In vitro propagation of the Amazonian medicinal plant guayusa (Ilex guayusa) and effects of light in the growth and development of this shade tolerant plant

Guayusa (Ilex guayusa) is an endemic plant from the Amazon with potential medicinal applications. Indigenous people are familiar with such applications and use guayusa based on ancestral knowledge. There is a growing interest in guayusa-based products in urban areas of Ecuador and internationally. The supply cannot meet the demand. Currently, traditional practices are used for guayusa growth and the potential use of the protected forest is foreseen. This work describes a protocol for the in vitro propagation of guayusa, a sustainable solution to generate high quality plants in reduced space. Stakes obtained from stems were used as explants. Chemical sterilization with ethanol and sodium hypochlorite resulted in 100% surface-sterilized stakes. The growth medium mWPM resulted in favorable outcomes regarding shoot development and elongation, as well as rooting. Supplementation with activated charcoal resulted in reduced browning, only 10% of the shoots presented necrosis during the elongation phase. More than two thirds of shoots were able to develop roots spontaneously. Medium supplementation with the auxin indole-3-butyric acid, IBA, may be considered when rooting does not occur spontaneously. Acclimatization was performed in soil. The protocol was tested under different light spectra, revealing that guayusa growth is affected by light quality. The photobiology of this shade tolerant plant requires further characterization, but the data uncovered a potential role for green and far-red light in root development.