Field Trial Evaluations
Agronomic data were collected in a series of three experiments (A, B, and C) from confined field trials of 98140 and non-transgenic control maize conducted at up to 15 locations in 2006. The trial locations provided a range of environmental and agronomic conditions representative of the major corn growing regions in the U.S. and Canada, where commercial production of event 98140 is expected. Agronomic practices used to prepare and maintain each field site were characteristic of each respective region.
Experiment A: Comprised seven locations in the major corn growing regions of the Midwest during the 2006 growing season and measured the following parameters: time to silking, time to pollen shed, plant height, ear height, final population, percent moisture, test weight and yield. For all characteristics measured, no statistical differences in mean values were seen between 98140 and control maize across locations (adjusted P-value > 0.05).
Experiment B: Comprised nine locations in the major corn growing region of North America during the 2006 growing season and measured the following parameters: early population, final population, seedling vigor, time to silking, time to pollen shed, stalk lodging, root lodging, stay green, disease incidence, insect damage, yield, plant height and ear height. For all characteristics measured, no statistical differences in mean values were seen between 98140 and control maize across locations (adjusted P-value > 0.05).
Experiment C: Comprised six locations in the major corn growing regions of North America during the 2006 growing season and measured the following parameters: early population, final population, seedling vigor, time to silking, time to pollen shed, stalk lodging, root lodging, stay green, disease incidence, insect damage, plant height, ear height and pollen viability (shape & color) over time. For all characteristics measured, no statistical differences in mean values were seen between 98140 and control maize across locations (adjusted P-value > 0.05).
Ecological Observations
Ecological observations (plant interactions with insects and diseases) were recorded for all USDA-APHIS permitted field trials of 98140 maize during the 2005 and 2006 growing seasons. Plant breeders and field staff familiar with plant pathology and entomology observed event 98140 and control lines at least every four weeks for insect and disease pressure and recorded the severity of any stressor seen. In every case, the severity of insect or disease stress on event 98140 was not qualitatively different from various control lines growing at the same location. These results support the conclusion that the ecological interactions for event 98140 were comparable to control maize lines with similar genetics or to conventional maize lines.
Weediness Potential
Commercial maize varieties are not effective in invading established ecosystems (CFIA, 1994). Maize hybrids have been domesticated for such a long period of time that the seeds cannot be disseminated without human intervention, nor can corn seed readily survive in the U.S. and Canadian environments from one growing season to the next because of the poor dormancy. Any volunteer corn plants are easily identified and controlled through manual or chemical means.
There is little probability that event 98140 maize could become a problem weed. Various characteristics that might impart weediness potential were evaluated for 98140 and control maize in comparative studies, and no differences were seen in characteristics such as seed germination, emergence, seedling vigor, yield, and disease/insect susceptibility. Assessment of these data detected no biologically significant differences between event 98140 and control maize indicative of a selective advantage that would result in increased weediness potential. Furthermore, postharvest monitoring of field trial plots containing 98140 maize have shown no differences in survivability or persistence of event 98140 as compared to conventional maize.
Outcrossing
Maize is an open pollinated monoecious plant that produces abundant pollen. Maize pollen is among the largest and heaviest of the wind-dispersed pollen grains, thus limiting the distance it can travel. The potential transfer of traits in pollen to other corn plants is sometimes called pollen-mediated gene flow. There are many factors that affect pollen-mediated gene flow in maize including isolation distance between pollen source and recipient field, size of pollen source and recipient field, shape and orientation of pollen source and recipient field, wind direction and velocity, rain, temperature and humidity, pollen viability, silk receptivity, synchrony of flowering between source and recipient fields, pollen competition and physical barriers. Event 98140 is unchanged with respect to pollen characteristics.
Maize freely hybridizes with annual teosinte (Zea mays ssp. Mexicana) when in close proximity. These wild maize relatives are native to Central America and are not present in the United States or Canada, except for special plantings. Tripsacum, another genus related to Zea, contains sixteen species, of which twelve are native to Mexico and Guatemala. Three species of Tripsacum have been reported in the continental United States: T. dactyloides, T. floridanum and T. lanceolatum. Of these, T. dactyloides, Eastern Gama Grass, is the only species of widespread occurrence and of any agricultural importance. It is commonly grown as a forage grass and has been the subject of some agronomic improvement (i.e., selection and classical breeding). T. floridanum is known from southern Florida and T. lanceolatum is present in the Mule Mountains of Arizona and possibly southern New Mexico. Even though some Tripsacum species occur in areas where maize is cultivated, gene introgression from maize under natural conditions is highly unlikely, if not impossible. Hybrids of Tripsacum species with Zea mays are difficult to obtain outside of the controlled conditions of laboratory and greenhouse. Seed obtained from such crosses are often sterile or progeny have greatly reduced fertility.
Potential Impact on Farming Practices
Cultivation and Management Practices: No negative impact is expected from the introduction of 98140 maize on current cultivation and management practices for maize. Event 98140 has been shown to be comparable to conventional maize in phenotypic, ecological and compositional characteristics. Event 98140 maize is expected to be similar in its agronomic characteristics and have the same levels of resistance to insects and diseases as other commercially available maize.
Weed Control: The commercialization of herbicide tolerant 98140 maize is expected to have a beneficial impact on weed control practices, as growers will have more herbicide options available to address their regional weed problems. Event 98140 maize will enable growers to choose an optimal combination of glyphosate, ALS-inhibiting herbicides, and other complementary herbicides to best manage their individual weed populations. Growers value the glyphosate-resistant crop trait and the utility of glyphosate. The availability of event 98140 maize will enable growers to proactively manage weed populations while delaying population shifts to troublesome weeds or the evolution of resistant weeds. Alternating herbicides with different modes of actions to control weeds generally is recommended to help delay the evolution of herbicide-resistant weeds. Therefore, incorporating tolerance to two herbicides with different modes of action in maize, as in event 98140, will be useful.
Potential Impact on Biodiversity
Event 98140 maize does not have an increased weediness potential, and unconfined cultivation of 98140 maize hybrids should not lead to increased weediness of other sexually compatible relatives, as non cultivated Zea mays species are not found in the United States or Canada. Therefore, it is unlikely to have effects on non-target organisms common to the agricultural ecosystem or threatened or endangered species, and there is no apparent potential for significant impact to biodiversity.
