GM Crop Database

Database Product Description

NK603 (MON-ØØ6Ø3-6)

Host Organism: Zea mays (Maize)

Trade Name: Roundup Ready®

Trait: Glyphosate herbicide tolerance.

Trait Introduction: Microparticle bombardment of plant cells or tissue

Proposed Use: Production for human consumption and livestock feed.

Product Developer: Monsanto Company

Summary of Regulatory Approvals

Country	Food	Feed	Environment	Notes
Argentina	2004	2004	2004
Australia	2002
Brazil	2008	2008	2008
Canada	2001	2001	2001
China	2005	2005		View Approval renewed on 20 December 2007, valid until 20 December 2010.
Colombia	2004	2006	2007
El Salvador	2009	2009
European Union	2004	2004		View Authorised by decision of the EU commission on July 19th, 2004 (to be effective on October 26th, 2004).
Japan	2001	2001	2004
Korea	2002	2004
Malaysia	2010	2010
Mexico	2002	2002
New Zealand	2002
Philippines	2003	2003	2005
Russia	2008	2004
Singapore	2014
South Africa	2002	2002	2002
Taiwan	2003
Turkey		2011
United States	2000	2000	2000
Uruguay	2011	2011	2011
Vietnam	2014	2014	2014

Introduction Expand: Maize line NK603 was developed to allow the use of glyphosate containing herbicides as a weed control option for maize crops. The gene encoding a glyphosate tolerant form of the enzyme 5-enolpyruvlyshikimate-3-phosphate synthase (EPSPS) was isolated from the soil bacterium Agrobacterium tumefaciens strain CP4 and introduced into maize using recombinant DNA techniques. Glyphosate specifically binds to and inactivates EPSPS, which is involved in the biosynthesis of the aromatic amino acids tyrosine, phenylalanine and tryptophan. This enzyme is present in all plants, bacteria and fungi, but not in animals, which do not synthesize their own aromatic amino acids. Thus, EPSPS is normally present in food derived from plant and microbial sources.

For environmental release in the United States, another glyphosate tolerant maize line, GA21, was designated as the antecedent organism for NK603. Maize line NK603 and the antecedent organism GA21 were genetically engineered using the same transformation method and contain a functionally equivalent enzyme that makes the plants tolerant to the herbicide glyphosate.

Summary of Introduced Genetic Elements Expand

Code	Name	Type	Promoter, other	Terminator	Copies	Form
CP4 epsps	5-enolpyruvyl shikimate-3-phosphate synthase	HT	P-ract1/ract1 intron containing rice actin 1 promoter, transcription start site chloroplast transit peptide from A. thaliana EPSPS gene (CTP2)	A. tumefaciens nopaline synthase (nos) 3'-untranslated region	1	CP4 EPSPS gene modified for plant-preferred codons
CP4 epsps	5-enolpyruvyl shikimate-3-phosphate synthase	HT	enhanced CaMV 35S, maize HSP70 intron chloroplast transit peptide from A. thaliana EPSPS gene (CTP2)	A. tumefaciens nopaline synthase (nos) 3'-untranslated region	1	CP4 EPSPS gene modified for plant-preferred codons

Characteristics of Zea mays (Maize) Expand

Center of Origin	Reproduction	Toxins	Allergenicity
Mesoamerican region, now Mexico and Central America	Cross-pollination via wind-borne pollen is limited, pollen viability is about 30 minutes. Hybridization reported with teosinte species and rarely with members of the genus Tripsacum.	No endogenous toxins or significant levels of antinutritional factors.	Although some reported cases of maize allergy, protein(s) responsible have not been identified.

Donor Organism Characteristics Expand

Latin Name	Gene	Pathogenicity
Agrobacterium tumefaciens strain CP4	CP4 epsps	Agrobacterium tumefaciens is a common soil bacterium that is responsible for causing crown gall disease in susceptible plants. There have been no reports of adverse effects on humans or animals.

Modification Method Expand

Nutritional Data

Compositional analyses were performed on grain and forage samples of NK603 (treated with glyphosate) and the non-transformed parental control line together with a number of other commercial maize hybrids planted at trial sites in the U.S. and Europe. Analyses of grain samples included measurements of proximates (protein, fat, ash, moisture), acid detergent fibre (ADF), neutral detergent fibre (NDF), amino acids, fatty acids, vitamin E, minerals (calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, and zinc), and the antinutritional components, phytic acid and trypsin inhibitor.

In all of these tests, small statistical differences between NK603 and control lines were observed only in: six amino acids (alanine, arginine, glutamic acid, histidine, lysine, and methionine) as measured in grain from European trials (no differences were observed in material from U.S. trials); and stearic (C18:0) acid levels. Overall, these differences were not consistent across all trial sites and they were considered to reflect random variation. All compositional results were within the ranges observed for commercial non-transformed lines.

The nutritional quality of NK603 grain was assessed in feeding trials with broiler chickens, finisher swine, and laboratory rats. These studies showed that there were no differences between the transformed and non-transformed maize.

Toxicity

The CP4 EPSPS gene encodes a single polypeptide of 455 amino acids (47.6 kDa) which exhibits about 50% amino acid sequence similarity with the analogous plant EPSPS enzyme. The family of bacterial and plant EPSPS proteins are not known to display any toxic or allergenic properties. The potential toxicity of the CP4 EPSPS protein was assessed by comparing its amino acid sequence against a database of 4,677 protein sequences (not all unique) that have been associated with toxicity, and in an acute oral toxicity study in mice. The CP4 EPSPS protein did not display any sequence homology with known protein toxins and did not result in any adverse effects on test animals (50 males, 50 females) receiving doses up to 400 mg/kg of bacterially derived CP4 EPSPS protein. The single amino acid substitution within the CP4 EPSPS L214P protein did not alter the sequence comparison results.

Allergenicity

The CP4 EPSPS encoding gene was not derived from an organism known to cause allergic reactions and the allergenic potential of this protein was further evaluated by comparing its amino acid sequence against a database of known allergens, and by assessing its stability to digestion in the presence of simulated gastric fluids. There was no sequence homology between CP4 EPSPS and known allergens when checked against a database of 567 protein sequences using an 8-amino acid length window. As assessed by Western immunoblot analysis, the CP4 EPSPS was rapidly degraded (T50 < 15 sec) upon exposure to pepsin-containing simulated gastric fluid or trypsin-containing simulated intestinal fluid (T50 <= 10 min). Similar results were obtained with the variant CP4 EPSPS L214P protein.

Characteristics of the Modification Expand

The Introduced DNA
The incorporated DNA was characterized using a combination of Southern blot analyses, polymerase chain reaction (PCR) amplification of specific sequences, and nucleotide sequencing of the entire inserted fragment, including flanking sequences from the host genome. In addition, bioinformatics analyses were conducted on the inserted sequence, including host genome junction regions, to demonstrate the lack of any unforeseen, or chimeric, open reading frames (ORFs) that could potentially result in the expression of unanticipated novel proteins.

These analyses demonstrated the introduction of single copy of the transforming DNA at a single insertion site within the host genome. Some anomalies were, however, observed:

In addition to a complete copy of the introduced DNA, the insert also included a 217 bp fragment (50 bp of polylinker sequence + 167 bp of the enhancer region of the rice actin promoter) inversely linked to the 3? terminus of the introduced DNA.
Nucleotide sequencing indicated that the sequence of the CP4 EPSPS gene within the second (3? proximal) cassette differed by two nucleotides from the inserted sequence. This gave rise to a single amino acid substitution at position 214 of the expressed protein (leucine --> proline; variant protein referred to as: CP4 EPSPS L214P).
Analyses of specific PCR products from the 3? terminus of the inserted DNA revealed that an additional segment comprising 305 bp of chloroplast DNA had been co-integrated. Bioinformatics analysis indicated that this sequence corresponded to a portion of the maize DNA-directed RNA polymerase alpha-subunit and ribosomal S11 protein. The source of this DNA was believed to be the chloroplast of the transformed cell.

Genetic Stability of the Introduced Trait
Southern blot analyses of genomic DNA isolated from plants over six generations of crossing and three generations of self-pollination were used to confirm that the introduced DNA was stably inherited and segregated as a single locus according to Mendelian genetics. Multigenerational stable expression of the glyphosate tolerant trait was demonstrated using bioassay (tolerance to glyphosate application) and enzyme linked immunosorbent assay (ELISA) to measure CP4 EPSPS protein concentration.

Expressed Material
Expression of full-length (approx. 47 kDa) CP4 EPSPS protein was confirmed by Western immunoblot analysis and protein concentrations were estimated using ELISA. Plant samples from line NK603 and the non-transformed parental control line were collected from six non-replicated and two replicated field sites during the 1998 growing season and assayed using a double antibody sandwich (DAS)-ELISA employing monoclonal anti-CP4 EPSPS antibody as the capture antibody and a horseradish peroxidase-conjugated anti-CP4 EPSPS polyclonal antibody as the detection reagent. Mean CP4 EPSPS protein levels (across all sites) were 25.6 ?/g (fwt; range 18.0 ? 31.2) and 10.9 ?/g (fwt; range 6.9 ? 15.6) for forage and grain tissue, respectively.

Environmental Safety Considerations Expand

Outcrossing
Pollen production and viability were unchanged in line NK603 and, therefore, pollen dispersal by wind and outcrossing frequency should be no different than for other maize varieties. Gene exchange between NK603 and other cultivated maize varieties will be similar to that which occurs naturally between cultivated maize varieties at the present time. In Canada and the United States, where there are few plant species closely-related to maize in the wild, the risk of gene flow to other species is remote. Cultivated maize, Zea mays L. subsp. mays, is sexually compatible with other members of the genus Zea, and to a much lesser degree with members of the genus Tripsacum. None of the sexually compatible relatives of maize in Canada or the United States are considered to be weeds in these countries and it is therefore unlikely that introgression of the CP4 EPSPS gene would provide a selective advantage to these populations as they would not be routinely subject to herbicide treatments.

Weediness Potential
No competitive advantage was conferred to NK603, other than that conferred by resistance to glyphosate herbicide. Resistance to glyphosate containing herbicides will not, in itself, render maize weedy or invasive of natural habitats since none of the reproductive or growth characteristics were modified.
Cultivated maize is unlikely to establish in non-cropped habitats and there have been no reports of maize surviving as a weed. In agriculture, maize volunteers are not uncommon but are easily controlled by mechanical means or by using herbicides that are not based on glyphosate as appropriate. Zea mays is not invasive and is a weak competitor with very limited seed dispersal.

Secondary and Non-Target Adverse Effects
No environmentally toxic components were detected in NK603. CP4 EPSPS protein is not a known toxin and analogous proteins are found in all plants and microorganisms. There are no anticipated adverse effects of NK603 on non-target organisms that would be different from conventional maize varieties.

Impact on Biodiversity
Maize line NK603 has no novel phenotypic characteristics that would extend its use beyond the current geographic range of maize production. Since the risk of outcrossing with wild relatives in Canada and the United States is remote, it was determined that the risk of transferring genetic traits from NK603 to species in unmanaged environments was not a significant concern.

Other Considerations
Consideration was made as to whether the introduction of crops tolerant to glyphosate would result in a significant increase in the use of the herbicide, and lead to the evolution of glyphosate resistant weeds. It was determined that the risk of increasing the selection of glyphosate tolerant weeds was low and could be mitigated through the use of other approved herbicides with a mode of action dissimilar to glyphosate.

Food and/or Feed Safety Considerations Expand: Nutritional Data
Compositional analyses were performed on grain and forage samples of NK603 (treated with glyphosate) and the non-transformed parental control line together with a number of other commercial maize hybrids planted at trial sites in the U.S. and Europe. Analyses of grain samples included measurements of proximates (protein, fat, ash, moisture), acid detergent fibre (ADF), neutral detergent fibre (NDF), amino acids, fatty acids, vitamin E, minerals (calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, and zinc), and the antinutritional components, phytic acid and trypsin inhibitor.

In all of these tests, small statistical differences between NK603 and control lines were observed only in: six amino acids (alanine, arginine, glutamic acid, histidine, lysine, and methionine) as measured in grain from European trials (no differences were observed in material from U.S. trials); and stearic (C18:0) acid levels. Overall, these differences were not consistent across all trial sites and they were considered to reflect random variation. All compositional results were within the ranges observed for commercial non-transformed lines.

The nutritional quality of NK603 grain was assessed in feeding trials with broiler chickens, finisher swine, and laboratory rats. These studies showed that there were no differences between the transformed and non-transformed maize.

Toxicity
The CP4 EPSPS gene encodes a single polypeptide of 455 amino acids (47.6 kDa) which exhibits about 50% amino acid sequence similarity with the analogous plant EPSPS enzyme. The family of bacterial and plant EPSPS proteins are not known to display any toxic or allergenic properties. The potential toxicity of the CP4 EPSPS protein was assessed by comparing its amino acid sequence against a database of 4,677 protein sequences (not all unique) that have been associated with toxicity, and in an acute oral toxicity study in mice. The CP4 EPSPS protein did not display any sequence homology with known protein toxins and did not result in any adverse effects on test animals (50 males, 50 females) receiving doses up to 400 mg/kg of bacterially derived CP4 EPSPS protein. The single amino acid substitution within the CP4 EPSPS L214P protein did not alter the sequence comparison results.

Allergenicity
The CP4 EPSPS encoding gene was not derived from an organism known to cause allergic reactions and the allergenic potential of this protein was further evaluated by comparing its amino acid sequence against a database of known allergens, and by assessing its stability to digestion in the presence of simulated gastric fluids. There was no sequence homology between CP4 EPSPS and known allergens when checked against a database of 567 protein sequences using an 8-amino acid length window. As assessed by Western immunoblot analysis, the CP4 EPSPS was rapidly degraded (T50 < 15 sec) upon exposure to pepsin-containing simulated gastric fluid or trypsin-containing simulated intestinal fluid (T50 <= 10 min). Similar results were obtained with the variant CP4 EPSPS L214P protein.

Links to Further Information Expand

Australia New Zealand Food Authority

Final risk assessment report: glyphosate-tolerant corn line NK603
[PDF Size: 425.38K bytes]

Canadian Food Inspection Agency, Plant Biosafety Office

Decision Document DD2002-35 Determination of the Safety of Monsanto Canada Inc.’s Roundup ReadyTM Corn (Zea mays L.) Line 603
[PDF Size: 37.13K bytes]

Comissão Técnica Nacional de Biossegurança - CTNBio (Brazil)

Risk Assessment of Herbicide Tolerant Maize (NK603)
[PDF Size: 487.58K bytes]

European Commission

COMMISSION DECISION of 3 March 2005 authorising the placing on the market of foods and food ingredients derived from genetically modified maize line NK 603 as novel foods or novel food ingredients under Regulation (EC) No 258/97 of the European Parliament and of the Council
[PDF Size: 44.27K bytes]

European Commission: Community Register of GM Food and Feed

Notification of the placing on the Community Register of MON-ØØ6Ø3-6.
[PDF Size: 11.49K bytes]

European Food Safety Authority

Opinion of the Scientific Panel on Genetically Modified Organisms on a request from the Commission related to the safety of foods and food ingredients derived from herbicide-tolerant genetically modified maize NK603, for which a request for placing on the market was submitted under Article 4 of the Novel Food Regulation (EC) No 258/97 by Monsanto (QUESTION NO EFSA-Q-2003-002). Opinion adopted on 25 November 2003
[PDF Size: 181.57K bytes]

Health Canada, Office of Food Biotechnology

Novel food decision summary for glyphosate-tolerant maize line NK603
[PDF Size: 15.13K bytes]

Japanese Biosafety Clearing House, Ministry of Environment

Outline of the biological diversity risk assessment report: Type 1 use approval for NK603
[PDF Size: 130.40K bytes]

Monsanto Company

Product safety description
[PDF Size: 275.70K bytes]

Philippines Department of Agriculture, Bureau of Plant Industry

Determination of the Safety of Monsanto’s Corn NK 603 (Glyphosate-Tolerant Corn) for Direct Use as Food, Feed and for Processing and for Propagation
[PDF Size: 30.90K bytes]

U.S.Department of Agriculture, Animal and Plant Health Inspection Service

Monsanto Co. Request for Extension of Determination of Nonregulated Status to the Additional Regulated Article: Roundup Ready Corn Line NK603
[PDF Size: 4.47M bytes]

US Food and Drug Administration

Letter to Monsanto regarding NK603
[PDF Size: 84.06K bytes]
Memorandum to file concerning glyphosate-tolerant maize link NK603.
[PDF Size: 376.82K bytes]

This record was last modified on Friday, October 28, 2016

Product Related Info

Biology Documents

Maize biology document
Biology of Maize L.
General Description

Maize is a tall, monoecious, annual grass varying in height from 1 to 4 meters (Watson & Dallwitz 1992). The main stem is made up of clearly defined nodes and internodes. Internodes are wide at the base and gradually taper to the terminal inflorescence at the top of the plant. Leaf blades are found in an alternating pattern along the stem. Maize is a unique grass as both male and female flowers are borne on the same plant but are located separately. The tassels or staminate (male) inflorescence form large spreading terminal panicles that resemble spike-like racemes. Pollen is shed from the tassel and is viable for approximately 10 to 30 minutes as it is rapidly desiccated in the air (Kiesselbach 1980). Maize plants shed pollen for up to 14 days. The reproductive phase begins when one or two auxiliary buds, present in the leaf axils, develop and form the pistillate inflorescence or female flower (Purseglove 1972). The auxiliary bud starts the transformation to form a long ‘cob’ on which the flowers will be borne. From each flower a style begins to elongate towards the tip of the cob in preparation for fertilization. These styles form long threads, known as silks. The base of the silk is unique, as it elongates continuously until fertilization occurs (Purseglove 1972). Styles may reach a length of 30 cm, the longest known in the plant kingdom. Individual maize kernels, or fruit, are unique in that mature seed is not covered by floral bracts (glumes, lemmas, and paleas) as in most other grasses, but rather the entire structure is enclosed and protected by large modified leaf bracts, collectively referred to as the ear (Hitchcock and Chase 1951). The mature female flowers will remain ready for fertilization for up to two weeks, at which point if fertilization has not occurred, the nucleus will de-organize and fertilization will no longer be possible (Hitchcock & Chase 1951). The pollen of maize, a protandrous plant, matures before the female flower is receptive (Purseglove 1972). This may have been an ancient mechanism to ensure cross-pollination, but is no longer considered conducive to modern agricultural practices. However, decades of conventional selection and improvement have produced many maize varieties with similar maturities for both male and female flowers, to ensure seed set for agricultural proposes.

Reproduction

Under natural conditions, maize reproduces only by seed production. Pollination occurs with the transfer of pollen from the tassels to the silks of the ear. About 95% of the ovules are cross-pollinated and about 5% are self-pollinated (Poehlman 1959), although plants are completely self-compatible. Maize, as a thoroughly domesticated plant, has lost all ability to disseminate its seeds and relies entirely on the aid of man for its distribution (Stoskopf 1985). The kernels are tightly held on the cobs and if ears fall to the ground, so many competing seedlings emerge that the likelihood that any will grow to maturity is extremely low. Maize cannot reproduce asexually by natural means. It is possible to reproduce maize using tissue culture techniques, however, it has proven extremely difficult with a low rate of success (Hoisington et al. 1998).

Classification and Phylogeny of Maize

Zea is a genus belonging to the grass family, Poaceae, in the Andropogoneae tribe, but is commonly cited in literature to belong to the tribe Maydeae. Zea (zeia) was derived from an old Greek name for a food grass. The genus Zea consists of four species of which only Zea mays ssp. mays L. is economically important. The other Zea species, referred to as teosintes, are largely wild grasses native to Mexico and Central America (Doebley 1990). The number of chromosomes in Zea mays is 2n=20, 21, 22, 24 (FAO 2000c). The tribe Maydeae consists of seven genera: two of American origin, Zea and Tripsacum; and five of Eastern origin which extend from India through Southeastern Asia to Australia and include Coix, Sclerachne, Polytoca, Chionachne and Trilobachne (Watson & Dallwitz 1992). It is generally agreed that maize phylogeny was largely determined by the American genera Zea and Tripsacum, however it is accepted that the genus Coix contributed to the phylogenetic development of the species Z. mays (Radu et al. 1997). The genus Manisuris, from the tribe Andropogoneae, may also have contributed to the evolution of Zea mays (Eubanks 1997a; Radu et al. 1997).

Center of Origin and Progenitors of Maize

The center of origin for Zea mays ssp. mays has been established as the Mesoamerican region, now Mexico and Central America (Watson & Dallwitz 1992). The exact period of domestication and the ancestors from which maize arose are unclear. Archaeological records suggest that domestication of maize began at least 6000 years ago, occurring independently in regions of the southwestern United States, Mexico, and Central America (Mangelsdorf 1974). The origins of domesticated maize have been difficult to trace as hybridization events in its evolution are thought to have involved a now extinct wild maize ancestor of which little evidence has been found (Eubanks 1997a).

Germplasm Diversity

A study in 1992 concluded that maize landraces occupied 42% of the land under production in less developed countries (México 1994). Mexico and Central America are the only regions where ancient maize lines, such as pod corn, are found (Mink & Dorosh 1985). The survival of maize landraces has been attributed to the integral role maize sustains in small communities where it has very specific uses for food and other special functions. These landraces have been well characterized in Latin America, and germplasm not yet evaluated is known to be present in the region. There is a growing trend in developing countries to adopt improved maize varieties, primarily to meet market demand. In Mexico, only 20% of the corn varieties grown 50 years ago remain in cultivation (World Watch Institute 2000). The narrowing of genetic diversity in modern maize varieties emphasizes the importance of conserving genetic traits for future plant breeding. Leading the way in preserving maize germplasm is CIMMYT (International Maize and Wheat Improvement Centre), which has the world’s largest collection of maize accessions, with over 17,000 lines (CIMMYT 2000). Collections of distant maize relatives native to Asia have been recommended by conservation experts to ensure their preservation for future research (Sharma 1998).

Relatives of Maize

The closest wild relatives of maize are the teosintes which all belong to the genus Zea. The teosintes are wild grasses native to Mexico and Central America and have limited distribution (Mangelsdorf et al. 1981). Teosinte species show little tendency to spread beyond their natural range and distribution is restricted to North, Central and South America (Watson & Dallwitz 1992). The nearest teosinte relative to Z. mays ssp. mays is Z. mays ssp. mexicana (Schrader) Iltis (previously classified as Euchlaena mexicana, Zea mexicana) (2n = 20). This Central Mexican annual teosinte is a large flowered, mostly weedy grass with a broad distribution across the central highlands of Mexico. It does not spread readily. It has limited use as a forage and green fodder crop, but can be problematic due to weedy tendencies (Doebley 1990, Watson & Dallwitz 1992). The closest wild relatives to maize outside the Zea genus are from the genus Tripsacum. The genus Tripsacum is comprised of about 12 species that are mostly native to Mexico and Guatemala but are widely distributed throughout warm regions in the USA and South America, with some species present in Asia and Southeast Asia (Watson & Dallwitz 1992). All species are perennial, warm season grasses.

Outcrossing

Gene flow from maize can occur by two means: pollen transfer and seed dispersal. Seed dispersal can be readily controlled in maize as domestication has all but eliminated any seed dispersal mechanisms that ancestral maize may have previously used (Purseglove 1972). The kernels are held tightly on the cobs and if the ear falls to the ground, competing seedlings limit growth to maturity (Gould 1968). Pollen movement is the only effective means of gene escape from maize plants. Pollen is released from the tassels at the top of the plant and transported by wind to the female flowers located on the stalk. Pollen shed occurs over a 14 day period, with a peak during the first 5 days of shed (Sears 2000). The stigmas are receptive for a large part of this two week interval (Kiesselbach 1980). Insects, such as bees, have been observed to collect pollen from maize tassels, but they do not play a significant role in cross-pollination as there is no incentive to visit the female flowers (Rayor et al. 1972).

Wind speed and direction affect pollen distribution

Differences in flowering dates among commercial maize varieties are small. Cross-pollination between varieties may occur if grown in adjacent fields. The limited viability of maize pollen reduces the risk of cross-pollination, as a receptive host must be found within the 30 minutes that the pollen remains biologically active. Cross-pollination is also affected by the concentration of maize pollen released; pollen produced by a maize crop will successfully compete with foreign pollen sources when present in higher concentrations (Rayor et al. 1972). The isolation of crops using separation distances and physical barriers are common techniques for restricting gene flow and ensuring seed purity for maize seed production. Cross-pollination is controlled in seed lots by separating different lines. The OECD standards require a minimum 200 m (660 ft) isolation distance for maize seed production. This distance has been estimated to maintain inbred lines at 99.9% purity. Physical barriers, such as trees or barrier rows, are also effective in reducing cross-pollination. Detasseling or bagging the tassel effectively prevents pollen movement and limits gene flow.

Intraspecific hybidization

All forms of Zea mays spp mays, such as dent, sweet, and pop corn, freely cross pollinate forming fertile hybrids (Pursglove 1972).

Interspecific hybridization

All teosintes can be crossed to maize and form fertile hybrids, except for the tetraploid Z. perennis. Maize-teosinte hybrids exhibit low fitness and have little impact on gene introgression in subsequent generations (Galinat 1988). The tendency to form natural hybrids differs among teosintes: Z. luxurians rarely hybridizes with maize, whereas Z. mays ssp. mexicana frequently forms hybrids (Wilkes 1977). Molecular data confirms that there is gene flow between maize and teosinte and suggests that introgression of maize and teosinte occurs in both directions but at low levels (Doebley 1990).

Intergeneric hybridization Tripsacum species (T. dactyloides, T. floridanum, T. lanceolatum, and T. pilosum) have been successfully hand crossed with maize to form hybrids. The hybrids generally have 28 chromosomes, 10 from maize and 18 from Tripsacum, and are pollen sterile with limited female fertility (Mangelsdorf & Reeves 1939, Mangelsdorf 1974). This infertility is common in such wide crosses because of differences in chromosome number and lack of pairing between chromosomes (Eubanks 1997b). Maize readily crosses with hexaploid wheat (Triticum aestivum) with high frequencies of fertilization and embryo formation (plant breeders use maize pollen to develop double haploids of hexaploid wheat). However, maize chromosomes are eliminated from the genome during the initial stages of meiosis and result in haploid embryos. There is little evidence to suggest fertile hybrids between maize and hexaploid wheat could be produced in nature. There have been unsubstantiated reports of hybridization between maize and sugar cane (Saccaharum sp.).

Biology References
1. CIMMYT (International Maize and Wheat Improvement Centre) (2000). CGIAR Research, Areas of Research: Maize (Zea mays L.) http://www.cgiar.org/areas/maize.htm
2. Doebley, J. F. (1990). Molecular Evidence for Gene Flow among Zea species. BioScience 40, 443- 448.
3. Eubanks, M.W. (1997a). Further evidence for two progenitors in the origin of maize. Maize Newsletter 71, 35-35.
4. FAO (2000c). Species Description. Zea mays L. http://www.fao.org/WAICENT/faoinfo/agricult/agp/agpc/doc/gbase/data/pf000342.htm
5. Galinat, W.C. (1988). The origin of corn. In: Corn and Corn Improvement. Agronomy Monographs No.18. American Society of Agronomy, G.F Sprague and J.W. Dudley, (eds.). Madison, Wisconsin, pp. 1-31.
6. Gould, F.W. (1968). Grass Systematics. McGraw Hill, N.Y., USA.
7. Hitchcock, A.S. & A. Chase. (1951). Manual of the Grasses of the United States (Volume 2). Dover Publications: N.Y. p. 790-796.
8. Hoisington, D., Listman, G.M. & Morris, M.L. (1998). Varietal development: applied biotechnology. In: Maize Seed Industries in Developing Countries. M. L. Morris (ed). Lynne Rienner Publishers, Inc. pp. 77-102.
9. Kiesselbach, T.A. (1980). The structure and reproduction of corn. Reprint of: Research Bulletin No. 161. 1949. Agricultural Experiment Station, Lincoln, Nebraska. University of Nebraska Press. p. 93.
10. Laurie, D.A. & Bennett, M.D. (1986). Wheat x maize hybridization. Can. J. Genet. Cytol. 28, 313-316.
11. Mangelsdorf, P. C. & Reeves, R.G. (1939). The origin of Indian corn and its relatives. Texas Agric. Expt. Sta. Bull. 574.
12. Mangelsdorf, P. C. (1974). Corn: its Origin, Evolution and Improvement. Harvard Univ. Press, Cambridge, Mass.
13. Mangelsdorf, P. C., Roberts, L.M. & Rogers, J.S. (1981). The probable origin of annual teosintes. Bussey Inst., Harvard Univ. Publ. 10, 1- 69.
14. México, D.F. (1994). Maize seed industries revisited: emerging roles of the public and private sectors. World Maize Facts and Trends1993/94. CIMMYT.
15. Mink, S. D. & Dorosh, P.A. (1987). An overview of corn production. In: The Corn Economy of Indonesia. Cornell University Press, London.
16. Poehlman, J.M. (1959). Breeding Field Crops. Holt, New York, USA.
17. Purseglove, J.W. (1972). Tropical Crops: Monocotyledons 1. Longman Group Limited., London.
18. Radu, A, Urechean, V., Naidin, C. & Motorga, V. (1997). The theoretical significance of a mutant in the phylogeny of the species Zea mays L. Maize Newsletter 71, 77-78.
19. Rayor, G.S., Ogden, E.C. & Hayes, J.V. (1972). Dispersion and deposition of corn pollen from experimental sources. Agronomy Journal 64, 420-427.
20. Sears, M.K., Stanley-Horn, D.E. & Matilla, H.R. (2000). Ecological impact of Bt corn pollen on Monarch butterfly in Ontario. Canadian Food Inspection Agency (http://www.cfia-acia.agr.ca/english/ plaveg/pbo/btmone.shtml)
21. Sharma, A.B. (1998). Experts for conservation of wild crop varieties. The Financial Express. Indian Express Group.
22. Stoskopf, N.C. (1985). Cereal Grain Crops. Reston, Virginia: Reston Publishing Company, Inc., Prentice-Hall Company.
23. Watson, L. & Dallwitz, M.J. (1992). Grass Genera of the World: Descriptions, Illustrations, Identification, and Information Retrieval; including Synonyms, Morphology, Anatomy, Physiology, Phytochemistry, Cytology, Classification, Pathogens, World and Local Distribution, and References. Version:18th August 1999. http://biodiversity.uno.edu/delta
24. World Watch Institute (2000). Crop gene diversity declining. Trends in Plant Science 5, 7.
25. Wilkes, H.G. (1977). Hybridization of maize and teosinte, in Mexico and Guatemala and the improvement of maize. Economic Botany 31, 254-293.
LAST UPDATED: SEPTEMBER 2002

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Introduction Expand

Summary of Introduced Genetic Elements Expand

Characteristics of Zea mays (Maize) Expand

Donor Organism Characteristics Expand

Modification Method Expand

Characteristics of the Modification Expand

Environmental Safety Considerations Expand

Food and/or Feed Safety Considerations Expand

Links to Further Information Expand

Output Options

Synopsis

Product Related Info

Query Options

Help

GM Crop Database

Database Product Description

Summary of Regulatory Approvals

Introduction Expand

Summary of Introduced Genetic Elements Expand

Characteristics of Zea mays (Maize) Expand

Donor Organism Characteristics Expand

Modification Method Expand

Characteristics of the Modification Expand

Environmental Safety Considerations Expand

Food and/or Feed Safety Considerations Expand

Links to Further Information Expand

Output Options

Synopsis

Product Related Info

Biology Documents

Biology of Maize L.

Documents

Detection

Figures

Query Options

Help