Molecular breeding approaches for enhanced resistance against fungal pathogens.

Marker-assisted selection for fungal plant resistance is the most important tool in molecular breeding at the applied level. Markers for disease resistance have been sought by researchers and breeders since the discovery that genes can be linked to each other. The dearth of visual markers has been the limiting factor in their application, but that has changed with the development of techniques to detect variation in DNA. The differences in DNA are visualized as polymorphisms which currently are predominantly identified as changes in fragment size, made possible through techniques such as polymerase chain reaction, electrophoresis, fluorescent dye detection and the use of restriction enzymes. Because of the many examples of monogenic inheritance of disease resistance genes and the importance of resistance traits, the processes of marker discovery have developed in large part around disease resistance. There are now a vast number of markers for the many resistance genes to fungal diseases in numerous crop species. The integration and use of these markers takes breeding from integrating the technology in marker-assisted selection to the development of breeding strategies around marker use in 'molecular breeding'.