Application of natural biostimulants in cactus in vitro cultures: evaluating the effectiveness of chitosan and nanosilicon

This study investigates the impact of chitosan (CH) and nanosilicon (nSi) on the micropropagation of two cactus species. Stem explants were cultured on Murashige and Skoog medium supplemented with chitosan at 20 - 60 mg L-1 or silicon nanoparticles at 100 - 500 mg L⁻¹. After 35 days of in vitro culture, morphological parameters were evaluated. Plantlets were acclimatised ex vitro to assess survival rates and root development. Chitosan significantly promoted shoot multiplication and root formation in both species, with optimal effects at moderate concentrations (40 mg L-1 for Echinopsis chamaecereus and 20 mg L-1 for Opuntia microdasys). In contrast, lower concentrations of nSi (100 or 200 mg L⁻¹) stimulated rhizogenesis in E. chamaecereus but had variable effects on O. microdasys. At 500 mg L⁻¹, nSi increased shoot biomass but reduced root growth. The survival and rooting rates during ex vitro acclimatisation were treatment- and concentration-dependent. These findings highlight the potential of CH and nSi as eco-friendly biostimulants in cactus micropropagation systems. Optimising their concentrations could enhance shoot and root development while reducing reliance on synthetic growth regulators.