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%).
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.