The Ht1 gene for resistance to the fungus causing northern leaf blight, Exserohilum turcicum, was effective during the 1970’s. This was before new races of the fungus that overcame the single resistance gene. One could detect the presence of the gene by putting the fungus on greenhouse-grown seedlings and evaluating for the distinctive resistance lesion that developed in about 10 days. As more inbreds, hybrids and segregating breeding materials were evaluated, it became clear that each corn genotype had distinct leaf morphological characters expressed in these young seedlings. Inbreds that had been deemed as pure from years of self-pollination had exactly identical expression of these characters, but segregating materials showed lack of uniformity in seedling morphology.
Previous experience with observations of late emerging plants that eventually resulting into deformed mature plants due to competition with adjacent corn plants led to the conclusion that one could evaluate for seed purity by observing seedlings closely in controlled greenhouse conditions. This led to a series of experiments and observations and eventual understanding that close observations of seedlings for certain key morphological features would allow evaluating genetic purity of hybrid and inbred seed lots. This technology has been applied by Professional Seed Research Inc. (PSR) since 1988 to multiple temperate and tropical hybrids for evaluation of purity (Seedling Growout®). Each corn genotype is distinct with seedling leaf morphology.
Close observation of seedling morphology also is implemented in corn breeding. As a trait is being crossed into an inbred, the segregates are formed with each generation of crosses, plants expressing the trait and having the most characteristics of the original parent can be selected for the next cross. Because the method allows observation of a large number of plants in a small space, this method can cut the number of generations needed to recover the desired inbred with the trait. PSR calls this corn backcrossing service Phenotype Select™.
Strange and fascinating how curiosity of those late emerging plants in the field and observations of seedlings could lead to new technology. Variables in crop-growing has provided many opportunities for participants to develop machinery and specific methodology for improving crop production.
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.