The application of molecular markers to rice (Oryza sativa L.) in Australia

PCR based molecular markers will enhance the efficiency and effectiveness of the Australian rice improvement program. PCR based molecular markers have been developed for the fragrance (fgr) and semi-dwarf (sd-1) genes in rice. A strategy is described for determining further target characters for development of molecular markers. Breeding objectives were assessed with regard to importance, mode of inheritance, environmental influence, difficulty and accuracy of assessment, and stage of program at which the trait is currently assessed. The traits selected as candidates for development of molecular markers are: More markers for fragrance (not all desirable parent combinations can be distinguished with existing markers); disease resistance, blast (Magnaporthe grisea), bacterial blight (Xanthamonas oryzae), and sheath blight (Rhizoctonia solani); grain extension on cooking; predisposition to chalkiness; gelatinisation temperature; minor fragrance components; and seedling vigour and early establishment. Marker development for this suite of traits includes short-, medium- and long-term goals. For some of these traits PCR based markers exist, but require testing on Australian populations. Some traits require conversion of molecular markers to PCR based systems for practical application to selection programs. Other traits are mapped but require development of markers, yet others require more fundamental genetic studies. Molecular markers will be particularly important for incorporation of disease resistance into Australian breeding populations, due to the absence of these pathogens from Australia. The aim is to have marker-assisted selection operating as an integral part of the Australian rice improvement program in the short to medium term.