Factors affecting in vitro establishment and shoot proliferation of Rosa hybrida L. and Rosa chinensis minima

The effects of nodal explants collected at different plastochrones, use of various benzyladenine (BA) concentrations, sources of carbohydrates, and phases of the culture medium on shoot establishment and proliferation of Rosa hybrida L. and R. chinensis minima were evaluated. Higher numbers of shoots per explant were obtained from R. hybrida cv. Carefree Beauty explants proximal to the apical meristem than those from distal nodes. However, proliferating shoots derived from plastochrones proximal to the apical meristem had a lower number of leaves/explant and were shorter than those derived from other distal plastochrones. Although shoot proliferation increased with higher BA concentration in the medium, a concentration of 4.4 μM BA was found optimum for axillary bud-break and shoot development for R. hybrida cvs. Adelaide Hoodless and Cuthert Grant. A higher shoot proliferation rate was observed for R. hybrida cv. Carefree Beauty explants grown on a medium containing 55.5 mM fructose than 58.4 mM sucrose. However, no differences were observed for R. hybrida cv. Cuthert Grant grown on a medium containing either fructose or sucrose. The mean number of shoots/explant was higher for R. chinensis minima cv. Red Sunblaze explants grown on a liquid (4.5) than on a solid medium (1.7) for the first reculture; while no significant differences between the two phases of the medium were observed for the second reculture. However, a higher mean number of shoots/explant was observed on solid-phase (4.0) than liquid-phase medium (3.4) for the third reculture. A higher mean number of leaves/shoot was obtained on a solidified medium rather than liquid medium in the first two consecutive recultures, while no differences were observed for the third reculture. Although a significant effect of BA concentration on mean number of shoots/explant was observed for Red Sunblaze nodal explants, the influence of BA concentration decreased in the two consecutive cultures for both phases of the medium. Hyperhydricity was observed on Red Sunblaze shoots grown on the liquid-phase medium.