POTENTIAL OF INTERSPECIFIC HYBRIDS IN THE GENUS ASPARAGUS

Interspecific hybridization is a very important tool to introduce new characters into a crop. The genus Asparagus contains more than one hundred hermaphrodite and dioecious species. Previous reports indicated that Asparagus officinalis (garden asparagus) and A. densiflorus crosses did not give interspecific hybrid plants. In contrast, we successfully obtained interspecific hybrids between A. officinalis and A. schoberioides and presented the results at Xth International Asparagus Symposium. Phylogenetic relationships among Asparagus species may be useful for choosing the most appropriate wild relatives. To construct the phylogenetic tree of Asparagus species, we used eighteen species including three subgenera, Asparagus, Myrsiphyllum and Protasparagus, and sequenced approximately 250 bp of internal transcribed spacer 1 (ITS1). Phylogenetic analysis indicated that the species of subgenus Asparagus consists of a monophyletic group and the species of subgenus Protasparagus comprises a potentially paraphyletic assemblage. The results also showed that garden asparagus and A. schoberioides were closely related in the subgenus Asparagus, and A. densiflorus was placed at the most basal position in the genus Asparagus. Genetic distances of these species are probably correlated with the possibility to generate interspecific hybrids. We have crossed A. officinalis, A. asparagoides, A. cochinchinensis, A. densiflorus, A. kiusianus, A. schoberioides, A. virgatus, and A. verticillatus, but only crossings between A. officinalis and A. schoberioides and A. officinalis and A. kiusianus gave interspecific hybrid plants. The correlation between the phylogenetic relationship of Asparagus and the potential of interspecific hybridization with garden asparagus is reported.