In vitro micropropagation of the ornamental prickly pear cactus Opuntia lanigera Salm–Dyck and effects of sprayed GA3 after transplantation to ex vitro conditions

We established the conditions to micropropagate the ornamental prickly pear cactus Opuntia lanigera Salm–Dyck through axillary shoot development from isolated areoles. For the shoot proliferation stage different explant orientation (vertical and horizontal), type of cytokinin (BA, DAP and K), and concentrations (0, 1.25, 2,5, 5.0 and 7.5 mg/L) were evaluated. Media Murashige, T., Skoog, F., 1962. A revised medium for rapid growth and bioassays with tobacco cultures. Phys. Plant. 15, 473–497: 50 and 100%], and carbohydrate concentration (0.25, 0.5, 0.75 and 1.0%) were studied to optimize individual shoot growth and elongation. Following micropropagation and plantlet acclimatization, the effects of GA₃ on plant growth were determined by spraying a series of increasing concentrations (0, 150, 300 and 450 ppm). A reliable and efficient protocol of micropropagation was established for this particular plant species. The greatest propagation ratio (shoot proliferation) was obtained when explants were cultured in vertical orientation (4.975 shoots per explant) as compared to horizontal position (3.692 shoots per explant). The addition of BA to the media resulted in increased shoot number per explant (8) in comparison to K and DA, which produced only 2 shoots in average. However, after 42 days of culture, significantly higher shoot length was obtained with DAP (14 mm) compared to K and BA (4 mm). After the shoot proliferation stage, an elongation subculture was performed prior rooting in which shoot growth was enhanced when crowns of shoots were cultured in 50% of basal salt formulation of Murashige and Skoog (1962) and low sucrose concentration (2.5 and 5%). Exogenous application of GA₃ after plantlet acclimatization on glasshouse conditions increased spine-hair (developed from areoles in young plants) length as part of short-term effects. However, significantly higher values were obtained in plantlets treated with 300 ppm of GA₃ when compared with the rest of the treatments. At the end of the study, the most important long-term effect produced by GA₃ was the suppression of total shoot growth. The micropropagation protocol described here and the conditions to grow the plants through fertigation plus the application of GA₃ that induced changes in the phenotype may be used in commercial exploitations to regenerate 12,500 plantelts in average after 12 months of culture and produce healthy plants with better ornamental characteristics and higher commercial value.