583 PB 094 CALLUS INDUCTION AND SHOOT ORGANOGENESIS IN RHODODENDRON `BESSE HOWELLS' AND `CATAWBIENSE ALBUM'

Combinations of me auxins 2.4-dichlorophenoxyacetic acid (2.4-D). indolebutyric acid (IBA). and naphthaleneacetic acid (NAA), with isopentenylademne (2-iP) were studied in Woody Plant (WP) medium for callus induction and shoot organogenesis from leaves of Rhododendron `Besse Howells' (BH) and `Catawbiense Album' (CA). IBA was more effective than NAA and 2,4-D at inducing shoot organogenesis when combined with 2-iP. Addition of 1 uM IBA and 15 or 30 uM 2-iP to WP medium resulted in the highest percentage of explants producing shoots (90% in BH, 100% in CA), and the greatest number of shoots per explant (18.4 in CA, 10.1 in BH) after 12 weeks of culture. Shoot organogenesis also occurred using 1 uM NAA and 2-iP combinations, but me number of shoots produced was much less than for IBA treatments. 2,4-D and NAA were more productive than IBA for callus induction. Media containing l-10 uM 2,4-D plus 5 uM 2-iP. or 10 uM NAA plus 15 uM 2-iP. were me best for callus production. In studies using thidiazuron instead of 2-iP as the cytokinin, leafy buds and very short shoots developed.