Del Voight Penn State Extension as in Roth Email.
Here is a blurb from Purdue's April 13 newsletter (http://extension.entm.purdue.edu/pestcrop/2012/issue3/index.html#early) recently: One of the risks that newly planted corn faces is that of imbibitional chilling injury due to cold soil temperatures during the initial 24 to 36 hours after seeding when the kernels imbibe water and begin the germination process. In response to the imbibition of water, kernels naturally swell or expand. If the cell tissues of the kernel are too cold, they become less elastic and may rupture during the swelling process. Symptoms of imbibitional chilling injury include swollen kernels that fail to germinate or arrested growth of the radicle root and/or coleoptile following the start of germination. Instances of chilling injury following germination during the emergence process can also occur, often causing stunting or death of the seminal root system, deformed elongation of the mesocotyl (the so-called "corkscrew <http://www.agry.purdue.edu/ext/corn/news/timeless/Corkscrews.html> " symptom) and either delayed emergence or complete failure of emergence (i.e., leafing out underground).
It is not clear how low soil temperatures need to be for imbibitional chilling or subsequent chilling injury to occur. Some sources simply implicate temperatures less than 50°F (10°C). Others suggest the threshold soil temperature is 41°F (5°C). Daily minimum soil temperatures at the 4-inch depth (typical depth for National Weather Service measurements) have certainly dropped into the mid- to high-40's°F in recent days, with some growers reporting temperatures as low as 40°F at seed depth.