Freezing Point Temperatures of Corn Seed Structures during Seed Development

Received for publication March 10, 2005. Seed in hybrid corn (Zea mays L.) production can be exposed to freezing temperatures before harvest, which may reduce quality. This study examined changes in freezing point temperature (FPT) in seed, embryo, and endosperm tissue from ears of three F1 hybrids and one F2 hybrid harvested at various stages of development and exposed to temperatures of -6 or 11(degree)C. Seed FPT decreased in a curvilinear manner from -0.5(degree)C for immature seed (>500 g kg-1 seed moisture concentrations, SMC) to below -4(degree)C when freezing was last detectable in mature seed (SMC ~~300 g kg^-1). There were no differences in FPT when seeds were frozen at -6 or -11(degree)C or at different rates (rapid vs. gradual) of temperature change. Seeds froze at the same FPT across all hybrids and years, except for one F1 hybrid in 1999. As seeds matured (SMC < 400 g kg-1), the embryo tissue had higher moisture levels than the endosperm, which resulted in the embryo freezing at warmer temperatures (-4.5(degree)C) than the endosperm (-9.2(degree)C). Immature seeds can freeze at temperatures ranging from -1.0 to -2.0(degree)C (typical of the first freeze of autumn); however, if seed has reached or exceeded physiological maturity (SMC 360 g kg-1), it is unlikely that injury will occur.