In vitro culture of orchid plantlets within conventional photomixotrophic micropropagation (PMM) systems (sucrose containing media in a non-enriched CO2 environment) often induces vigorous growth and multiplication. However, transition to ex vitro conditions frequently results in significant plantlet loss during the acclimatization process. Recent studies investigating micropropagation within photoautotrophic (PAM) systems (sucrose-free media in enriched CO2 conditions) have demonstrated improved plantlet survival during the acclimatization period due to greater root growth and stomata adaptation. Laelia purpurata var. alba, an orchid with many endangered relatives, was chosen as a model orchid species to investigate if plantlet culture within PAM in vitro systems has the potential to improve propagation success and ex vitro survival of endangered Laelia species. Protocorm-like bodies with developed two fully extended leaves were transferred into PMM (photosynthetic photon flux 50 μmol·m-2·s-1 under non-enriched CO2 conditions) and PAM (photosynthetic photon flux 150 μmol·m-2·s-1, CO2 level enriched to 1500 μmol·mol-1) systems. After 6 weeks, plantlet rooting within the PMM system was variable and inconsistent, while all PAM plantlets produced healthy robust root systems. Average fresh weights and percent shoot development were not significantly different between treatments. Induction of improved root growth by PAM systems may improve orchid plantlet survival rates during acclimatization and advance our ability to increase endangered orchid populations.
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