Corn diversity

​How diverse is corn? That issue is often expressed with a concern that it is becoming too narrow.  Certainly, the selection pressure for performance under today’s USA agriculture environment does move the genetics towards performance in environments that have changed during the past 40 years.  Higher plant density and more minimum tillage have increased needs for more tolerance of stresses on plants.  Other plant characteristics have also been chosen in today’s commercial needs for grain quality.
 
But is more diversity, if needed, available?  We tend to only recall the diversity in the characteristics that we see or receives our attention.  If corn is viewed from the road as we pass by fields, it looks the same in nearly every field.  If one is a student of corn, one sees a range of leaf structures, kernel depths, kernel quality, root structure, flowering timing, and tassel branches.  Measuring grain and standability differences at the end of the season shows diversity at the end of the season.  These observations of outward characteristics are not a complete analysis of the unseen diversity that may or may not be expressed- at least to us.  
 
Mutations that occur with every reproduction often do not affect physiological processes that we observe.  Some may affect some process that has no affect in current environment but may be significant later.  Maize chlorotic mottle virus became significant in Nebraska in 1976.  Although most common hybrids were susceptible, a few older inbreds were found to be resistance.  When the disease broke out in Africa, within a few years breeding programs identified genotypes with resistance.  Goss wilt, caused by a bacterium that apparently came from grasses, caused severe damage to a few popular corn genotypes, but resistance was found in other adapted corn hybrids.  Unhidden diversity within corn has continually contributed to undesirable characteristics, such as susceptibility to a ‘new’ disease and also to resistance to a potential pathogen.
 
Corn’s history of movement to multiple environments, its annual reproduction and large number of genes have contributed to an immense diversity that is available for future versions of the crop.