Genetic relationships within basil (Ocimum) as revealed by RAPD and AFLP markers

Species of the genus Ocimum, basil, are widely cultivated as a source of essential oil for use in foods, flavours and fragrances and as a culinary herb, spice and garden ornamental. Ocimum taxonomy is confused due to interspecific hybridization, polyploidization, and the existence of chemotypes or chemical races with similar morphology. Twenty-eight basil accessions, including six species O. basilicum L., O. americanum L., O. x citriodorum Vis., O. minimum L., O. gratissimum L., O. tenuiflorum L., and six botanical varieties or cultivars of O. basilicum var. basilicum 'Genovese', O. b. var. basilicum 'Sweet Basil', O. b. var. difforme, var. purpurascens 'Dark Opal' and O. b. var. thyrsiflorum, were analyzed by both random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphisin (AFLP) markers. Phylogenetic relationships were determined by neighbour joining cluster analysis based on dice distance between accessions. A very strong correlation between dice distance matrices based on RAPD and AFLP data were observed and the resulting neighbour-joining trees were congruent. High bootstrap support values for the branches separating O. tenuiflorum and O. gratissimum accessions, a cluster containing O. americanum and O. x citriodorum accessions, and a cluster containing O. basilicum and O. minimum accessions were observed in both cases giving a good representation of traditional taxonomic relationships. Within the O. basilicum cluster, similar accessions grouped together specifically O. minimum, O. basilicum 'Dark Opal' and O. basilicum var. difforme accessions. In addition to morphological, chemical and crossability data, RAPD and AFLP analyses can be a useful tool for resolving existing problems in identification and classification of basil.