Future directions: Association Mapping
Association mapping can also be used for QTL discovery and to identify marker/trait correlations, but uses large sets of unrelated accessions rather than specifically developed populations.
The advantage is in not needing to develop traditional mapping populations; however, the efficiency is highly dependent on the level of linkage disequilibrium, which differs among crops, and many markers may be needed.
See Breseghello and Sorrells 2006 for a good discussion, and Weber et al. 2008 as an example.