The early spring seedbed is a very unfavorable environment for corn seeds. Though dry seeds can be stored unharmed for many years at -20 °F or below, corn planted very early is at risk to cold injury and even death.
1. Good spring weather in Quebec, Canada in 2002 allowed for planting on April 24. 2. Snow occurring five days later covered the field. Cold imbibition resulted in seedling damage and stand loss like that shown in pictures 3 and 4, respectively.
Early planting often exposes seeds to hydration with cold water, which can cause direct physical damage. In addition, prolonged exposure to low temperatures reduces seed and plant metabolism and vigor, increases sensitivity to herbicides and seedling blights and causes oxidation damage due to the effects of free radicals in the cell (Figure 1). Free radicals are unstable molecules that damage cells and organs. This damage is similar to that which occurs in mammals during aging and sun exposure.
For decades, Pioneer plant breeders have selected within the natural variation expressed by corn genotypes to develop hybrids with strong emergence and vigor characteristics under cool soil conditions. Pioneer has recently introduced a new early-season trait called Stress Emergence. Stress emergence refers to the genetic potential of a hybrid to germinate and emerge under stressful conditions associated with early planting including cold, wet soils or short periods of severe weather. Stress emergence is not a rating for seedling disease and should not be confused with the "early growth" rating, which refers to seedling vigor after emergence.
Pioneer research scientists are continuing to work to improve early season corn performance through conventional and molecular breeding, as well as through rigorous testing of research and commercial hybrids. By identifying molecular markers and pathways associated with superior cold germination, Pioneer researchers are beginning to develop an understanding of the genetic basis of stress emergence. This knowledge should eventually lead to even stronger early-season performance in elite Pioneer corn hybrids.
Table 3. Diagnostic images of chilling and flooding damage to corn seedlings during germination and emergence.