Assessment of genetic diversity and phylogenetic relationships in Asparagus species related to Asparagus officinalis

Eight species of the genus Asparagus, members of the group of European species closely related to A. officinalis, were analysed using internal transcribed spacer (ITS), and expressed sequence tag-derived simple sequence repeat (EST-SSR) markers, as well as cytological observations of their hybrids, to study their phylogenetic relationships and the possibility of broadening the narrow genetic base of cultivated varieties. Phylogenetic analysis using ITS data revealed two major clades: clade I consisting of A. acutifolius and clade II (referred to in this study as the ‘officinalis group’) comprised of sequences derived from species closely related to A. officinalis; but the different species within the ‘officinalis group’ could not be clearly separated. In contrast, cluster analysis of EST-SSR marker data showed six major clades and clearly separated each population, grouping most of the genotypes from each population together. That is, EST-SSR markers were found to be more informative than ITS markers about the relationships within the ‘officinalis group’, indicating that EST-SSR markers are more useful than ITS sequences for establishing phylogenetic relationships at the intrageneric level. All the crosses carried out at the same ploidy level were successful. The high crossability, together with the regular meiotic behaviour and high pollen and seed fertility observed in the interspecific hybrids analysed, suggest relatively close relationships between the species studied. We conclude that the group of species classified in the ‘officinalis group’ are in the primary gene pool, indicating that these species could be used to increase the genetic diversity of the cultivated species. In addition, the tetraploid landrace “Morado de Huétor” could be employed as a bridge to generate new cultivated germplasm.