Survival of maize (Zea mays) pollen exposed in the atmosphere

The ability of maize pollen to remain viable during exposure in the atmosphere can potentially have an overriding effect on outcrossing distances in maize. The survival of maize pollen was determined for various lengths of exposure to atmospheric conditions outdoors. Maize pollen was freshly collected from dehiscing anthers of maize plants and immediately exposed to direct sunlight and to the air. Pollen viability was assessed using in vitro germination tests. The length of exposure time required for pollen germination to be reduced by 50% ranged from 60 to 240 min, depending on environmental conditions. Pollen viability was found to be relatively insensitive to solar radiation and was affected most by loss of moisture, which depended on the energy input from the sun and on the vapor pressure deficit of the ambient air. Maize pollen germination was described well for a wide range of environmental conditions by the integral over time of the vapor pressure deficit of the air. These findings were combined with previously determined values for the water vapor conductance of pollen walls and with a relationship for pollen germination as a function of pollen relative water content to arrive at an equation for predicting the dynamics of pollen survival as a function of exposure to the environment. This model successfully predicted germination percentage over at least a two-decade range for maize pollen freshly collected from anthers.