Rex Bernardo, University of Minnesota, 1991 Upper Buford Circle, Dept. of Agronomy and Plant Genetics, St. Paul, MN 55108-6026
A plant breeder's work and world used to be simple: he or she bred cultivars by crossing good by good and selecting the best based on field evaluations only. The development of molecular markers in the mid-1980s afforded a means of selection based on genotype in addition to phenotype. But while thousands of quantitative trait loci (QTL) have since been reported for many traits in different species, far fewer examples of successfully exploiting mapped QTL have been reported. Key lessons learned from applying markers in plant breeding include the following: (1) it is easy to detect a QTL, but often much harder to detect the same QTL twice; (2) markers have a greater impact on some aspects of breeding than on others; (3) the purpose for detecting QTL should be clearly defined before embarking on QTL detection; (4) QTL detection is not synonymous with marker-assisted selection; and (6) gain per unit cost and time, instead of gain per cycle, is important in evaluating marker applications. Future applications of markers will likely take advantage of cheaper costs for genotyping than for phenotyping.
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