Humans benefited from the diversity of genetics in corn. Completion of a generation within months, easy transportation of the result of reproduction, cross pollination allowed quick selection of genetics fitting the corn growing environments. Corn breeding techniques continue to be developed to further exploit this diversity.
Other organisms affecting cultivation of corn also have genetic diversity. Selection pressure to survive and reproduce encourages favorable genes in pathogens of corn. As the Ht1 gene was widely used for resistance to Helminthosporium turcicum (Exserohilum turcicum), a gene within this fungal species population increased in the USA within about 10 years. The corn gene severely suppressed the reproduction of the more prevalent previous race, allowing quick increase in the new race. Small genetic changes in several pathogens has resulted in appearance of new corn disease problems. Goss’s wilt bacterium may have become a corn pathogen after a gene change that allowed it to move from a minor grass pathogen to causing a major disease on a few corn genotypes. Race t of Helminthosporium maydis(Bipolaris maydis) was a mutant that produced a toxin causing disfunction of the mitochondria of corn that was utilized by seed corn producers to facilitate seed production. Multiple races of Helminthosporium carbonum(Bipolaris zeicola) have evolved adaptation to specific corn inbreds while being maintained on other grasses. Diversity in potential pathogens will continue to challenge corn and diversity in corn will continue to allow selection of genotypes to resist the new race.
Hybrid corn does benefit from the genetic diversity between the two parents. Selection for grain yield when each parent covers the other’s genes that have a negative influence on plant performance often includes resistance factors to a specific race of the pathogen. Often parent inbreds are more susceptible than the hybrids. Pathogens often have the advantage of rapid reproduction, but corn has the advantage of active human’s ability to select for resistance within the diverse genetics available.
Advantages of genetic diversity applies to all species- and we should not forget that it also applies to our species. Cultural diversity among humans is also beneficial.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.