A highly efficient in vitro cranberry regeneration system using leaf explants

A very efficient adventitious regeneration (shoot organogenesis) system for cranberry (Vaccinium macrocarpon Ait.) leaves was developed. A basal mediu m consisting of Anderson's rhododendron salts and Murashige and Skoog's (MS ) organics, supplemented with 10.0 mu M thidiazuron (TDZ) and 5.0 mu M 2ip, was effective for adventitious regeneration from leaves for the five cranb erry cultivars tested: 'Early Black', 'Pilgrim', 'Stevens', 'Ben Lear', and 'No. 35', Parameters examined included: 1) varying combinations of three p lant growth regulators (TDZ, 2ip, and NAA); 2) explant orientation (adaxial vs. abaxial side in contact with the medium); and 3) leaf position relativ e to the epical meristem from the source plant. Cultivars varied in regener ation frequency, but cultivar x growth regulator interaction was nonsignifi cant, With optimal treatment conditions, regeneration occurred on more than 95 % of the explants, with 'Early Black' and 'Pilgrim' producing as many a s 100 shoot meristems per explant. At all concentrations tested, NAA (as lo w as 0.1 mu M) increased callus formation and significantly reduced regener ation. Emerging adventitious shoots were always observed on the adaxial sid e of the leaves regardless of explant orientation on the medium, Regenerati on was much greater when the abaxial side was in contact with the medium, a nd was not related to leaf position on the source plants. Elongation of adv entitious shoots began approximate to 2 weeks after transfer to the basal m edium without growth regulators. Cuttings of elongated shoots rooted 100% b oth in vitro in the basal medium and ex vitro in shredded sphagnum moss. Th e high regeneration efficiency achieved by using this system will be very u seful in the application of techniques, such as Agrobacterium- and particle bombardment-mediated transformation. Chemical names used: 1-phenyl-3-(1,2, 3-thiadiazol-5-yl) urea (thidiazuron, TDZ); N-6-(gamma-gamma-dimethyallylam ino) purine (2ip); alpha-naphthaleneacetic acid (NAA).