Abstract

Recent optimization of in vitro germination protocols for Colobanthus quitensis aimed at improving ex situ conservation prompted the exploration of complementary strategies to enhance seedling vigor and explant quality for micropropagation. Endophytic fungi release bioactive metabolites capable of modulating plant development, yet their application as live inoculants conflicts with aseptic tissue-culture workflows. To overcome this limitation, sterile culture filtrates (CFs) derived from endophytes associated with Araucaria araucana and C. quitensis were tested as potential biostimulants during early in vitro development. Seeds from three populations (Antarctic, sub-Antarctic and Andean) were surface-sterilized and pre-imbibed for 24 h in undiluted CFs from Umbelopsis sp., Trichoderma harzianum, or Hypocrea lixii. While CFs had no significant effect on germination outcomes across populations, they consistently modulated early seedling development in a population-specific way. In the Antarctic population, T. harzianum CF increased leaf number and size and promoted longer roots with greater area. In the sub-Antarctic population, all CFs elongated roots without increasing root area. In the Andean population, all CFs enhanced both root length and area. It is concluded that sterile CFs are compatible with axenic pipelines and can improve seedling, especially root system traits, without affecting germination, thereby increasing the availability and quality of explants for downstream micropropagation. Given population-specific responses, CF selection will likely require tailoring to seed origin, and future work should standardize CF preparation and include dose-response designs to support scalable application in ex situ propagation and conservation of C. quitensis.