SEED EXPLANT MATURITY AND 2,4-D AFFECT ORGANOGENESIS OF WHITE ASH (FRAXINUS AMERICANA L.)

Abstract

At three different times throughout the growing season, white ash seeds representing different maturity levels were transversely dissected, surface sterilized, and placed on agar-solidified MS medium containing 10 μM thidiazuron (TDZ) and a factorial combination of 0, 1, and 5 μM 2,4-D and 0, 0.5, and 1 μM glyphosate. After four weeks, explants were transferred to MS medium containing 5 μM BA and 5μM NAA. After 12 weeks in vitro, the greatest percent (60%) of explants with organogenesis (adventitiously produced leafy structures that could grow into shoots) was when seeds were exposed to 1 μM 2,4-D. Organogenesis occurred on explants only exposed to TDZ (31%), therefore auxin was not necessary for, but enhanced organogenesis. Seed explants were not consistently stimulated, or inhibited by these levels of glyphosate. Compared to immature-seeds, mature see explants were the most organogenic (67%) and had the greatest amount of adventitious shoots (14%).