Genetic diversity in European Pisum germplasm collections

The distribution of genetic diversity among 4538 Pisum accessions held in six European Genebanks has been studied in order to identify sources of novel genetic variation, the extent of overlap between the collections and to understand the overall structure of genetic diversity in Pisum. Molecular marker analysis was based upon presence/absence polymorphism of retrotransposon insertions, scored by a high-throughput microarray approach. We conclude that the diversity of Pisum constitutes a broad continuum, with graded differentiation into sub-populations which display various degrees of distinctness. The most distinct genetic groups correspond to the taxa P. abyssinicum and P. fulvum, followed closely by P. sativum cv Afghanistan. P.elatius accessions are broadly distributed and consistently intermingled with P.sativum in several analyses, indicating that the former is the progenitor of the latter. The cultivars and landraces of P.sativum can be divided into two broad types, one of which is strongly enriched for modern cultivars. The addition of germplasm sets from five European Genebanks, chosen to represent high diversity, to a single Collection previously studied with these markers resulted in modest additions to the overall diversity observed, suggesting that the great majority of the total genetic diversity collected for the Pisum genus has now been described. Two interesting sources of novel genetic variation have been identified and we have proposed sets of representative core accessions with a range of sample sizes for future study and exploitation.