USE OF MOLECULAR MARKERS IN THE EVALUATION AND INTROGRESSION OF GENETIC DIVERSITY FOR QUANTITATIVE TRAITS

Selection for quantitatively-inherited traits constitutes a major portion of the effort expended in most crop breeding programs. Although genetic diversity is available in the adapted germplasm pool for most traits, diverse germplasm sources are of interest for their potential to expand genetic variance and, thus, potential for selection gains. They also provide potential to contribute uniqueness to an agricultural world market which is becoming increasingly homogeneous and competitive. While restriction fragment length polymorphisms (RFLPs) and isozyme markers provide genetic insights into the inheritance of quantitative traits which were previously unavailable, they also are limited by their dependence upon preservation of characterized linkage disequilibria. Methods are discussed to minimize these limitations in the identification and manipulation of quantitative trait loci. Some of the unique capabilities available using genetic markers may be particularly adapted to characterization and exploitation of desirable quantitative factors from sources of genetic diversity. If so, they may provide access to a range of diversity which has been all but untouched in the record of uses of crop germplasm collections. Strategies are discussed for the efficient use of genetic markers in breeding with diverse sources of germplasm.