Other Types of Hybrids

Some farmers in the United States and many farmers in some parts of the world either want or need to produce their own corn seed.  Reasons could include non-availability of single-cross hybrid seed, the high cost of single-cross seed, or the farmer may be producing corn for a small niche market that requires special traits that are not available in any single-cross hybrids.  Growing populations is one alternative for these farmers, but this option does not allow the farmer to take advantage of hybrid vigor that could result from crossing two cultivars to form a hybrid.

Producing their own single-cross or double-cross hybrids likely is not economically feasible for most farmers.  Are there alternatives?

Both single-cross and double-cross hybrids are produced from inbreds.  However, hybrids can be produced by crossing types of cultivars other than inbreds.  For example, a population hybrid is produced by crossing two populations.  How much hybrid vigor would be realized in a population cross would depend on the populations used.

Producing any type of hybrid requires controlled pollinations to achieve complete cross pollination. Often this is accomplished by detasseling one of the parents. Detasseling a population would be difficult for two reasons.  First, plants of a population usually are relatively tall.  Secondly, removal of all tassels would require continual walking of the fields over a period of a week or more because the plants in most populations are quite variable for occurrence of flowering. 

Both of these difficulties (tall plants and variable maturity for flowering) could be overcome by crossing a population (the male parent) to an inbred (the female parent) or to a single-cross of two related inbreds. Most inbreds have relatively short plant height. Also, because all plants of an inbred or single-cross are genetically identical, flowering occurs over a relatively short period of time and complete detasseling could be accomplished in less time than for a population. 

Although most of the best inbreds are privately owned, public inbreds that could be used by farmers to produce population x inbred hybrids are available. Furthermore, a farmer could genetically improve a population x inbred hybrid by conducting selection in the population for enhanced performance when crossed to the inbred. Procedures for doing this type of testcross selection are outlined in subsequent lessons.