Apical and axillary meristems of Rosa hybrida Cv. First red were pretreated with various concentrations (0, 5.0, 10.0, 15.0, 20.0, 25.0 and 30.0 µM) of oryzalin (C₁₂H₁₈N₄O₆) to induce variation in vitro. The present results indicate that fifty percent survivability (LD₅₀) was obtained in 20 µm oryzalin. Both the treated and untreated meristems were cultured in Murashige and Skoog (MS) basal medium supplemented with 0.5 mg/l benzylaminopurine (BAP), 0.01 mg/l indole acetic acid (IAA), 25 mg/l adenine sulphate (Ads) and 20 µm oryzalin. The elongated shoots were rooted in the half strength MS basal medium supplemented with 0.25 mg/l indole-3-butyric acid (IBA) and about 60% rooted plants survived in the green house. A total of 28 mutants were obtained and evaluated by randomly amplified polymorphic DNA (RAPD) markers using control as untreated meristems. Out of the twenty-eight mutants, eight mutants, which deviate from the DNA banding pattern when compared with the control plants, were obtained. This result showed the efficiency of oryzalin to induce in vitro variability in hybrid rose and detect variation through molecular markers. This investigation will give a better understanding on the rose breeding program.

Key words: Hybrid rose, in vitro, oryzalin, mutation.