Active shoot cultures of Rhododendron ‘Aglo’, ‘Molly Fordham’, and ‘Scintillation’ were maintained on four levels [10, 20, 30, and 40 μ M (2, 4, 6 and 8 ppm)] of N6-(2-isopentenyl)adenine (2iP) for five months. Growth characteristics were evaluated at three and nine months post-acclimatization (PA). Differences in height or width were no more than 4 cm (1.6 in), and differences in branching were five branches or less. R. ‘Molly Fordham’ plants exhibiting a dwarf, brooming nature were generated from all 2iP levels, and accounted for 3–5% of all plants grown. R. ‘Molly Fordham’ plants generated from 26-week-old cultures were initially 13% taller at three months PA, and then 6% wider at nine months PA when compared to plants generated from 240-week-old cultures. Leaf area for plants generated from 26-week-old cultures was 12 or 23% greater than for plants from 240-week-old cultures. Variant plants were generated from the 26- and the 240-week-old cultures at 9% and 5% respectively, although the difference was non-significant. Rooted microcuttings (bases) of R. ‘Aglo’, ‘Molly Fordham’, and ‘Scintillation’ were cut half-way up the stem, and the top half (retips) were rooted also. The retipping procedure produced bases that had an increased branching development (12 or 69%). The population of R. ‘Molly Fordham’ bases produced variants (9%), although the population of retips did not (0%).

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Author notes

Scientific contribution no. 1577 of the Storrs Agricultural Experiment Station. This research was supported in part by grants from the American Rhododendron Society, 201 South State St., Bellingham, WA 98225; the Horticultural Research Institute, 1250 I St., N.W., Suite 500, Washington DC 20005; and the Storrs Agricultural Experiment Station, Storrs, CT 06269.

2Research Assistant, and former graduate student.

3Associate Professor.