Corn Breeding: Types of Cultivars

This is the third in a series of lessons specifically designed to instruct individuals without any formal training in genetics or statistics about the science of corn breeding.  Individuals with formal training in genetics or statistics but without any training in plant breeding also may benefit from reading these lessons.

A cultivar is a plant variety that has been developed for a specific use, such as production of grain.  The most common type of corn cultivar grown today and since the middle of the 20^th century by U.S. farmers is the single-cross hybrid. In the 1930’s and 1940’s, double-cross hybrids were more prevalent. Before double-cross hybrids, farmers raised open-pollinated varieties. In this lesson, the development and production of these and other types of corn cultivars will be described. The advantages and disadvantages of types of cultivars other than single-cross hybrids that could be grown by farmers also will be discussed. The lesson begins with a brief description of genes and alleles, which will be helpful in understanding some of the differences among types of cultivars.

Objectives

At the completion of this lesson you will be able to

• define gene, allele, locus (plural is loci), genotype, phenotype, homozygous, and heterozygous,
• describe hybrid vigor and genetic segregation, and 
• explain the differences among the following types of cultivars:
  • inbreds
  • single-cross hybrids
  • double-cross hybrids
  • open-pollinated varieties
  • populations and synthetics
  • population x population crosses
  • inbred x population crosses.