Observations of corn hybrids and inbreds at flowering stage and later allows distinction of genetic differences, especially if several varieties are planted in unform conditions. Usually plant height differences are clear. Close observation of ear characters also allows distinguishing between varieties especially when grown near each other with same micro-environment. Closer observation of the plants for other morphological differences such as tassel and leaf shape and size also can allow distinguishing genetic differences, although can these can be vulnerable to confusion with the differences caused by some virus infections and poor seedling emergence.
Inbreds and hybrids differ from each other in many other genes than only those observed in mature plants. Close observation of plants at all stages show other leaf character differences that becomes obvious when plants are in identical environments. Multiple leaf character differences become obvious when observed by experienced researchers. Pure single cross hybrid seed planted in controlled soil and temperature environment will be identical to each other for many leaf characters. Modified single cross hybrids, such as when the female parent is a cross of two related inbreds, will be reflected in seedlings with slight morphological differences. Outcross plants caused by pollen blown into the hybrid seed production field will show multiple character differences among the seedlings. A seed mix accident in which two hybrids in the same sample will show two distinct seedling plant types. This is also true where one of the inbred parents was mixed in the seed production field or if contaminated with the male parent from an adjacent field.
Accident selfing problems in the seed field results in some plants not only with distinct seedling morphology, and usually smaller than the hybrid seedlings. These ‘selfs’ are also morphologically identical to each other. If compared to a sample of the female parent, these plants can be confirmed as ‘selfs’.
Professional Seed Research, Inc. has used this information and experience to evaluate purity of hybrid and inbred seed for seed companies for more than 30 years (Seedling Growout® test). 400 seed are planted adjacent to each other in uniform environment with natural light. Experienced researchers carefully observe each plant for morphological differences to identify those that are unlike the others. If all the offtypes differ from each other, it is assumed that they are from contamination from outside hybrid fields. If identical to each other then probably the source is a seed mix or possibly contamination from an adjacent seed field. If the plants are smaller for most leaf characters yet distinct from most plants and identical to each other, they are assumed to be selfs.
This method of evaluation of purity of seed samples allows for results within 2 weeks of planting, and larger samples (400 seed) than most other grow out methods. It has been used with temperate and tropical hybrids. Corn’s diverse genetics are expressed at all stages of the plant’s development.
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.