There was a time when you could go out into a field of regular dent (field) corn, right around the time the kernels were at milk stage, and pick several ears to make, what was thought to be at the time, a pretty tasty meal.  Those were the good old days, right?

I don’t think so….

Finding a naturally occurring mutation of dent corn that happened to produce kernels consisting mostly of sugar rather than starch changed the expectations of all who like to eat corn with their meal.  The plant that resulted from this mutation was called sweet corn.  The problem for growers is that generally speaking, the higher the eating quality of the corn; the harder it is to grow in the field. 

Alphabet Soup of Sweet Corn

There are 3 basic types of sweet corn that are classified by the gene that gives the plant its characteristics.

• SU  – commonly referred to as Normal types, contain the “sugary” su gene.  The su type contain anywhere from a 9% to 16% sugar content.  These types tend to lose their sweetness rapidly after maturity, but have a good “corn flavor” and are the easiest to grow in the field.
   

• SE – commonly referred to as “Sugary Enhanced” contain the se gene.  These types are generally sweeter than the su types with 14% to 35% sugar content, and are known for a tender kernel, creamy texture, and good “corn flavor”.
   

• SH₂ – Commonly referred to as “SuperSweet” or “Shrunken 2” contains the sh₂ gene.  These types are the sweetest of the three types mentioned here with a sugar content of 28% to 44%.  The sh₂ gene not only gives the corn a higher sugar level, but that sugar level is maintained longer than either su or se types.  This type is the most difficult to plant and grow, due to the lighter seed, relatively poor vigor,  greater susceptibility to diseases, and the characteristic shrunken and shriveled seed.  SuperSweet types can also have a slightly tougher kernel, less of a creamy texture, and less “corn flavor”.

There are also genes called “modifier genes” that can be added to each sweet corn type to improve eating quality.  The addition of these “modifier genes” and whether one or both of the parents have the best eating quality traits are two ways to develop distinct varieties within each sweet corn type.

Solutions for sweet corn growers

Sweet corn breeders are currently combining the 3 basic types mentioned above in an attempt to get the best characteristics of each type into one variety.  One of the biggest challenges is to combine high quality eating characteristics with high vigor seed that is easy to grow in the field.  Breeders are getting closer, but still have some work in this area.

Seed Physiologists are also working to help solve the plantability and stand establishment problems of some of the high quality sweet corn varieties.  One thought, is to apply an “artificial seed coat” to the seed.  An “Artificial Seed Coat” could be helpful in 3 ways;

• it can add weight to the seed and smooth out the cracks and crevasses in a shrunken, wrinkled seed improving plantability,
   

• the coat can be formulated to optimize the rate at which moisture is absorbed by the seed, minimizing seed damage due to cool wet soil conditions, and
   

• the coat can be used as a platform to add larger quantities of materials that may be helpful in establishing stands in the field.  An example of this would be the addition of bacteria that produce a “Systemic Acquired Resistance” (SAR) in the plant.  This type of bacteria can initiate a plant immune response to help defend against diseases that are common problems when establishing high quality sweet corn varieties in the field. 

Below is a cross section of an SH₂ sweet corn seed with an experimental artificial coat.  Note the irregular, almost star shape of the seed and how the coat fills and bridges the cracks and crevasses.