Effect of Medium and Plant Growth Regulators on Micropropagation of Pepino (Solanum muricatum Aiton) in vitro Condition

Introduction: Pepino (Solanum muricatum Aiton) is a diploid herbaceous plant belongs to the Solanaceae family, which is growing in subtropical zone, originates from Andes in South America. It is commercially grown for its fruit, which is appreciated not only for food but also for its appearance, in South American countries, including Bolivia, Colombia, Ecuador and Peru, as well as in countries such as New Zealand and Australia. Pepino is propagated by seed, cutting, and tissue culture methods. Most pepino cultivars are sexually fertile and produce viable seeds, but their seeds have poor germination and high level of heterozygosis causing to highly variable plants. Both mentioned negative aspects have limited the mass production of this plant through seed. In this case, stem cutting is used as the most common way of propagating pepino led to transmission of viral diseases and increasing propagation costs as two main limiting factors of pepino propagation. So, micropropagation systems are a promising tool to produce disease-free clonal plant material with low costs. Therefore, the present study was aimed to assess the effect of different media and plant growth regulators on micropropagation traits of pepino.Materials and Methods: Three separate experiments were carried out in institute of plant sciences of Ferdowsi University of Mashhad in 2016. Pepino seeds were bought from company of Plant World Seed, UK, were cultivated on MS medium. Grown plants were used as source of providing explants. Four mediums, including MS, ½ MS, SH and B5 were used to determine the best culture medium for shoot regeneration of pepino using single node explant. A factorial experiment was conducted based on a completely randomized design. Some growth properties such as number of shoots, shoot length, number of roots, root length, leaf number and leaf length were evaluated after two and four weeks. In proliferation experiment, MS medium was compared with MS supplemented with different concentrations of BA (0.5, 1 and 2 mg L-1) and Kin (0.5, 1 and 2 mg L-1) applied as combined treatments, and also BA used alone at concentrations of 2, 4 and 6 mg L-1 that was conducted based on a completely randomized design. For rooting of explants, an experiment was conducted based on a completely randomized design containing of two concentrations of IBA (at 0.3 and 0.6 mg L-1) and three concentrations of NAA (at 0.3, 0.6 and 0.9 mg L-1) in MS medium. Some growth properties including root number and length, root density and root quality were evaluated after four weeksResults and Discussion: Results indicated that micropropagation rate of pepino was affected by culture medium type. The highest shoot length, number of root, root length and leaf number were obtained in MS medium, although statistically there was no significant difference between MS and ½ MS media. The highest number of shoots and leaf length were observed in MS medium, which led to a significant difference with other media (½ MS, SH and B5). Overall, Based on obtained results MS medium was the best culture medium for micropropagation of pepino using single node. In the proliferation experiment, the highest shoot and leaf number and plant color were obtained with using 2 mg L-1 BA + 1 mg L-1 Kin, whereas the highest shoot length and leaf length were observed in the 1 mg L-1 BA + 2 mg L-1 Kin and 1 mg L-1 BA+1 mg L-1 Kin treatments, respectively. Increasing in concentration of BA up to 2 mg L-1 in combination with Kin had a positive effect on shoot proliferation, while applying BA at concentration 2, 4 and 6 mg L-1 alone led to decrease in proliferation. Results obtained from rooting experiment showed that the highest root number, root density and root quality were obtained using IBA at the concentration of 0.6 mg L-1, whereas the highest root length was observed by applying IBA at concentration of 0.3 mg L-1, which led to a significant difference with other treatments. Furthermore, results indicated that the effect of IBA on rooting of pepino microshoots was more than NAA.Conclusion: Generally, the best results were obtained by MS medium, 2 mg L-1 BA with 1 mg L-1 Kin for shoot proliferation, and IBA at concentration of 0.6 mg L-1 for the rooting of pepino nodal segments.