Seed development on prematurely harvested maize ears

Up to 10% of the seeds on maize ears harvested while kernels are in early to mid-milk stage (ca. 10-20 days post-pollination) will develop to maturity if the ears are stored at July-August temperature and humidity. Mold growth and excess drying can be problems, though damaged ears without shucks, shanks, or tips work perfectly well under proper storage conditions. The most nearly ideal storage place I have found is a high shelf on a screened north porch. Onset of post-harvest development can be delayed for at least a couple of weeks by refrigerating ears (4 C) in a dry, air-tight container.

I have on occasion used this "poor man's embryo culture" technique to save stocks and crosses damaged by livestock or wildlife. Its all-or-none character for each kernel allows easy quantification and implies utility in physiological and genetic studies of seed development. Developing kernels tend to be scattered evenly among and within rows. Carbohydrates are apparently mobilized from arrested to developing kernels. Shallow injection of 0.1 ml .001% GA into the cob often stimulates development of a cluster of kernels around the injection site. Percentage of kernels undergoing post-harvest development drops almost to zero after about 20 days post-pollination, perhaps because assembly of starch synthesizing machinery reaches an "irreversible stage" at this time. Among viviparous non-alleles so far tested, only vp stimulates development of homozygous kernels on ears from heterozygous plants. Several defective-starch genes reduce propensity for development of homozygous kernels on heterozygous ears, but at least one (an unmapped "collapsed endosperm" gene) favors development when heterozygous. I'm in the process of seeing if repeated selection based on post-harvest development can produce strains with improved efficiency of grain "nutrient sinks."

Absalom F. Williams

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