Effect of Hormonal Combination of Auxin and Cytokinin on Micropropagation of Eastern Lily (Lilium oriental hybrid ‘Casablanca’) Plant Using Bulb Scale Explant

Introduction Lily, a member of the genus Lilium, belonging to the Liliaceae family is one of the most important commercial pot and cut flower species and one of the three major bulb crops in the commercial market because of its large, colorful and fascinating flowers. Lily hybrids are the most economically important plants with varied flowers. Hybrid Eastern lily (Lilium oriental hybrid ‘Casablanca’) is a perennial bulbous plant that its propagation by bulb in natural condition is time-consuming, so produces 1–2 bulblets per bulb scale in one years’ time which is not sufficient for large scale cultivation of this plant. One of the most important and best methods for vegetative propagation and breeding of lilies is in vitro bulb scale culture. In vitro adventitious bud regeneration from scales of Lilium rely on many factors like cytokinin and auxin concentrations such as BA and NAA. The successful use of tissue culture techniques for rapid propagation of some species of the genus Lilium including L. ledebourii, L. orientalis, L. longiflorum, L. japonicum, L. speciosum, L. concolor, L. nepalense, L. regale, L. oriental hybrid, L. Asiatic hybrid has been reported. The purpose of the current study was to evaluate the effect of different concentrations of BA and NAA on in vitro proliferation of Lilium oriental hybrid ‘Casablanca’ using bulb scale as explant to establish a suitable protocol.Materials and Methods Effect of various concentrations of 6-benzyle adenine (BA; 0, 0.5, 1 and 2 mg l–1) and ɑ-naphtaleneacetic acid (NAA; 0, 0.1, 0.2 and 0.4 mg l–1) were evaluated on in vitro proliferation of L. ‘Oriental’. Bulb scale as explant and MS basal medium as culture medium were used. Activated charcoal was applied to inhibit the browning of the culture medium and explant. The experiments were conducted in completely randomized design (CRD). The 16 treatments were applied, each treatment had 4 replications and each replication had 4 individuals. Therefore, in these experiments, a total of 192 bulbs were used. Traits including total plantlets fresh weight, leaf length, leaf number, bulblet weight, bulblet diameter, bulblet number, survival percentage, root length and root number related to in vitro proliferation were measured. All the statistical analyses were done by using SAS and Tukey’s test. Arcsin software was used for changing percent data.Results and Discussion The interaction effect of BA and NAA was significant for all measured traits. Results showed that the maximum number of bulblet (8.66) and root (5.36) were obtained in culture medium enriched with 0.5 mg l–1 BA together with 0.4 mg l–1 NAA. Culture media supplemented with 0.5 mg l–1 BA together with 0.2 mg l–1 NAA and 1 mg l–1 BA together with 0.1 mg l–1 NAA with induction of 7.33 bulblets per explant were suitable media. The largest number of leaf (4.33) was measured in culture medium containing 1 mg l–1 BA together with 0.1 mg l–1 NAA. The highest bulblet weight was measured in culture medium supplemented with 1 mg l–1 BA along with 0.2 mg l–1 NAA. The greatest survival rate (100%) was observed in medium enriched with 0.5 mg l–1 BA together with 0.1 mg l–1 NAA. Survival rate (90%) in explants treated with 2 mg l–1 BA along with 0.4 mg l–1 NAA was high. Obtained results revealed that the presence of both BA and NAA in culture media for enhancement of most traits is necessary and critical. Plantlets were transferred to a growing medium containing cocopeat, peat moss and perlite in identical proportion for acclimatization following proliferation. Approximately, 90% of regenerated plantlets survived and were morphologically similar to the mother stocks. This study will help the producers and breeders for commercial and improvement purposes. The effective role of the simultaneous presence of both auxin and cytokinin in the culture medium in effective organogenesis was shown in the present study. Similar findings were reported for some lilies such as L. ledebourii (Baker) Bioss., L. longiflorum and L. regale. Auxin was effective in stimulating bulb production and growth of the aerial part of the eastern lily, and its presence along with cytokinin is essential for leaf induction. Some studies have reported similar results. The type and optimal concentration of plant growth regulators (PGRs) in the culture medium for suitable in vitro propagation varies in different species. Genetic variations (species type), differences in the amount of endogenous production of PGRs and their interaction with each other are among some reasons for this difference. The proper ratio of auxin and cytokinin in the culture medium is effective for inducing cell division, cell differentiation, organogenesis and finally for achieving a complete plant. Root production with appropriate quantity and quality leads to the suitable survival of seedlings resulting from the growth of cultured explants under in vitro conditions and adapted plants. Current study showed that the presence of both BA and NAA is better than the presence of one of these two PGRs for induction and growth of root. Some similar findings were reported, however in most studies, the presence of auxin as individual PGR has been found to be more suitable for root induction.