Assessing the genetic diversity in onion (Allium cepa L.) landraces from northwest Spain and comparison with the European variability

Fifteen onion landraces from Galicia (northwest Spain) were characterised with a set of 25 microsatellite markers and the genetic variability harboured by this collection was compared with the surrounding diversity by comparison with a representative panel of European onion landraces. Twenty markers were polymorphic allowing the detection of 121 alleles. Ninety-one of these were identified in the Galician group (average of 4.6 distinct alleles per locus) and 9% of the total number of alleles were recorded as unique alleles specifically contributed by onion landraces from northwest Spain. High values of observed and expected heterozygosities were detected for the majority of loci. Wright's fixation index confirmed an excess of heterozygotes and a low level of inbreeding, suggesting that high levels of heterogeneity have accumulated within landraces. Multivariate and STRUCTURE analyses revealed that Galician onions possessed a specific genomic composition different from that found in European landraces.