Despite its importance as a food crop throughout the world, the genetics of many potato traits is poorly understood. Great advances have been made recently in the mapping and isolation of resistances to the major pests and diseases of potato. However, genes affecting quantitative resistances and quality traits remain largely undiscovered, and QTL locations are often imprecise.

These deficiencies are largely due to the oft-quoted disadvantages of potato as a genetic system: tetrasomic inheritance, high levels of heterozygosity, inbreeding depression, infertility and self incompatility in diploid material and lack of mutants. There are, as yet, no cloned genes for QTLs of quality or resistance traits (unlike tomato). The negative aspects of potato as a genetic system would be greatly overcome with the availability of a full genome sequence. This will greatly facilitate gene isolation and allow molecular geneticists to use candidate gene approaches for trait gene discovery. This in turn will have radical effects on potato breeding.

The genome of potato (850 Mb) is being sequenced by the Potato Genome Sequencing Consortium (PGSC) an international consortium, currently comprising 13 countries. The objective of the PGSC is to elucidate the entire potato DNA sequence by the end of the year 2010. The consortium is co-ordinated by Wageningen University in the Netherlands, and there is a steering committee, on which SCRI (Dr Glenn Bryan) is the UK’s representative.  The UK, in collaboration with TEAGASC (Ireland), University of Dundee and Imperial College, London is sequencing potato chromosome 4, the same chromosome the UK is sequencing in the tomato genome project.

The genome is being sequenced using a BAC-by-BAC approach, utlising a physical map genetically linked to the Ultra High Density (UHD) map of potato which contains more than 10,000 molecular markers. The current potato physical map comprises ~7000 BAC contigs comprising two or more BAC clones and approximately 2000 of these contigs are genetically anchored to the UHD map. The first step for any chromosome is to sequence across the contigs anchored to that chromosome. A BAC end sequence (BES) resource, comprising more than 140,000 high quality reads has been developed in the USA by Dr Robin Buell.

The BES data can be used to extend out from anchored sequenced contigs. Gaps in chromosome sequences can be closed by screening the RH BAC library used for the project with marker sequences falling in to sequence gaps. The tomato genome sequence will provide a useful tool in gap closure in the potato project, as to date there appear to be high levels of conservation of gene order in the two species and the genetic maps of tomato and potato are known to be highly collinear.

For further information contact Glenn Bryan.