ABSTRACT
The potential value of genetic markers, linkage maps and indirect selection in plant breeding has been known for over 80 years. Yet, it is only recently that advances in automated DNA marker-screening technology have presented the precision, convenience, speed and level of throughput that has allowed marker-assisted selection (MAS) to have a significant impact on modem plantbreeding programs. The use of DNA markers for indirect selection offers the greatest potential gains for quantitative traits with low heritability, as these are the most difficult traits to select based on phenotypic response. However, developing marker-assisted selection systems for complex traits is quite difficult. This is largely due to the effects of genotype-by-environment (GE) interaction and epistasis. Precise phenotypic evaluation in several locations and seasons is essential to measure these effects and accurately estimate the relative contribution and stability of underlying quantitative trait loci (QTL). In addition, the use of large mapping populations is critically important to facilitate the dissection of quantitative traits such as tolerance to drought and resistance to insect pests that comprise many component traits each with a complex genetic basis.
