Mary W. George

Cytokinins, donor plants and time in culture affect shoot regenerative capacity of American elm leaves

Cytokinins, donor plants and their time in vitro as well as basal media were investigated for their influence on shoot regenerative capacity of American elm (Ulmus americana L.) leaves. Leaves excised from six 2-year-old seedlings formed adventitious shoots when placed on Driver and Kuniyuki Walnut (DKW) medium supplemented with 7.5, 15 or 22.5 μM of benzyladenine (BA) or thidiazuron (TDZ). Thidiazuron induced significantly higher regeneration percentages on elm leaves than BA, regardless of concentration used. Donor plant also affected the efficiency of shoot regeneration, with certain seedlings having 1.5 to 7 times more explants forming shoots as compared to other seedlings tested. By subculture 15, the average number of shoots per regenerating explant increased at least 3-fold for leaves on media with BA or TDZ for the one donor plant that survived continued subculturing. Leaf explants from donor plants with the highest regenerative capacity had a higher percentage of shoot formation on DKW than MS medium. Explants from productive donor plants should be placed on DKW medium supplemented with TDZ to improve shoot regeneration efficiency from American elm leaves.

Micropropagation of Lewisia cotyledon using Axillary Buds from Flower Peduncles

Lewisia cotyledon (S. Wats.) B.L. Robins. (Portulacaceae), a perennial native to the mountainous areas of the western US, was micropropagated using the lower axillary buds from flower peduncles. Successful establishment in tissue culture was genotype dependent. Driver Kuniyuki Walnut medium (DKW) supplemented with 3.5 µM 6-benzyl-aminopurine (BA) appeared to be a better basal medium for increasing and maintaining in vitro rosettes than either Murashige and Skoog medium (MS) or Woody Plant medium (WPM) supplemented with the same BA concentration, but this response was genotype dependent. Placing rosettes on MS medium supplemented with 9.8 µM indole-3-butyric acid (IBA) for 12 wk resulted in 100% rooting with an average of 16 roots per rosette. Rooted rosettes were successfully transferred to ex vitro culture and were phenotypically normal. Micropropagation of lewisia will enable growers to produce large numbers of plants rapidly for the home landscape.