The development and characterisation of a bacterial artificial chromosome library for Fragaria vesca

The cultivated strawberry Fragaria xananassa is one of the most economically-important soft-fruit species. Few structural genomic resources have been reported for Fragaria and there exists an urgent need for the development of physical mapping resources for the genus. The first stage in the development of a physical map for Fragaria is the construction and characterisation of a high molecular weight bacterial artificial chromosome (BAC) library.

A BAC library, consisting of 18,432 clones was constructed from Fragaria vesca f. semperflorens accession 'Ali Baba'. BAC DNA from individual library clones was pooled to create a PCR-based screening assay for the library, whereby individual clones could be identified with just 34 PCR reactions. These pools were used to screen the BAC library and anchor individual clones to the diploid Fragaria reference map (FVxFN).

Clones from the BAC library developed contained an average insert size of 85 kb, representing over seven genome equivalents. The pools and superpools developed were used to identify a set of BAC clones containing 70 molecular markers previously mapped to the diploid Fragaria FVxFN reference map. The number of positive colonies identified for each marker suggests the library represents between 4x and 10x coverage of the diploid Fragaria genome, which is in accordance with the estimate of library coverage based on average insert size.

This BAC library will be used for the construction of a physical map for F. vesca and the superpools will permit physical anchoring of molecular markers using PCR.