Breeding for viral resistance: conventional methods

Abstract

Conventional breeding methods based primarily on the principles of Mendelian genetics have provided the basis for the majority of resistance to viruses in potato cultivars. This development of resistant cultivars has resulted from sexual hybridisation followed by selection of the best genetic recombinant. Selection is one of the most powerful tools available for crop improvement. Successful selection depends on reproducible genetic variability, ability to identify genetically superior individual plants or families, populations large enough to ensure the likely occurrence of rare genetic combinations, and the combination of resistance expression with commercial utility. Resistance to the major potato viruses namely potato virus A, potato virus M, potato virus S, potato virus X, potato virus Y and potato leafroll virus has been studied and selected for. A number of different types of resistance have been identified including (a) major gene resistance; (b) minor gene resistance; and (c) immunity. With the exception of potato leafroll virus, stable resistance to the other viruses has been achieved either singly or in combination in a range of potato cultivars. In addition for both potato leafroll virus and potato virus Y, the focus has been on the development of resistance to aphid transmission of the viruses.