Establishment of an Ex Vitro Rooting Strategy for Monochasma savatieri Increases Propagation Efficiency

Monochasma savatieri is an endangered hemiparasitic medicinal herb characterized by its broad host range. The ongoing decline of its natural resources highlights the urgent need for an efficient artificial propagation system. This study aimed to establish an optimized ex vitro rooting and acclimatization protocol through the assessment of plant growth regulators (PGRs), immersion durations, and substrate formulations. In vitro rooting on agar-solidified medium was suboptimal, thereby prompting the development of an ex vitro protocol. The major novelty of this work lies in the development of an integrated system that synergistically combines PGR pulse treatment with substrate physical property optimization, while completely eliminating the conventional in vitro agar-based rooting phase. Of the 18 PGR treatments screened, a 15 s immersion dip in NAA 480 mg·L^-1 + IAA 720 mg·L^-1 + GA 200 mg·L^-1 (treatment 10) performed best, achieving a 95.45% survival rate four months after transplantation, a 92.96% overwintering survival rate, and the longest roots (125.49 mm). Quadratic regression analysis revealed that root length is the best predictor of survival, with an optimum of 94.7 mm. Additionally, substrate evaluation revealed that T12 (peat moss:perlite:sawdust:carbonized chaff = 3:1:3:3, v/v) achieved the highest survival rate (85.20%), which correlated with moderate aeration porosity (17.44%), high water-holding porosity (142.56%) and the highest total porosity (160.00%). The integrated protocol eliminates the in vitro rooting phase, thereby reducing both cost and labor while shortening the production cycle by at least one month. Collectively, this study establishes a complete and efficient ex vitro rooting acclimatization system for M. savatieri, providing a practical basis that may facilitate large-scale propagation and conservation of this threatened species.