Field Testing
The maize event T25 has been field tested in the major maize growing regions of the United States since 1992 and in Canada since 1993. T25 has been evaluated extensively in the laboratory, greenhouse, and field experiments. Field reports on T25, compared to non-transgenic counterparts, determined that agronomic characteristics such as yield, plant height, over-wintering capacity, flowering period, and disease susceptibility were within the normal range of expression currently displayed by commercial maize hybrids. Overall the field data reports and data on agronomic traits showed that maize event T25 and lines derived from these event, have no potential to pose a plant pest risk.
Outcrossing
Since pollen production and viability were unchanged by the genetic modification resulting in maize line T25, pollen dispersal by wind and outcrossing frequency should be no different than for other maize varieties. Gene exchange between maize lines of T25 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 appears 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.
Weediness Potential
No competitive advantage was conferred to maize line T25, other than that conferred by resistance to glufosinate ammonium herbicides. Resistance to glufosinate ammonium 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, other than glufosinate ammonium. Zea mays is not invasive and is a weak competitor with very limited seed dispersal.
Secondary and Non-Target Adverse Effects
It was determined that because genetically modified maize event T25 did not have a significant adverse impact on organisms beneficial to plants or agriculture or on nontarget organisms, this events was not expected to impact threatened or endangered species. The PAT enzyme responsible for glufosinate ammonium tolerance has very specific enzymatic activity, does not possess proteolytic or heat stability typical of toxic compounds, and does not affect the metabolism of the plant. Other crops such as sugarbeet, oilseed rape, chicory, soybean, cotton and rice, have been modified by recombinant DNA techniques to express the PAT enzyme with no apparent effect on the agronomic performance of succeeding crops. The expression level of PAT in T25 is comparable to other transformed species, and therefore it was concluded that no significant residual effects from T25 is expected.
Impact on Biodiversity
T25 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 T25 maize lines to species in unmanaged environments was insignificant. It was determined that the overall relative impact on plant biodiversity was neutral, as was the impact on animal and microbe biodiversity since the introduced PAT enzyme was not expected to alter the plant's metabolism and as such, novel compounds would not be produced.
