keywords: A. cepa, A. fistulosum, A. sativum, Molecular diversity, Nigeria
To understand the extent of genetic diversity among local races of Allium species is an important prerequisite for proper plant conservation and genetic resource utilization. This study was conducted to assess the genetic relatedness and diversity in 10 onion (A. cepa L.), 4 garlic (A. sativum L.) and 3 bunching onion (A. fistulosum L.) local races representing various states in Nigeria using eight RAPD markers. In addition, the study included the evaluation of cross-species transferability in the 3 Allium spp. based on six expressed sequence tag (EST-SSR) bulb onion and three genic Welsh onion SSR markers. All the RAPD markers were polymorphic, the total of 66 alleles detected ranging from 4 to 10 (mean 8.25) alleles per locus. Across all the loci, the resolving power (Rp) for the RAPD markers varied from 2.11 to 5.05 (mean 4.18). The results showed that the 3 Allium species contained considerable moderate genetic diversity. Hierarchical neighbor-joining cluster analysis (NJ) based on Jaccard’s dissimilarity matrix of the RAPD data clustered the 17 local races into three major groups (GI, II, III) corresponding to species types, two of which (GI and GII) were further divided into two sub-groups. Furthermore, the factorial analysis clearly showed three groupings, each group represented each type of species used in the study which were similar to the groupings in the NJ-based clustering with some minor differences. In total, the frequency of transferability of EST-SSR and genic SSR loci was from 65 to 100 % and 47 to 100 % respectively across all local races. A total of 13 alleles were detected using the EST and genic SSR loci in the 17 local races, ranging from 1 to 3 with an average of 2.3 alleles per polymorphic locus. Six of those 9 primer pairs were monomorphic in the 17 local races. This assessment demonstrated the potential of RAPD markers in elucidating clear genetic relationship and diversity among the studied species. This result suggests that these SSR markers could be used to analyse the genetic diversity and phylogenetic relationships in a large set of Allium species in the future.