Numerical simulations and field studies of maize pollen dispersion

Controversy over use of genetically modified (GM) crops has led to requirements for evaluating and controlling the potential for inadvertent outcrossing in open pollinated crops such as maize. In response we are developing an Adventitious Pollen Risk Assessment (APRA) model that couples physical and biological processes affecting maize pollination based on field and laboratory measurements of maize pollen transport and viability. The core of the APRA model is a Lagrangian model of pollen dispersion. The Lagrangian method allows each element of the material being transported to be identified by its source, time of release, or other properties of interest. This permits straightforward establishment of source-receptor relationsprovide and the ability to trace the environmental conditions to which the pollen has been exposed in its travel from tassel to silk. Thus the physical effects of wind and turbulence on pollen dispersion can be considered together with the biological aspects of pollen release and viability. APRA includes evaluation of the biophysical factors that affect pollen viability.

Predictions of pollen dispersal by the Lagrangian model compare well both to observations and to results from a standard Gaussian plume model. Preliminary results indicate that pollen viability can be quantified by an "aging function" that accounts for temperature, humidity, and time. Decline of viability with time is nearly linear when elapsed time is multiplied by a factor that depends on temperature and vapor pressure deficit. A second biological component of the APRA model is specification of the diurnal trend of pollen shed, and especially the relation of pollen shed to ambient meteorology. We present results from a field experiment to measure diurnal pollen shed and its relation to local temperature, humidity and wind, and show the influence on deposition that results from correlation of pollen shed with fluctuating meteorological conditions.