Micropropagation of a Bulgarian Local Form of Prunus mahaleb L. in Agar-Solidified Culture and PlantFormTM TIS Bioreactor

Prunus mahaleb L. is an important cherry rootstock because of its tolerance to drought and poor soils. Despite its horticultural importance, efficient in vitro multiplication of P. mahaleb remains challenging. Therefore, this study compared conventional agar-solidified culture with the PlantFormTM temporary immersion system (TIS) for micropropagation of a Bulgarian local form of P. mahaleb. Three basal media, Murashige and Skoog (MS), Woody Plant Medium (WPM), and Driver and Kuniyuki Walnut (DKW), were initially evaluated in both cultivation systems. The media were subsequently supplemented with ascorbic and citric acids to determine whether these antioxidants could further improve culture performance. Compared with agar-solidified culture, the PlantFormTM TIS significantly enhanced explant proliferation, achieving the highest number of new shoots (6.69 ± 1.82) and biomass production on antioxidant-supplemented DKW medium. The same treatment also resulted in the greatest accumulation of photosynthetic pigments, with maximum total chlorophyll (0.991 ± 0.025 mg g−1 FW) and carotenoid (0.349 ± 0.050 mg g−1 FW) contents. Rooting efficiency ranged from 38.89% to 51.85% and did not differ significantly among treatments, whereas acclimatization was not achieved under the conditions tested. These findings demonstrate that PlantFormTM TIS combined with antioxidant-supplemented DKW medium provides a promising approach for the multiplication of this P. mahaleb form. However, the rooting and acclimatization stages require further optimization.