Corn genetic diversity

​Corn’s history and biology has resulted in diversity beyond what most of us see in any single season.  Advantages of hybrid plant uniformity for yield, harvestability, disease and pest resistance and genetic repeatability requires development of homozygous inbred parents.  Each of many seed companies produce multiple hybrids each year and there are about 40,000 genes in each corn plant that are available to influence something, whether needed or not.  
 
Corn researchers in 1920’s became aware of a need to collect and share many of the genetic sources in corn, forming a Maize Genetics Cooperation Stock Center- it’s history is summarized at http://maizecoop.cropsci.uiuc.edu/mgc-info.php. This collection started and continues to emphasize mutants affecting some identified trait, such as those involved in sweet corn, waxy corn or amylose corn and many that may not have a specific economic advantage but are useful in understanding some biochemical pathway in the corn metabolism.  Study of these mutants contributed to location of genes on each chromosome and add to growing knowledge of corn DNA codes for many traits.  
 
Despite these efforts, corn’s genetic diversity is large due to selection by humans over diverse environments.  Our experiences with ‘new’ diseases as a pathogen such as the bacterium causing Goss’ wilt suddenly appears, with a previously unknown susceptibility gene in corn became part of popular corn hybrids, or susceptibility of race T of southern corn leaf blight associated with mitochondrial gene in t-cytoplasm male sterile corn.  Resistance to Maize Chlorotic Mottle Virus was found in corn genetics in USA after it occurred in Kansas in the 1970’s and in Africa in 2016.
 
Often the strong resistance to these diseases are associated with single genes already present in corn apparently without intended human selection and without known selection pressure in absence of the disease.  Perhaps there was exposure somewhere in its history where the gene was favored but also it is likely that randomness of mutations, segregation of genes during miosis, cross pollination and historic diversity of corn’s environments have provided many genes for characters that we have yet to identify.  These genes must be influencing multiple internal aspects of absorption of light wavelengths, translocation of carbohydrates, absorption and movement of minerals, water uptake and conservation, and structures of leaves.  Among this diversity is the future adaptation needed for changing environments.
 
Breeders witness diversity within their nursery as they see differences in plant structures and growers see differences among hybrids in performance each year.  At Professional Seed Research Inc., we see differences among hybrids in structures of seedlings (Seedling Growout®).  Genetic diversity will continue to be an important contributor to this crop as it interacts with changing environments.