Cobalt nanoparticles enhance the efficiency of in vitro propagation in purple passion fruit (Passiflora edulis Sims)

Abstract

In recent years, metallic nanoparticles have emerged as promising agents for improving plant tissue culture. This study aimed to evaluate the effects of cobalt nanoparticles (Co-NPs) at different concentrations on key stages of in vitro propagation in purple passion fruit (Passiflora edulis Sims), focusing on morphogenesis, shoot growth, rooting, and acclimatization. During the morphogenesis stage, thin cell layer explants cultured on medium supplemented with Co-NPs showed enhanced callus and shoot induction, with the highest rates at 0.3 mg L−¹. When combined with 1.5 mg L−1 BA, Co-NPs significantly increased the shoot induction rate (66.67%) compared to the control (51.11%). For shoot growth, Co-NPs alone at 0.3 mg L−1 significantly enhanced shoot height, leaf number, and SPAD index, while reducing ethylene accumulation and stress-related hormones. The combination of Co-NPs with 1.0 mg L−1 meta-Topolin further enhanced shoot growth and development. Endogenous hormone analysis revealed that Co-NPs modulated the levels and ratios of auxin, cytokinin, gibberellin, and abscisic acid, contributing to improved organogenesis and shoot growth. In the rooting stage, Co-NPs combined with 2.5 mg L−¹ IBA improved rooting rate (up to 86.67%), root number (5.33 roots/shoot), and reduced callus formation at the shoot base. In the acclimatization phase, plantlets derived from Co-NPs treatments, especially at 0.2 mg L−1, showed enhanced survival (97.78%), reduced defoliation, and vigorous growth. However, higher Co-NPs concentrations induced phytotoxic effects, including shoot tip necrosis. These findings suggest that Co-NPs, at optimized concentrations, could significantly enhance in vitro propagation efficiency and plantlet quality in purple passion fruit.