Development of intron length polymorphic (ILP) markers in onion (Allium cepa L.), and their cross-species transferability in garlic (A. sativum L.) and wild relatives

Onion (Allium cepa L.) is a popular spice and a plant of high medicinal value. Conventional breeding and genetic improvement efforts were largely limited due to self-incompatibility and heterozygosity. Recently, marker assisted breeding has significantly reduced time and labour in developing elite varieties. But very limited polymorphic and cross-transferable markers are available in onion. There is an urgent need to develop polymorphic markers in Allium to expedite and introgress desirable traits from wild relatives (which are rich bioresource of various biotic and abiotic resistance genes) to A. cepa. Considering limited availability of reliable molecular markers in Allium and wild relatives, in current study, 20,204 ESTs (3750 contigs and 8364 singletons), of A. cepa were successfully utilized for identification of over 2689 intron length polymorphic (ILP) markers. A set of 30 markers was tested for polymorphism in onion and cross-transferability in garlic and related wild species. Among these, eighteen markers amplified at least one of the accessions of A. cepa. Transferability of these ILP markers was ranged from 21.7 to 95.7% in Allium spp. Low level of polymorphism in A. cepa compared to wild Allium species is reported. Based on the Jaccard dissimilarity matrix, a neighbour-joining tree was constructed, which clustered all the 23 varieties/accessions under three groups. All the varieties of A. cepa were clearly clustered separately under group I. However, there was intermixing of varieties/accessions of A. sativum L. and wild relatives, which may possibly be due to less number of markers validated for cross-transferability. In future, larger set of markers will be used to resolve the genetic variations among wild varieties and A. sativum These 18 polymorphic ILP markers could be utilised for diversity characterization of Allium spp., varietal identification, mapping of genes and introgression of desirable traits from wild relatives.