The critically endangered orchid Dendrobium officinale, valued for its medicinal properties, depends on specific seedling-associated mycorrhizal fungi (SAMF) for successful early-stage seedling development. However, conservation efforts are often hindered by difficulties in obtaining suitable SAMF, leading to poor seedling establishment in both natural and cultivated environments. In this study, we explored the growth-promoting effects of SAMF and evaluated the performances of synthetic fungal combinations. Our results demonstrated that mycorrhizal fungi, widely distributed across multiple habitats with high isolation frequencies, significantly promoted the growth of D. officinale, with specific fungi favoring different growth parameters. Tulasnella sp. TP-2 and TP-3 significantly improved stem diameter and plant height by 2.622 mm and 4.621 cm, while Tulasnella sp. TP-8 significantly increased tillering by a factor of 4.47. Additionally, Tulasnella sp. TP-11 and TP-13 markedly increased the number of new leaves (4.45) and new roots (2.688), respectively, identifying them as essential core OMFs for D. officinale seedlings. Contrary to expectations, synthetic fungal combinations composed of core orchid mycorrhizal fungi (core OMFs) did not exhibit synergistic growth-promoting effects. Instead, pronounced offset effects were observed, indicating that interactions between fungi may introduce competition or inhibition, limiting their collective ability to enhance plant growth. Our results confirmed that the core OMFs significantly promoted the growth of D. officinale seedlings. These core OMFs can serve as essential components in specialized microbial fertilizers for D. officinale, improving growth efficiency and yield, and supporting the sustainable development of the D. officinale industry.

Malania oleifera Chun & S.K. Lee, an endemic monotypic species that belongs to the family Olacaceae, is under continuous pressure of decline owing to several ecological and physiological factors. The present study aimed to establish an efficient in vitro protocol for callus-mediated indirect somatic embryogenesis in M. oleifera by alleviating tissue browning. Internodes and leaves obtained from seedlings were used as explants. Antioxidant pre-treatment (ascorbic acid, AA) followed by different carbon sources (sucrose, maltose, glucose, and fructose) and plant growth regulators in various concentrations and combinations were employed in Woody Plant Medium (WPM) to alleviate explant browning and induce callus formation from the explants. AA pre-treatment and subsequent culture on maltose at a concentration of 116.8 mM were optimal for controlling phenolic exudation on >90% of both explants. The highest responses of 53.77% and 57.43% for embryogenic calli were induced from internode and leaf explants, respectively. The highest responses, 85.22% and 93.80%, were observed for somatic embryos that matured into the globular, heart-shaped and torpedo stages at different percentages on NAA 2.5 mg/L in combination with BA 1.0 mg/L for both explants. The matured somatic embryos were finally germinated at a maximum concentration of GA₃, 2.0 mg/L. All plantlets were successfully hardened and acclimatized under culture room conditions and then transferred to the greenhouse. The current study suggests an efficient protocol for indirect somatic embryogenesis by alleviating phenolic exudation from the explants of M. oleifera. This first successful report of in vitro culture establishment in M. oleifera may offer an effective alternative measure to conserve this species and provide a system for analyzing bioactive chemicals and for use in the oil industry.