Optimizing the Duration of Acclimatization under Artificial Light for St. John's Wort Plantlets Grown Photoautotrophically and Photomixotrophically In Vitro

For production of high-quality St. John's wort (Hypericum perforatum L.) transplants, several authors have proposed in vitro multiplication of a superior germplasm by clonal propagation followed by ex vitro acclimatization in the greenhouse with natural light. This ex vitro acclimatization is a vital stage for successful transplant production. However, few studies have attempted to determine the optimum conditions for ex vitro acclimatization under artificial light. The objective of the current study was to find the necessary duration of ex vitro acclimatization by gradually reducing relative humidity under controlled environments with artificial light for St. John's wort plantlets grown photomixotrophically (sugar-containing medium) and photoautotrophically (sugar-free medium) in vitro. The results showed that all Photoautotrophically- and photo-mixotrophically-grown plantlets survived after the ex vitro acclimatization. Plantlets grown photoautotrophically in vitro were most suitable acclimatized to ex vitro environments by decreasing the relative humidity from 90 to 65% within two days. Meanwhile, the results suggested that plantlets grown photomixotrophically in vitro were most suitable acclimatized to ex vitro environments within four or seven days.