AgDM Special Feature newsletter article, April 2000

Frequently asked questions regarding the production of transgenic crops

The transgenic crop, also known as genetically modified organism (GMO), debate has created many new issues for production agriculture. Most are not unique to transgenic crops, they are just the beginning of differentiated markets based on a wide range of new traits.

The Iowa Grain Quality Initiative has assembled this question/answer checklist to help you with planting decisions. Look for more updates and information throughout the 2000 season.

Production Questions

by Dale Farnham, Former Assistant Professor of Agronomy

I plan to plant only conventional hybrids and varieties on my farm; however, my neighbor plants a mix of conventional and transgenic crops . What is the potential for cross-pollination between my neighbor's crops and mine?

If the crop in question is soybean, it's a fairly safe bet that there will be no cross-pollination. The soybean plant produces a perfect flower (each flower contains both male and female reproductive structures) and is selfpollinated. There is little chance of cross-pollination in soybean.

If the crop in question is corn, chances for crosspollination increase considerably (the corn plant is largely self-pollinated, also, however a certain degree of cross-pollination is common in all corn fields). The corn plant produces separate flowers for the male and female reproductive structures (male flower, or tassel, at the top of the plant and the female flower, or ear, located midway up the stalk). An average corn plant will produce between two million and five million pollen grains. An average ear will produce 750 to 1,000 ovules (and silks). That means that there are approximately 2,000 to 5,000 pollen grains produced for each silk.

Pollen is shed from the tassel and falls onto the silks of the ear, a distance of approximately three to five feet. Obviously, not all of the pollen will fall directly onto an awaiting silk. Some of the pollen will be picked up and transported by the wind and may pollinate silks on neighboring plants, some will fall onto the leaves, some will be picked up and carried away by insects or birds, and some will fall onto the ground. The distance that pollen can be carried on the wind is the real question.

How far will pollen travel on the wind?

Past studies have shown that the bulk of a corn plant's pollen will fall within a 20-foot radius of the plant. However, some may be carried much farther, perhaps up to a quarter of a mile or farther.

It is important to remember, however, that pollen shed is not a continuous process. It turns on and off in response to the environmental conditions at the time. Thus, very little, if any, pollen is being shed on rainy days, on windy days, on extremely hot days, or on extremely cool days. In addition, the average life of a pollen grain is only about 20 minutes, so it needs to do its work quickly before it loses its viability.

What would be an appropriate separation distance between the conventional and transgenic crops to avoid potential cross-pollination?

The seed industry uses a separation distance of 660 feet (40 rods) for seed fields by convention. There is nothing magical about this distance, however. Obviously, the greater the distance, the less likely the chance for crosspollination.

What appropriate steps should be taken to reduce the chances of cross-pollination from neighboring fields?

Begin by talking with your neighbor(s). Find out what hybrids are intended to be planted in each field and design a layout that will reduce the possibility of cross-pollination. Also, consider how each field lies with regard to the prevailing winds.

Appropriate buffer strips (non-transgenic corn hybrid or an alternate crop such as soybean or forage) may need to be factored into the field layout. At harvest time, rows directly adjacent to the neighbor's field may need to be harvested separately and marketed or used differently, perhaps fed onfarm or sold to a local feed mill.

Are there other preventive measures that may help reduce the chances of contamination or cross-pollination?

Contamination can occur at any of a variety of points throughout the production and marketing channels, from the seed provider to the end-user. Thus, cleanliness and identity preservation will be critical factors in keeping contamination to a minimum.

To begin, prepare field plans and designate where specific transgenic and non-transgenic crops will be grown. Draw detailed field maps that show the location of each hybrid or variety. Design the plan so all transgenic hybrids or varieties are planted either first or last, thus reducing the amount of time necessary to clean out the planter.

Take the time to adequately clean the seed hoppers and metering mechanisms of the planter. A single kernel of corn seed that is left in the planter has the potential of producing several thousand kernels of unwanted, contaminated grain. Retain tags from seed bags for each hybrid or variety planted. At harvest time, harvest transgenic and nontransgenic crops in the same manner in which they were planted - one at a time - to reduce the amount of time required to clean the combine and transporting equipment. Rely on your maps to help keep the different types of grain segregated and identity preserved.

 

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