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Kim Colavito Markesich
University of Connecticut College of Agriculture and Natural Resources Journal Jan/Feb/Mar 2004

Xiusheng Yang is developing a mathematical model that measures the drift of corn pollen under various environmental conditions. This model should prove very useful in assessing the risk of cross-pollination from transgenic plants. Yang, professor of natural resources management and engineering, is an engineer who studies, among other topics, biometeorology--the interactions between atmospheric processes and living organisms--and how materials are transported by air and water.

Yang chose corn as the sample crop because corn is a major transgenic crop. “This is a topic of great concern,” he says. “Some countries try to block transgenic grain imports using the issue of cross pollination. A couple of years ago there was an incident with a fast food chain using transgenic crop materials, and it was a big public relations matter for them.”

Yang points out that biotech plants have been grown for years. “If you look at how much transgenic corn we have been consuming in this country and for how long – there shouldn’t be safety concerns.” In fact, says Yang, it is estimated that transgenic corn is grown in more than one third of all cornfields in the United States.

Yang is more concerned with the possible environmental effects from cross-pollination of transgenic plants to related native plants. Transgenic plants are bred to overcome environmental stresses and constraints, and some believe that this breeding could produce invasive weeds resistant to any sort of control.

The goal of Yang’s research is to create a model that properly predicts pollen drift. “We have the background and the tools from our studies in meteorology and air pollution,” Yang says. The new model will consider the biological characteristics of a plant species related to environmental conditions such as atmospheric stability, turbulence intensity, and wind speed, direction, and frequency.

The first step was to conduct field experiments to determine some of the most important parameters of the model. These experiments involved planting two adjacent fields of traditional hybrid corn, one serving as receptor plot and the other as source plot to mimic the transgenic crop, and evaluating the effects on the receptor plants. Past studies of pollen drift have often used male-sterile corn in the receptor field to assess gene flow from the source field. Yang used two species of corn, male-sterile in one experiment and waxy mutant corn in another, to be the receptor plants. Male-sterile plants do not produce pollen; the waxy mutant plants do. Using the waxy mutant corn proved to be innovative in two ways. First, because the waxy mutant corn produces pollen, the experiment in which it was used more closely resembled real world situations, where corn often self-pollinates, thus preventing fertilization by other pollen. Also, using the waxy mutant corn allowed Yang to visually determine cross-pollination by the color of the corn kernels and pollen grains without using any transgenic plants. For example, self-pollinated waxy mutant corn is white, while waxy mutant corn pollinated by plants in the source plot is yellow.

“We found that because there was no possibility of self-pollination, the studies using male-sterile corn overestimated the amount of pollen transfer, and this is the method that has been used for many years,” Yang notes. “That’s quite exciting because our study will affect future experimental methods.”

In addition, Yang’s research shows that corn pollen transfer does not conform to the existing models of particle deposition. The deposition of most small particles carried by air can be accurately predicted using the concentrations of those particles in the air above the plant canopy; typically, the concentration of deposited particles will be less than the concentration in the air above the canopy. But Yang found that with corn pollen there is actually a greater concentration of pollen in the upper area within the canopy than there is above it.

Pollen drift depends on the particular species. Corn pollen is heavy and does not move very far. But pollen from other species that is smaller and lighter might prove to drift great distances.

 “By examining the process of pollen transfer we are developing a mathematical model that can be used for other species,” Yang notes. “We’ll be able to plug in characteristics of each species with environmental conditions such as wind and weather conditions. Then we’ll be able to properly review the risk of cross pollination from transgenic plants to standard crops as well as native species.”