THIDIAZURON STIMULATES SHOOT ORGANOGENESIS AND SOMATIC EMBRYOGENESIS IN WHITE ASH (FRAXINUS-AMERICANA L)

Immature and mature nonstratified seeds of white ash (Fraxinus americana L.) were dissected transversely and 2/3 of each seed was placed onto agar-solidified Murashige and Skoog medium. Adventitious buds, shoots, and somatic embryos formed on callus, cotyledons, and hypocotyls of the resulting seedlings. Shoot organogenesis was induced on explants cultured on medium with 10 muM thidiazuron but not on explants on media with benzyladenine (BA) or isopentenyladenine. Not all seed sources were equally capable of shoot organogenesis and embryogenesis. Atypical of adventitious regeneration of other woody plants, mature seed explants of white ash were more organogenic with shoots that elongated better than explants from immature seeds. Somatic embryogenesis was observed in cultures where mature seeds were first cultured for 4 weeks on a medium containing 10 muM adenine 2,4-dichlorophenoxyacetic acid in combination with 0.1 and 1.0 muM thidiazuron, followed by transfer to a medium containing 0.05 muM 6-benzyladenine and 0.5 muM naphthaleneacetic acid. Adventitious shoots and epicotyls from both seedlings and germinated somatic embryos were rooted under intermittent mist and acclimatized to the greenhouse.