Assessing the genetic diversity of Spanish Allium cepa landraces for onion breeding using microsatellite markers

Onion (Allium cepa L) is one of the most valuable vegetables in the world. However, despite its global culinary and economic significance, the knowledge about onion genetic diversity and resources is limited. The Vegetable Germplasm Bank of Zaragoza (BGHZ) (Spain) holds an important A. cepa L collection, where most of the Spanish onion variability is represented. Since the genetic diversity of Spanish onion germplasm is an unexploited resource for onion breeding, a total of 85 Spanish onion landraces (A. cepa L) and 6 related Allium outgroups from the BGHZ collection were studied by means of SSR markers. The results showed that 12 out of the 18 SSR markers amplified were useful and polymorphic to distinguish all the studied onion accessions, allowing the detection of 47 alleles, with an average of 3.9 alleles per SSR, ranging from 2 to 7. Within related Allium species, the total number of detected alleles was 45, with an average of 3.7 alleles per SSR, ranging from 1 to 10. Specific alleles were obtained both in the Spanish onion landraces and in related Allium species, with cross transferability rates ranging from 25.0% to 91.7% in the six Allium species assayed. The resulting UPGMA dendrogram grouped the 91 Allium accessions according to their taxonomical classification, producing 6 main clusters, with all the Spanish onion landraces included in one cluster at a genetic distance of 0.69. These results revealed an interesting reservoir of genetic variability, useful for onion breeding, and confirmed the need to preserve these irreplaceable genetic resources. (C) 2014 Elsevier B.V. All rights reserved.