Factors influencing induction, propagation and regeneration of mature zygotic embryo-derived callus from Allium cepa

A systematic study on the effects of subspecies, cultivar, basal medium, sucrose concentration and 2,4-dichlorophenoxyacetic acid concentration on callus induction, propagation and subsequent plant regeneration in Allium cepa has been carried out. Mature zygotic embryos from two onion (cvs. Sturon and Hyton) and two shallot (cvs. Tropix and Atlas) varieties were used as explants. After callus initiation and growth on both Murashige and Skoog (MS) and Gamborg's B5 modified by Dunstan and Short (BDS) basal media with different 2,4-dichlorophenoxyacetic acid and sucrose concentrations for eight weeks, lines were identified on which compact or friable callus was induced. Callus induction and propagation were largely determined by the concentration of 2,4-dichlorophenoxyacetic acid whereas subspecies, cultivar, sucrose concentration and basal media were of less importance. After callus propagation for twelve weeks, 315 lines from a total of 3348 embryos initially subcultured were selected to test their regeneration capacity on growth regulator-free medium. It was found that shallot formed more shoots and roots than onion. The MS basal medium proved to be more beneficial for shoot regeneration and root formation than the BDS basal medium. There were no differences in plant regeneration among selected calli which had been previously subcultured on different concentrations of 2,4-dichlorophenoxyacetic acid and sucrose. The results show that plant regeneration strongly depended on the line: 45.4% from 315 tested lines could produce shoots while 93.0% formed roots.