The frequency of pollen flow with distance in corn is demonstrated and explained well in this report on GE and non-GE hybrids grown in close proximity at three locations over three years. The simple dominance of the yellow colored GE kernels shows the relationship visually:
B. L. Ma, February, 2005
Cross fertilization and concerns over cross contamination
Corn (Zea mays L.), also called maize, is a monoecious crop with male (staminate inflorescence) and female (pistillate inflorescence) flowers formed in separate parts of the same plant, leading to a high degree of cross-pollination between plants. It is reported that cultivated corn freely crosses with nearly all members of the genus, including several hundred mutants1. The male inflorescence (tassel) of corn can produce considerably more pollen grains than are required for pollination of a single plant. Westgate et al.2 estimated that individual tassels produced 4.5 x 106 pollen grains, and pollen shedding often lasts 5 or 6 days.
Interest in pollen movement has increased recently due to possible contamination of conventional crops from pollen of genetically engineered (GE) genotypes. Under natural conditions, pollen can travel from field to field, but the majority of pollen grains are assumed to fall within the row space, as corn pollen is one of the heaviest and largest (about 90-100 µm in diameter) among wind-dispersed pollen grains1,4. For corn producers, the major issue is that contamination of conventional hybrids by pollen from neighboring GE hybrids will restrict marketing the grain harvested from the contaminated field. Such grain is declared as essentially transgenic and will only be accepted by specific elevators and processors3. Thus, there is an urgent need to understand pollen-mediated gene flow and the minimum distance required to isolate conventional hybrids from neighboring GE cornfields.
The endosperm of corn kernels can be yellow or white, with yellow dominant to white. These colors are easily observable and can be used as markers in studies designed to measure cross-fertilization. It is possible to quantify the extent of out-crossing between genotypes by planting a white-kernel hybrid next to a yellow hybrid and measuring the incidence of yellow kernels on white cobs. Using this production system, we determined: i) the frequency of cross-fertilization of a corn genotype by foreign pollen of neighboring hybrids; and ii) the practical distance from neighboring GE corn fields required to grow non-GE corn. Read the full article: FREQUENCY OF POLLEN DRIFT IN GENETICALLY ENGINEERED CORN
Suggested Reading: Methods to Enable the Coexistence of Diverse Corn Production Systems