechanical practices (e.g., tillage), cultural practices (e.g., 

crop rotation, variety selection, optimizing planting date, plant population and row 

spacing), and chemical practices (e.g., herbicide application). Herbicide-Resistant maize 

is currently grown on approximately 90% of U.S. maize acres, and approximately 98% of 

the maize acreage in the U.S. receives an herbicide application (Monsanto 2019).

Numerous herbicides are available for preplant, preemergence, and postemergence 

control of annual and perennial weeds in maize (USDA-NASS 2019c-a). MON 87429 

maize offers the combination of dicamba, glufosinate, quizalofop, 2,4-D, and glyphosate 

resistance, and this combination will facilitate the utilization of multiple herbicide sitesof-action in a grower’s integrated weed management system to control a broad spectrum 

of grass and broadleaf weed species, including herbicide-resistant and tough to control 

weed species. Mon/N 87429 can help reduce the potential for further resistance 

development to glyphosate, dicamba, glufosinate, quizalofop and 2,4-D herbicides as 

well as other important maize herbicides.

It is noteworthy that the MON 87429 event confers glyphosate resistance in specific plant 

tissues (i.e., not in tassels) to facilitate the production of hybrid seed. The susceptibility of 

tassels in MON 87429 to glyphosate results in intended non-viable pollen phenotype 

when applying glyphosate during reproductive development. Glyphosate can also be used 

for weed control in MON 87429 inbred seed increases or hybrid seed production.

However, other agricultural management practices for the production of hybrid maize 

seed and for the cultivation of commercial maize would also be no different for MON 

87429 than for conventional maize hybrids. Furthermore, MON 87429 is not intended to 

be offered for commercial use as a stand-alone product, but will be combined, through 

traditional breeding methods, with other deregulated events that confer full-plant 

glyphosate resistance (e.g., NK603). Upon stacking of MON 87429 maize with 

deregulated full-plant glyphosate resistance traits, growers will have the ability to use the 

established current glyphosate practice for weed control.

Glufosinate, quizalofop and 2,4-D herbicides are currently labeled for preplant 

applications on conventional and herbicide-resistant maize hybrids and for in-crop 

postemergence applications on herbicide-resistant (HR) hybrids. The intended preplant 

and postemergence uses of these herbicides with MON 87429 maize would not be any 

different than current labeled uses in HR maize. In support of Monsanto’s new herbicide 

resistant product MON 87419 maize that has been deregulated by USDA-APHIS, 

Monsanto requested that EPA allow the 0.5 lb a.e./ac postemergence application window 

for dicamba to be extended from V5 to V8 growth stage or 36-inch height of maize,
30

whichever occurs first (U.S. EPA, 2019). Pending approval of the expanded label at EPA, 

the dicamba use pattern for MON 87429 would be no different than that of MON 87419.

Therefore, it is not anticipated that commercialization of MON 87429 maize in the U.S. 

would have a notable impact on current maize production practices, beyond the intended 

benefits of effective management of common, troublesome weeds, and/or herbicideresistant weeds and additional options for growers to rotate and/or use combinations of 

herbicides with multiple sites-of-action for preplant and in-crop postemergence herbicide 

applications.

Herbicides can impact pests or pathogens directly or indirectly through effects on the 

control of the crop or weeds associated with the crop. The issue of whether glyphosate 

use in glyphosate resistant plants increases disease severity has been addressed in a recent 

review article (Duke et al. 2012). For crops where no-till or conservation tillage have not 

been widely used, the wide-spread adoption of post-emergent herbicides in the crop 

might increase use of conservation tillage practices which could impact diseases that 

build up in crop residue left on the soil (Duke et al. 2012). Data provided within the 

Monsanto petition shows that MON 87429 maize is phenotypically similar to 

conventional maize and is no more susceptible to diseases or pests than commercially 

cultivated maize. Thus, MON 87429 maize is unlikely to exacerbate plant pests or 

diseases associated with maize. As a result, APHIS does not foresee changes in either 

insects or disease damage or control measures employed due to agricultural or cultivation 

practices with MON 87429 maize.

Information contained within the Monsanto petition demonstrates that except for greater 

diversity in herbicide chemistry resistance that will provide greater flexibility in weed 

control options, there are no expected changes to the inputs needed for MON 87429 

maize production, and no expected impacts to most of the agronomic practices employed 

for production of maize compared to the current practices. The cultivation practices 

needed for growing MON 87429 maize are similar to that used to grow conventional 

maize. Additionally, 38 modified maize varieties have been previously evaluated and 

determined to be no longer subject to the regulatory requirements of 7 CFR part 340 or 

the plant pest provisions of the Plant Protection Act, in part due to an absence of these 

introduced traits to substantially alter maize cultivation practices (USDA-APHIS 2019a).

APHIS could not identify any significant changes to agricultural or cultivation practices 

(e.g. pesticide applications, tillage, irrigation, harvesting, etc.) from adoption of MON 

87429 maize; therefore, no impact on plant diseases or pests, or their management is 

likely to occur.

I. Potential Impacts from Transfer of Genetic Information to 

Organisms with which MON 87429 maize Cannot Interbreed

APHIS examined the potential for the new genetic material inserted into MON 87429 

maize to be horizontally transferred without sexual reproduction to other organisms and 

whether such an event could lead directly or indirectly to disease, damage, injury or harm
31

to plants, including the creation of new or more virulent pests, pathogens, or parasitic 

plants. The horizontal gene transfer between unrelated organisms is one of the most 

intensively studied fields in the biosciences since 1940, and the issue gained extra 

attention with the release of modified plants into the environment (Dröge et al. 1998). 

Potential risks from stable horizontal gene transfer (HGT) from modified organisms to 

another organism without reproduction or human intervention were recently reviewed 

(Keese 2008). Mechanisms of HGT include conjugation, transformation and transduction, 

and other diverse mechanisms of DNA and RNA uptake, recombination, and 

rearrangement, most notably through viruses and mobile genetic elements. HGT has been 

a major contributor to the spread of antibiotic resistance amongst pathogenic bacteria; 

emergence of increased virulence in bacteria, eukaryotes and viruses; and, in the long run, 

to major transitions in evolution (Brown 2003; Keeling and Palmer 2008; Keese 2008).

Potential for horizontal gene transfer to bacteria, fungi, or invertebrates

MON 87429 maize contains tandemly arrayed four gene expression cassettes for the 

expression of genes pat, dmo, ft_t, and cp4 epsps with in total 20 genetic elements 

derived from plants, bacteria and plant virus.

HGT and expression of DNA from a plant species to bacterial, fungal or invertebrate 

species is unlikely to occur based on the following observations. Although there are many 

opportunities for plants to directly interact with fungi and bacteria (e.g., as commensals, 

symbionts, parasites, pathogens, decomposers, or in the guts of herbivores) and with 

invertebrates as plant pests, there are almost no evolutionary examples of HGT from 

eukaryotes to bacteria or from plants to fungi or invertebrates (Keese 2008). Examples of 

HGT between eukaryotes and fungi primarily involve gene acquisition or transfer by 

fungi to or from other distantly related fungi or bacteria (Keeling and Palmer 2008; Keese

2008) and HGT between plants and fungi is extremely rare (Richards et al. 2009).

Examples of HGT between plants and invertebrates are also extremely rare, and most 

examples of HGT in insects involve acquisition of genes from their pathogens or 

endosymbionts (Keese 2008; Zhu et al. 2011; Acuna et al. 2012).

Horizontal gene transfer from and expression in bacteria of the foreign DNA inserted into 

the nuclear genome of the modified plant is unlikely to occur. First, many genomes (or 

parts thereof) have been sequenced from bacteria that are closely associated with plants 

including Agrobacterium and Rhizobium (Wood et al. 2001; Kaneko et al. 2002). There is 

no evidence that these organisms contain genes derived from plants. HGT from plants to 

bacteria is a very low frequency event, primarily because functional and selective barriers 

to HGT increase with genetic distance (Keese 2008). Second, in cases where review of 

sequence data implied that horizontal gene transfer occurred, these events are inferred to 

occur on an evolutionary time scale on the order of millions of years (Koonin et al. 2001; 

Brown 2003; EFSA 2009). Third, transgene DNA promoters and coding sequences are 

optimized for plant expression, not prokaryotic bacterial expression. Thus, even if 

horizontal gene transfer occurred, proteins corresponding to the transgenes are not likely 

to be produced. Fourth, both the US-FDA (US-FDA 1998) and the European Food Safety
32

Authority (EFSA 2009) have evaluated horizontal gene transfer from the use of 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 very rare or remote.

Potential for horizontal gene transfer to viruses

APHIS also considered whether horizontal transfer of DNA from the modified plant to 

plant viruses was likely to occur and would lead to the creation or selection of plant 

viruses that are more virulent or have a broader host range. This issue has been 

considered before by other science review panels and government regulatory bodies 

(EPA-FIFRA-SAP 2006; Keese 2008). HGT is not unusual among plant viruses; 

however, this is generally limited to exchange between viruses present in the same host 

organism in mixed infections, and most commonly involves homologous recombination, 

relying on sequence similarity at the point of crossover (Keese 2008). HGT from virus 

sequences engineered into plants has been demonstrated with infecting or challenge 

viruses, including both DNA viruses (e.g., geminiviruses which replicate in the nucleus) 

(Frischmuth and Stanley 1998) and RNA viruses (which typically replicate in the 

cytoplasm); however most have been under conditions that favor recombination to restore 

a defective virus (Fuchs and Gonsalves 2007; Keese 2008; Thompson and Tepfer 2010). 

Populations of recombinants between virus transgenes expressed in modified plants 

infected with related viruses are similar to recombinants found in mixed infections of the 

same viruses in non-modified plants, indicating that there was no novel recombination 

mechanism in the modified plants and no increased risk is expected over what is expected 

from mixed infections (Keese 2008; Turturo et al. 2008). Nonhomologous recombination 

in HGT among viruses or between virus transgenes and infecting viruses can occur, but 

frequently results in gene deletions which can result in nonviable viruses (Morroni et al.

2013). Depending on the particular virus and sequences involved, various hot spots for 

recombination have been found in both coding and noncoding regions, and strategies 

implemented in design of transgenes to avoid recombination have been suggested. No 

recombinant or undesirable viruses with new properties have been detected for over at 

least 8-10 years in field tests or during commercial growth of deregulated virus resistant 

plum, squash, or papaya engineered with genes from viruses that have been deregulated 

in the U.S. (Fuchs and Gonsalves 2007).

Potential for horizontal gene transfer to parasitic plants

Evidence for HGT from plants to other plants is limited to two specific scenarios: (1) 

exchange of genes between a parasitic plant and its host; and (2) exchange of genes 

between cells of two plants living in close proximity, such as in a graft junction. In both 

cases, this type of HGT requires physical contacts between the two plants. Most cases of 

HGT in plants involve transfer of mitochondrial genomes, which are primarily maternally 

inherited in plants (Barr et al. 2005), to other mitochondria genomes, and mostly involve 

parasitic plants and their hosts (Richardson and Palmer 2007). Recently, a comparative 

genomics analysis implicated HGT for the incorporation of a specific genetic sequence in 

the parasitic plant purple witchweed (Striga hermonthica) from its monocot host plant
33

(Yoshida et al. 2010). According to this study, the incorporation of the specific genetic 

sequence (with an unknown function) occurred between sorghum and purple witchweed. 

However, this HGT occurred before speciation of purple witchweed and related cowpea 

witchweed (S. gesnerioides) from their common ancestor. Furthermore, S. hermonthica is 

not found in the U.S. and S. asiatica, another related parasite of cereal crops, is only 

present in North Carolina and South Carolina (USDA-NRCS 2019j). More recent studies 

demonstrated that in a few parasitic species of the Rafflesiaceae family, out of several 

genetic sequences examined, about 2.1% of nuclear (Xi et al. 2012) and 24 –41% of 

mitochondrial (Xi et al. 2013) gene transcripts appeared to be acquired from their 

obligate host species. However, all the above-mentioned instances of HGT between 

parasitic plants and their hosts were reported to be of ancient origins, on an evolutionary 

time scale spanning thousands to millions of years ago. Furthermore, in MON 87429 

maize, the DNA sequences were inserted into the nuclear genome, not the mitochondrial 

genome (Monsanto 2019).

If MON 87429 maize becomes infected by a parasitic plant or is naturally grafted to 

another plant, there is a very low probability that HGT could result in the other plant 

acquiring DNA from MON 87429 maize. However, in both scenarios this newly 

introduced DNA would likely reside in somatic cells, and with little chance of reaching 

the germ cells, this introduced DNA could not persist in subsequent generations unless 

the recipient plant reproduced asexually from the affected cells.

Based on the above analysis, APHIS therefore concludes that HGT of the new genetic 

material inserted into MON 87429 maize to other organisms is highly unlikely and is not 

expected to lead directly or indirectly to disease, damage, injury or harm to plants, 

including the creation of new or more virulent pests, pathogens, or parasitic plants.

J. Conclusion

APHIS has reviewed the information submitted in the petition, supporting documents, 

public comments in response to Federal Register notices concerning this petition, and 

other relevant information to assess the plant pest risk of MON 87429 maize compared to 

the unmodified variety from which it was derived. APHIS concludes that the MON 

87429 maize is unlikely to pose a greater plant pest risk compared to the unmodified 

variety from which it was derived based on the following findings.

• No plant pest risk was identified from the transformation process or the insertion of 

new genetic material in MON 87429 maize because the A. tumefaciens transformation 

vector was disarmed, the transformed material was treated with an antibiotic to kill 

the bacterium, and the inserted plant pest sequences do not cause disease or create an 

infectious agent.

• No increase in plant pest risk was identified in MON 87429 maize from expression of 

the inserted genetic materials, or changes in metabolism or composition because there 

were no significant changes in agronomic, ecological and compositional 

characteristics that would render MON 87429 maize more susceptible to pests and 

diseases over its control or reference maize varieties.
34

• Disease and pest incidence and/or damage were not observed to be significantly 

increased or atypical in MON 87429 maize compared to the unmodified counterpart 

or other comparators in field trials conducted in growing regions representative of 

where MON 87429 maize is expected to be grown. Observed agronomic traits also 

did not reveal any significant differences that would indirectly indicate that MON 

87429 maize is more susceptible to pests or diseases. Therefore, no plant pest effects 

are expected on these or other agricultural products and no impacts are expected to 

APHIS pest control programs.

• Exposure to and/or consumption of MON 87429 maize is unlikely to have any 

adverse impacts on organisms beneficial to agriculture based on the analysis of 

studies on MON 87429 maize food and feed safety and composition. 

• MON 87429 maize is no more likely to become a weed or become weedier than 

conventional varieties of the crop based on its observed agronomic characteristics, 

weediness potential of the crop and current management practices available to control 

MON 87429 maize as a weed. Volunteers and feral populations of MON 87429 maize 

can be managed using a variety of currently available methods and herbicides. 

• MON 87429 maize is not expected to increase the weed risk potential of other species 

with which it can interbreed in the U.S. or its territories. Gene flow, hybridization 

and/or introgression of inserted genes from MON 87429 maize to other sexually 

compatible relatives with which it can interbreed is not likely to occur. The sexual 

compatible relatives of maize are not considered weedy or invasive, and the new 

phenotype conferred by genetic engineering is not likely to increase the weediness of 

these sexually compatible relatives or affect the current ability to control these 

relatives in situations where they are considered weedy or invasive.

• Significant changes to agricultural or cultivation practices (e.g. pesticide applications, 

tillage, irrigation, harvesting, etc.) from adoption of MON 87429 maize were not 

identified and are not likely to increase plant diseases or pests or compromise their 

management.

• Horizontal gene transfer of the new genetic material inserted into MON 87429 maize 

to other organisms is highly unlikely and is not expected to lead directly or indirectly 

to disease, damage, injury or harm to plants, including the creation of new or more 

virulent pests, pathogens, or parasitic plants. 

K. References

51 FR 23302. 1986. Coordinated Framework for Regulation of Biotechnology. 

57 FR 22984. 1992. Statement of Policy: Foods Derived from New Plant Varieties. 

Acuna R, Padilla BE, Florez-Ramos CP, Rubio JD, Herrera JC, Benavides P, Lee SJ,

Yeats TH, Egan AN, Doyle JJ, and Rose JK. 2012. Adaptive horizontal transfer of 

a bacterial gene to an invasive insect pest of coffee. PNAS 109, pp. 4197-4202. 

Retrieved from 

http://www.pnas.org/content/early/2012/02/17/1121190109.abstract

Alibhai MF and Stallings WC. 2001. Closing down on glyphosate inhibition-with a new 

structure for drug discovery. Proceedings of the National Academy of Sciences of 

the United States of America 98, pp. 2944-2966. 
35

Anderson JE, Michno JM, Kono TJ, Stec AO, Campbell BW, Curtin SJ, and Stupar RM. 

2016. Genomic variation and DNA repair associated with soybean transgenesis: 

a comparison to cultivars and mutagenized plants. BMC biotechnology 16, pp. 

41. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/27176220

Andersson MS and de Vicente MC. 2010. Maize, Corn (Zea mays L.). In: Gene Flow

between Crops and Their Wild Relatives (The Johns Hopkins University Press),

pp. 255 - 291.

Aref S and Pike DR. 1998. Midwest Farmers’ Perceptions of Crop Pest Infestation. 

Agronomy Journal 90, pp. 819-825.

Baltazar BM, de Jesus Sanchez-Gonzalez J, de la Cruz-Larios L, and Schoper JB. 2005. 

Pollination between maize and teosinte: an important determinant of gene flow in 

Mexico. Theor Appl Genet 110, pp. 519-526. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/15592808

Barr CM, Neiman M, and Taylor DR. 2005. Inheritance and recombination of 

mitochondrial genomes in plants, fungi and animals. New Phytologist 168, pp. 

39-50. Retrieved from http://onlinelibrary.wiley.com/doi/10.1111/j.1469-

8137.2005.01492.x/abstract

Brown JR. 2003. Ancient horizontal gene transfer. Nature reviews. Genetics 4, pp. 121- 

132. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/12560809

Chakraborty S, Behrens M, Herman PL, Arendsen AF, Hagen WR, Carlson DL, Wang

XZ, and Weeks DP. 2005. A three-component dicamba O-demethylase from 

Pseudomonas maltophilia, strain DI-6: purification and characterization. 

Archives of biochemistry and biophysics 437, pp. 20-28. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/15820213

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

Hawaii Press.

Doebley J. 1990. Molecular Evidence for Gene Flow among Zea Species. BioScience 40,

pp. 443-448.

Dröge M, Puhler A, and Selbitschka W. 1998. Horizontal gene transfer as a biosafety 

issue: A natural phenomenon of public concern. Journal of Biotechnology 64, pp. 

75–90. Retrieved from 

http://www.sciencedirect.com/science/article/pii/S0168165698001059

Duke SO. 2005. Taking stock of herbicide-resistant crops ten years after introduction. 

Pest management science 61, pp. 211-218. Retrieved from

EFSA. 2009. Statement of EFSA on the consolidated presentation of opinions on the use 

of antibiotic resistance genes as marker genes in genetically modified plants. 

EFSA Journal 1108. Retrieved from 

http://www.efsa.europa.eu/en/efsajournal/pub/1108.htm

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

domesticated plants into their wild relatives. Annual Review of Ecology and 

Systematics 30, pp. 539-563. Retrieved from 

http://www.annualreviews.org/doi/abs/10.1146%2Fannurev.ecolsys.30.1.539

Ellstrand NC, Garner LC, Hegde S, Guadagnuolo R, and Blancas L. 2007. Spontaneous 

Hybridization between Maize and Teosinte. Journal of Heredity 98, pp. 183-187.
36

EPA-FIFRA-SAP. 2006. Plant Incorporated Protectants Based on Virus Coat Protein 

Genes: Science Issues Asosciated with the Proposed Rule. Retrieved from 

http://www.epa.gov/scipoly/sap/meetings/2005/december/minutes1205.pdf

Evans MMS and Kermicle JL. 2001. Teosinte crossing barrier1, a locus governing 

hybridization of teosinte with maize. Theor Appl Genet 103, pp. 259-265. 

FAO-WHO. 2010. Pesticide residues in food 2010. 

FAOSTAT. 2019. Worldwide cereal total productions. Food and Agriculture 

Organization of the United Nations. 

Farnham DE, Benson GO, and Pearce RB. 2003. Corn Perspective and Culture. In: Corn: 

Chemistry and Technology (St. Paul, Minnesota: American Association of Cereal 

Chemists, Inc.), pp. 1-33. 

Frischmuth T and Stanley J. 1998. Recombination between viral DNA and the transgenic 

coat protein gene of African cassava mosaic geminivirus. Journal of General 

Virology 79, pp. 1265-1271. Retrieved from 

https://jgv.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-79- 

5-1265#tab2

Fuchs M and Gonsalves D. 2007. Safety of virus-resistant transgenic plants two decades 

after their introduction: lessons from realistic field risk assessment studies. 

Annual Review of Phytopathology 45, pp. 173-202. Retrieved from 

http://www.annualreviews.org/doi/full/10.1146/annurev.phyto.45.062806.094434

?url_ver=Z39.88-2003

Galinat WC. 1988. Corn and Corn Improvement. In: Agronomy (Madison, Wisconsin: 

American Society of Agronomy, Crop Science Society of America, Soil Science 

Society of America), pp. 1-31. 

Gelvin SB. 2003. Agrobacterium-mediated plant transformation: the biology behind the 

"gene-jockeying" tool. Microbiology and molecular biology reviews : MMBR 67, 

pp. 16-37, table of contents. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/12626681

Grant V. 1981. Plant Speciation. Columbia University Press.

Harayama S, Kok M, and Neidle EL. 1992. Functional and evolutionary relationship 

among oxygenases. Annual Review of Microbiology 46, pp. 565-601. 

Hausinger RP. 2004. FeII/alpha-ketoglutarate-dependent hydroxylases and related 

enzymes. Critical reviews in biochemistry and molecular biology 39, pp. 21-68. 

Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/15121720

Hegde SG, Nason JD, Clegg JM, and Ellstrand NC. 2006. The Evolution of California's 

Wild Radish Has Resulted in the Extinction of Its Progenitors. Evolution 60, pp. 

1187. Retrieved from http://www.bioone.org/doi/abs/10.1554/05-

634.1#.Uhelsxtwq-x

Herman RA and Price WD. 2013. Unintended compositional changes in genetically 

modified (GM) crops: 20 years of research. Journal of agricultural and food 

chemistry 61, pp. 11695-11701. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/23414177

Holm LG, Pancho JV, Herberger JP, and Plucknett D. 1979. A Geographical Atlas of 

World Weeds. New York: John Wiley and Sons. 
37

Hufford MB, Bilinski P, Pyhäjärvi T, and Ross-Ibarra J. 2012. Teosinte as a model 

system for population and ecological genomics. Trends in Genetics 28, pp. 606- 

615.

ILSI. 2010. A Review of the Environmental Safety of the CP4 EPSPS Protein. 

Washington D.C.

Kaneko T, Nakamura Y, Sato S, Minamisawa K, T. U, Sasamoto S, Watanabe A, 

Idesawa K, Irigushi M, Kawashima K, Kohara M, Matsumoto M, Shimpo S, 

Tsuruoka H, Wada T, Yamada M, and Tabats S. 2002. Complete Genomic 

Sequence of Nitrogen-fixing Symbiotic Bacterium Bradyrhizobium japonicum 

USDA110. DNA Research 9, pp. 189-197. Retrieved from 

http://dnaresearch.oxfordjournals.org/content/9/6/189.long > 

Keeling PJ and Palmer JD. 2008. Horizontal gene transfer in eukaryotic evolution. 

Nature reviews. Genetics 9, pp. 605-618. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/18591983

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

Biosafety Research 7, pp. 123-149. Retrieved from 

https://www.ncbi.nlm.nih.gov/pubmed/18801324

Khoury CK, Greene S, Wiersema J, Maxted N, Jarvis A, and Struik PC. 2013. An 

Inventory of Crop Wild Relatives of the United States. Crop Science 53, pp. 1496. 

Retrieved from https://www.crops.org/publications/cs/abstracts/53/4/1496

Koonin EV, Makarova KS, and Aravind L. 2001. Horizonal Gene Transfer in 

Prokaryotes: Quantification and Classification. Annual Review of Microbiology 

55, pp. 709-742. Retrieved from 

http://www.annualreviews.org/doi/full/10.1146/annurev.micro.55.1.709?url_ver=

Z39.88-2003

Mauricio R, Hufford MB, Lubinksy P, Pyhäjärvi T, Devengenzo MT, Ellstrand NC, and 

Ross-Ibarra J. 2013. The Genomic Signature of Crop-Wild Introgression in Maize. 

PLoS Genetics 9, pp. e1003477. 

Morroni M, Jacquemond M, and Tepfer M. 2013. Deep sequencing of recombinant virus 

populations in transgenic and nontransgenic plants infected with Cucumber 

mosaic virus. Molecular Plant-Microbe Interactions 26, pp. 801-811. Retrieved 

from http://apsjournals.apsnet.org/doi/abs/10.1094/MPMI-02-13-0057-

R?url_ver=Z39.88-2003

OECD. 1999. Consensus Document on General Information Concerning the Genes and 

Their Enzymes that Confer Tolerance to Phosphinothricin Herbicide. 

OECD. 2002. Consensus Document on Compositional Considerations for New Varieties 

of Maize (Zea mays): Key Food and Feed Nutrients, Anti-nutrients and Secondary 

Plant Metabolites.

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

Paris. Organisation for Economic Co-operation and Development.

Ogg AG and Parker R. 2000. Control of Volunteer Crop Plants. 

OTGR. 2008. The Biology of Zea mays L. ssp mays (maize or corn). Australian 

Government/Office of the Gene Technology Regulator. 

Peterson CD, Pearman DA, and Dines TD. 2002. New Atlas of the British flora. Oxford 

University Press.
38

Raybould A, Higgins LS, Horak MJ, Layton RJ, Storer NP, De La Fuente JM, and 

Herman RA. 2012. Assessing the ecological risks from the persistence and spread 

of feral populations of insect-resistant transgenic maize. Transgenic research 21, 

pp. 655-664. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/22002083

Richards TA, Soanes DM, Foster PG, Leonard G, Thornton CR, and Talbot NJ. 2009.

Phylogenomic analysis demonstrates a pattern of rare and ancient horizontal 

gene transfer between plants and fungi. Plant Cell 21, pp. 1897-1911. Retrieved 

from http://www.plantcell.org/content/21/7/1897.long

Richardson AO and Palmer JD. 2007. Horizontal gene transfer in plants. Journal of 

Experimental Botany 58, pp. 1-9. Retrieved from 

http://jxb.oxfordjournals.org/content/58/1/1.long

Rieseberg LH and Wendel JF. 1993. Introgression and its consequences in plants. In: 

Hybrid Zones and the Evolutionary Process (Oxford University Press), pp. 70- 

109.

Salomon S and H. P. 1998. Capture of genomic and T-DNA sequences during doublestrand break repair in somatic plant cells. The EMBO Journal 17, pp. 6086-6095. 

Sammons B, Whitsel J, Stork LG, Reeves W, and Horak M. 2014. Characterization of 

Drought-Tolerant Maize MON 87460 for Use in Environmental Risk Assessment. 

Crop Science 54, pp. 719-729. 

Sikorski JA and Gruys KJ. 1997. Understanding Glyphosate’s Molecular Mode of Action 

with EPSP Synthase: Evidence Favoring an Allosteric Inhibitor Model. Accounts 

of Chemical Research 30, pp. 2-8. 

Soltis DE, Soltis PS, and Rieseberg LH. 1993. Molecular Data and the Dynamic Nature 

of Polyploidy. Critical Reviews in Plant Sciences 12, pp. 243-273. Retrieved from 

http://www.tandfonline.com/doi/abs/10.1080/07352689309701903#.UhekuRtwqw

Stace CA. 1987. Hybridization and the plant species. 

Steinrucken HC and Amrhein N. 1980. The herbicide glyphosate is a potent inhibitor of 

5-enolpyruvyl-shikimin acid-3-phosphate synthase. Biochemical and Biophysical 

Research Communications 94, pp. 1207-1212. 

Thompson CJ, Movval NR, Tizard R, Crameri R, Davies JE, Lauwereys M, and 

Botterman J. 1987. Characterization of the herbicide-resistance gene bar from 

Streptomyces hygroscopicus. The EMBO Journal 6, pp. 2519-2523. 

Thompson DV and Tepfer M. 2010. Assessement of the Benefits and Risksfor Engineered 

Virus Resistance. Advances in Virus Research 76, pp. 33-55. 

Turturo C, Friscina A, Gaubert S, Jacquemond M, Thompson JR, and Tepfer M. 2008. 

Evaluation of potential risks associated with recombination in transgenic plants 

expressing viral sequences. The Journal of General Virology 89, pp. 327-335. 

Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/18089757

US-EPA. 1999. Phosphinothricin Acetyltransferase and the Genetic Material Necessary 

for Its Production in All Plants; Exemption From the Requirement of a Tolerance 

On All Raw Agricultural Commodities. 

US-EPA. 2019. Federal Register Pesticide Product Registration - Notice for dicamba 

new uses.

US-FDA. 1998. Guidance for Industry: Use of Antibiotic Resistance Marker Genes in 

Transgenic Plants. 
39

US-FDA. 2006. Guidance for Industry: Recommendations for the Early Food Safety 

Evaluation of New Non-Pesticidal Proteins Produced by New Plant Varieties 

Intended for Food Use. 

USDA-APHIS. 2013. Plant Pest Risk Assessment for HCEM485 Corn. Retrieved from 

https://www.aphis.usda.gov/brs/aphisdocs/09_06301p_fpra.pdf;

https://www.aphis.usda.gov/aphis/ourfocus/biotechnology/permits-notificationspetitions/petitions/petition-status

USDA-APHIS. 2014. Weed Risk Assessments for Zea mays L. subsp. mays (Poaceae) – 

Maize and Genetically Engineered Herbicide-Resistant Maize. 

USDA-APHIS. 2019a. Petitions for Determination of Nonregulated Status of GE Corn. 

United States Department of Agriculture.

USDA-APHIS. 2019b. Plant Pest and Disease Programs. Retrieved from 

https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-diseaseprograms

USDA-FAS. 2019. World Agricultural Production. United States Department of 

Agriculture/Foreign Agricultural Service.

USDA-NASS. 2019a. Maize Harvested Acreage & Change from Previous Year by State 

in the U.S. USDA-National Agricultural Statistics Service.

USDA-NASS. 2019b. Maize Production Areas in the u.s. USDA-National Agricultural 

Statistics Service.

USDA-NASS. 2019c-a. Agricultural Chemical Uses Survey. 

USDA-NASS. 2019c-b. Maize Yield by Year in the U.S. USDA-National Agricultural 

Statistics Service.

USDA-NRCS. 2019a. Zea mays ssp. mexicana. The Plants Database. National Plant Data 

Team, Greensboro, Nc 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=ZEME

USDA-NRCS. 2019b. Zea perennis. The PLANTS Database. National Plant Data Center, 

Greensboro, NC 27401-4901. USA. Retrieved from 

https://plants.sc.egov.usda.gov/core/profile?symbol=ZEPE

USDA-NRCS. 2019c. Zea diploperennis. The PLANTS Database. National Plant Data 

Center, Greensboro, NC 27401-4901. USA. Retrieved from 

https://plants.sc.egov.usda.gov/core/profile?symbol=ZEDI

USDA-NRCS. 2019d. Zea luxurians. The PLANTS Database. National Plant Data 

Center, Greensboro, NC 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=ZELU

USDA-NRCS. 2019e. Tripsacum floridatum. The PLANTS Database. National Plant 

Data Center, Greensboro, NC 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=TRFL4

USDA-NRCS. 2019f. Tripsacum lanceolatum. The PLANTS Database. National Plant 

Data Center, Greensboro, NC 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=TRLA11

USDA-NRCS. 2019g. Tripsacum dactyloides. The PLANTS Database. National Plant 

Data Center, Greensboro, NC 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=TRDA3
40

USDA-NRCS. 2019h. Tripsacum latifolium. The PLANTS Database, National Plant Data 

Center, Greensboro, NC 27301-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=TRLA24

USDA-NRCS. 2019i. Tripsacum fasciculatum. The PLANTS Database. National Plant 

Data Center, Grensboro, NC 27401-4901. USA. Retrieved from 

http://plants.usda.gov/core/profile?symbol=TRFA2

USDA-NRCS. 2019j. Striga asiatica (L.) Kuntze, Asiatic witchweed. The PLANTS 

Database. National Plant Data Center, Grensboro, NC 27401-4901. USA. 

Retrieved from https://plants.usda.gov/core/profile?symbol=STAS2 Last 

accessed March 11, 2015. 

Vencill WK, Nichols RL, Webster TM, Soteres JK, Mallory-Smith C, Burgos NR, 

Johnson WG, and McClelland MR. 2012. Herbicide resistance: Toward an 

understanding of resistance development and the impact of herbicide-resistant 

crops. Weed Science 60(sp1):2-30. Retrieved from 

http://www.wssajournals.org/doi/abs/10.1614/WS-D-11-00206.1

Venkatesh TV, Harrigan GG, Perez T, and Flint-Garcia S. 2015. Compositional 

assessments of key maize populations: B73 hybrids of the Nested Association 

Mapping founder lines and diverse landrace inbred lines. Journal of agricultural 

and food chemistry 63, pp. 5282-5295. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/25966324

Wohllehen W, Arnold W, Broer I, Hillemaan D, Strauch E, and Puhler A. 1988.

Nucleotide sequence of the phosphinnthricin IV-acetyltransferase gene from 

Streptomyces viridoehromogenes Tii494 and its expression in Nicotiana tabacum. 

Gene 70, pp. 25-37. 

Wood DW, Setubal JC, Kaul R, Monks DE, Kitajima JP, Okura VK, Zhou Y, Chen L, 

Wood GE, Almeida NF, Jr., Woo L, Chen Y, Paulsen IT, Eisen JA, Karp PD, 

Bovee D, Sr., Chapman P, Clendenning J, Deatherage G, Gillet W, Grant C, 

Kutyavin T, Levy R, Li MJ, McClelland E, Palmieri A, Raymond C, Rouse G, 

Saenphimmachak C, Wu Z, Romero P, Gordon D, Zhang S, Yoo H, Tao Y, 

Biddle P, Jung M, Krespan W, Perry M, Gordon-Kamm B, Liao L, Kim S, 

Hendrick C, Zhao ZY, Dolan M, Chumley F, Tingey SV, Tomb JF, Gordon MP, 

Olson MV, and Nester EW. 2001. The genome of the natural genetic engineer 

Agrobacterium tumefaciens C58. Science 294, pp. 2317-2323. Retrieved from 

http://www.sciencemag.org/content/294/5550/2317.long

Xi S, Bradley RB, Wurdack KJ, Wong KM, Sugumaran M, Bomblies K, Rest JS, and 

Davis CC. 2012. Horizontal transfer of expressed genes in a parasitic flowering 

plant. BMC Genomics. Retrieved from http://www.biomedcentral.com/1471-

2164/13/227

Xi Z, Wang Y, Bradley RK, Sugumaran M, Marx CJ, Rest JS, and Davis CC. 2013.

Massive mitochondrial gene transfer in a parasitic flowering plant clade. PLoS 

Genetics 9. Retrieved from 

http://www.plosgenetics.org/article/info%3Adoi%2F10.1371%2Fjournal.pgen.10

03265

Yoshida S, Maruyama S, Nozaki H, and Shirasu K. 2010. Horizontal Gene Transfer by 

the Parasitic Plant Striga hermonthica. Science 328, pp. 1128. 
41

Zhu B, Lou MM, Xie GL, Zhang GQ, Zhou XP, Li B, and Jin GL. 2011. Horizontal gene 

transfer in silkworm, Bombyx mori. BMC Genomics 12, pp. 248. Retrieved from 

http://www.ncbi.nlm.nih.gov/pubmed/21595916