In vitro mutagenesis of rose (Rosa hybrida L.) explants using gamma-radiation to induce novel flower colour mutations

The hybrid tea rose (Rosa hybrida L.) cultivar, 'Pusa Mohit' was mutagenised under in vitro conditions. Single node cuttings (25 cuttings per treatment with three replications) were irradiated with different doses of gamma-rays (0, 5, 10, 15, 25, 40, 55, 65, 70, or 80 Gy) using a Co-60 source. The gamma-irradiated explants were then cultured aseptically on Murashige and Skoog basal medium supplemented with 15.53 mu M 6-benzylaminopurine (BAP) plus 0.54 mu M alpha-naphthaleneacetic acid (NAA) plus 1.44 mu M gibberellic acid (GA(3)) plus 0.8% (w/v) agar-agar to induce sprouting and shoot proliferation. The 40 Gy treatment was determined to be the LD50 dose. Explants treated at higher doses (65, 70, or 80 Gy) showed deleterious effects of ionising radiation. Few explants sprouted, showed poor growth and failed to survive after the first sub-culture. Morphological abnormalities such as fused leaves, leaf albinism, leaves with lower levels of chlorophyll, variegated leaves, and stunted growth were observed at intermediate doses (25, 40, or 55 Gy). Decreased shoot lengths, numbers of roots per shoot, and root lengths were observed at 55 Gy. In vitro-raised mutant plants and non-irradiated (control) plants were transferred to plastic pots 1 month after acclimatisation under laboratory conditions and examined for their morphological traits. Marked variations were recorded between the mutated and control populations. Four flower colour mutants with altered or novel flower colours compared to the original flower colour were isolated. These mutants were multiplied on a large-scale through micropropagation and evaluated for their stability. This study developed a mutagenesis protocol that could be used to develop novel colour mutants in rose.