RFLPs and Corn Improvement
John W. Dudley
Restriction fragment length polymorphisms (RFLPs) are described in a sidebar by Rocheford. For improving corn, RFLPs can be considered "mile-markers" of specific sites on plant chromosomes. Different plants may have different forms of any one marker. By crossing two corn inbreds or genetically uniform lines used as parents of hybrids that each have a different form of the marker, segregation of the marker can be seen in the subsequent generations. For such traits as grain yield, corn-borer resistance, or kernel quality (percent of oil or protein), it has not been possible to identify individual genes or to determine the number of genes responsible for differences in these traits between inbreds.
If two inbreds have different forms of a marker and one of the traits (for example, corn-borer resistance) also differs, it can be determined whether a gene controlling corn borer resistance is located near the marker when the trait is measured on each subsequent plant or its progeny. By using four to ten markers on each chromosome, the number of genes controlling the trait can be determined. Until the development of RFLPs, each trait was known to be controlled by several genes. The effects of each gene were so small relative to environmental effects, however, that individual genes could not be identified and manipulated by plant breeders.
Work in our laboratory and several others has demonstrated the utility of RFLPs to identify genes with significant effects on grain yield and its components. Our challenge has been to develop effective ways to incorporate this technology into corn breeding programs. Several possible ways of using this technology are currently being evaluated. When adding single genes, such as Ht1, a gene for resistance to northern corn leaf blight, into a commercially usable line, RFLPs can reduce the time required to regain the genotype of the line being improved from six generations to two or three. For traits such as corn-borer resistance for which single genes previously have not been identified, identification of two or three markers associated with genes for resistance should allow use of simple procedures for adding corn-borer resistance to commercially used inbreds. We are currently devising procedures for using RFLPs to improve yield.
RFLP technology will not replace proven corn breeding procedures. It is a tool, however, that will enhance the efforts of corn breeders and speed the development of higher quality, higher yielding, more stable corn hybrids.
John W. Dudley, professor of plant genetics, Department of Agronomy
