Relationship between desiccation and viability of maize pollen

Controlling pollination is necessary to ensure maximum kernel set and high levels of genetic purity in maize. Current approaches for measuring maize pollen production are fairly simple and accurate, but they do not evaluate pollen viability. A simple and reliable technique to assess loss of pollen viability during its transport in air is required to simulate the pollination process and the risk of out-crossing associated with pollen dispersal. Anecdotal evidence indicates that pollen shed from anthers remains viable longer at low temperature and high relative humidity (RH). But a direct temporal relationship between loss of pollen viability and these environmental conditions is lacking. We tested whether vapor pressure deficit (VPD) could be used to simulate the rate of pollen desiccation and subsequent loss of viability. Fresh pollen was harvested from greenhouse and field-grown plants and exposed to a range of VPD generated using a factorial combination of temperatures and RH. After exposure from 0 to 2 h to known VPD, viability of the treated pollen was tested in vitro. These tests indicated that pollen grains are released from anthers at about 55-60% moisture content, and that subsequent desiccation is a function of air temperature, RH and time. These factors were incorporated into a single relationship that described the rate of pollen desiccation for several genotypes. Pollen viability decreased linearly (r2 ranged from 0.77 to 0.93) with pollen moisture content (PMC) to zero at PMC ≈ 30%. Together, these relationships provide a simple approach to assess loss of maize pollen viability under field conditions.