Predicting Out-crossing in Grain and Seed Production Fields.
Juan Astini1, Agustin Fonseca2, Higinio Lopez-Sanchez1, Susana Goggi1, Jon Lisazo3, Mark Westgate1, and Ray Arritt1. (1) Iowa State University, 1563 Agronomy Hall, Ames, IA 50011, United States of America, (2) Monsanto company, 503 S. Maplewood, Williamsburg, IA 52361, (3) University of Florida, Crop Systems Modeling Lab, P.O.Box 110570, Gainesville, FL 32611
Potential use of maize (Zea mays L.) for production of pharmaceutical and industrial compounds has increased concern about confinement of transgenic pollen. While numerous studies have documented pollen flow in maize, there has been little success quantifying the level of out-crossing to be expected from it. The objective of this project was to predict out-crossing resulting from the dispersal of adventitious pollen and the flowering dynamics typical of grain production and seed production fields. One hectare of yellow, RoundUp Ready(TM), Bt maize was planted in the center of approximately 36 hectares of non-transgenic, white maize. In one case, the entire field was managed for normal grain production; in the second case, the white corn was detasseled in a 4:1 ratio to reduce local pollen density to a level typical of hybrid seed production. Flowering dynamics were monitored and coupled with local weather conditions to determine the timing and extent of pollen dispersal as well as the synchrony between the transgenic and non-transgenic hybrids. Out-crossing percentages were calculated by coupling the kernel set and pollen dispersal models we have developed. Approximately 90 harvest samples (up to 50000 kernels each) were collected from each field along cardinal transects (N, NE, E, SE, S, SW, W and NW) extending up to 250 m from the central plot. The level of out-crossing predicted by the kernel set model closely followed the field pattern of measured values and was highly accurate at predicting where out-crossing exceeded 0.5 %. As expected, less local pollen production resulted in greater observed and predicted out-crossing with distance from the transgenic pollen source. These results indicate that out-crossing in maize can be predicted by combining quantitative analysis of flowering dynamics, local pollen production, and adventitious pollen dispersal.