FACTORS INFLUENCING INDUCTION, PROPAGATION AND REGENERATION OF MATUREZYGOTIC EMBRYO-DERIVED CALLUS FROM ALLIUM-CEPA

A systematic study on the effects of subspecies, cultivar, basal mediu m, sucrose concentration and 2,4-dichlorophenoxyacetic acid concentrat ion on callus induction, propagation and subsequent plant regeneration in Allium cepa has been carried out. Mature zygotic embryos from two onion (cv. Sturon and Hyton) and two shallot (cvs. Tropix and Atlas) v arieties 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 prop agation were largely determined by the concentration of 2,4-dichloroph enoxyacetic acid whereas subspecies, cultivar, sucrose concentration a nd basal media were of less importance. After callus propagation for t welve weeks, 315 lines from a total of 3348 embryos initially subcultu red were selected to test their regeneration capacity on growth regula tor-free medium. It was found that shallot formed more shoots and root s than onion. The MS basal medium proved to be more beneficial for sho ot regeneration and root formation than the BDS basal medium. There we re no differences in plant regeneration among selected calli which had been previously subcultured on different concentrations of 2,4-dichlo rophenoxyacetic acid and sucrose. The results show that plant regenera tion strongly depended on the line: 45.4% from 315 tested lines could produce shoots while 93.0% formed roots.