THE DEVELOPMENT OF PUTATIVE ADVENTITIOUS SHOOTS FROM A CHIMERAL THORNLESS ROSE (ROSA-MULTIFLORA THUNB EX J MURR) IN-VITRO

A method has been developed for producing putative adventitious shoots from proliferating shoots of a chimeral Rosa multiflora rootstock. Pr oliferating cultures were established from greenhouse-grown axillary b uds on Skirvin and Chu's (1979) modification of Murashige and Skoog (1 962) medium supplemented with 6-benzylamino purine (BA, 2 mg l(-1)) an d naphthaleneacetic acid (NAA, 0.1. mg l(-1)). The buds typically expa nded to produce a single shoot that soon yellowed and senesced. Howeve r, when buds were transferred to the same medium with BA replaced by g ibbereIlic acid (GA(3), 0.5 to 1.0 mg l(-1)) and silver nitrate (3.4 m g l(-1)), prior to the onset of senescence, the shoots continued to ex pand and proliferate following subculture at 3-4 week intervals. Shoot s harvested from this medium were moved to the same medium supplemente d with various levels of thidiazuron (TDZ). Those subcultured on mediu m with 1 mu M TDZ developed compact nodular callus that later, after o ne or two subcultures onto the same medium, formed putative adventitio us shoots. About half of these shoots rooted on MS medium supplemented with three auxins [(NAA, 0.5 mg l(-1)); indoleacetic acid (IAA, 1 mg l(-1)), and indolebutyric acid (IBA, 0.5 mg l(-1))], GA(3) (0.5 mg l(- 1)), silver nitrate (3.4 mg l(-1)), activated charcoal (200 mg l(-1)) and sucrose (40 g l(-1)). A sample (119) of these plants were screened for their thorny or thornless condition: some parental stems had a fe w recurved thorns; petioles had small lignified hairs. All regenerants had thornless stems; but they varied in degree of petiole prickliness . This suggests that we have separated a pure thornless form from the parental clone. In addition, there is enough variation among regeneran ts to suggest that somaclonal variation has appeared.