Genomic Mapping of Sugarcane and Its Potential Contribution to Improvement and to Selection of New Varieties

In diploids, crop improvement has been assisted by genome maps, but the traditional maps based on visible mutations that are simply inherited cannot be applied to polyploids. In addition, morphological markers are few in number, they often interact epistatically and in a dominant.recessive manner, and may exert such a strong effect as to be undesirable in a breeding programme. Molecular marker mapping overcomes these problems and will be of considerable value in sugarcane breeding and selection. Current research in sugarcane genome mapping involves use of restriction fragment length polymorphism (RFLP) and polymerase chain reaction (PCR) technologies to develop linkage groups ofsingledose DNA polymorphisms (SDRFs). A preliminary genome map has been developed for Saccharum spontaneum and maps are underway for S. officinarum and S. robustum. Long before the genome is mapped, molecular markers will be used for assessment ofgenetic diversity and detection of major genes. Genetic diversity measures will be used to identify varieties and safeguard any proprietary interests, to select commercial lines as parents, and to develop phylogenetic and evolutionary relationships among the Saccharum species. Detection of major genes by their linkage to markers will be used for crop improvement by introgression of a few important genes, such as disease resistance, into otherwise agronomically desirable varieties. The saturated genome map will be used to breed and select for quantitative traits and ultimately to direct crop improvement by map-based cloning.