Abstract
Key messageA unique, global onion diversity set was assembled, genotyped and phenotyped for beneficial traits. Accessions with strong basal rot resistance and increased seedling vigour were identified along with associated markers.Conserving biodiversity is critical for safeguarding future crop production. Onion (Allium cepa L.) is a globally important crop with a very large (16 Gb per 1C) genome which has not been sequenced. While onions are self-fertile, they suffer from severe inbreeding depression and as such are highly heterozygous as a result of out-crossing. Bulb formation is driven by daylength, and accessions are adapted to the local photoperiod. Onion seed is often directly sown in the field, and hence seedling establishment is a critical trait for production. Furthermore, onion yield losses regularly occur worldwide due to Fusarium basal rot caused by Fusarium oxysporum f. sp. cepae. A globally relevant onion diversity set, consisting of 10 half-sib families for each of 95 accessions, was assembled and genotyping carried out using 892 SNP markers. A moderate level of heterozygosity (30–35%) was observed, reflecting the outbreeding nature of the crop. Using inferred phylogenies, population structure and principal component analyses, most accessions grouped according to local daylength. A high level of intra-accession diversity was observed, but this was less than inter-accession diversity. Accessions with strong basal rot resistance and increased seedling vigour were identified along with associated markers, confirming the utility of the diversity set for discovering beneficial traits. The onion diversity set and associated trait data therefore provide a valuable resource for future germplasm selection and onion breeding.
Highlights
Onion (Allium cepa L.) is a major horticultural crop belonging to the order Asparagales which, of the monocot orders, is second only to the Poales for global economic value (Kuhl et al 2004)
Bulbs were harvested at maturity, dried and in late 2006–early 2007, ten healthy bulbs per accession planted in pots in separate insect proof cages in a glasshouse under natural conditions
An onion diversity set, consisting of up to 10 half-sib families derived from each of 95 founder genebank accessions, was successfully produced (Table 1), and samples can be sourced from the University of Warwick
Summary
Onion (Allium cepa L.) is a major horticultural crop belonging to the order Asparagales which, of the monocot orders, is second only to the Poales for global economic value (Kuhl et al 2004). Onions are self-fertile, they are considered outbreeding crops as they exhibit severe inbreeding depression (Jones and Davis 1944; Brewster 2008). 75% of seed derived from cross-pollination produced bulbs in a field trial, whereas less than 50% of seed from self-pollination produced bulbs (Currah and Ockendon 1983). This means that most onion cultivars are heterozygous with each plant being genetically unique.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
