Regulation of in vitro development of pitaya through culture medium, zinc and light quality: morphoanatomical and physiological characteristics

Abstract

Pitaya micropropagation constitutes an important strategy for the production of genetically uniform, vigorous, and pathogen-free seedlings. However, the success of in vitro cultivation depends on factors such as the consistency of the culture medium, the spectral quality of light, and the availability of micronutrients, which directly influence plant growth and morphophysiological quality. This study aimed to evaluate the in vitro development of Selenicereus undatus (Haw.) D. R. Hunt and Hylocereus polyrhizus (Salm-Dyck) R. Bauer (Cactaceae), investigating the effects of culture medium consistency, LED light spectral quality, zinc concentrations, and the mineral composition of MS and PC-L2 media on plant growth, physiology, and nutritional composition. Experiments were conducted using different agar concentrations (0.0, 3.5, 7.0, 10.5, and 14.0 g L⁻¹), four LED spectral qualities (white, blue, purple, and red), and two zinc concentrations (8.60 and 17.20 mg L⁻¹). Biometric traits, photosynthetic pigments, chlorophyll a fluorescence parameters, nutritional composition, and anatomical characteristics of shoots and root systems were evaluated. The reduction of the physical restriction imposed by the culture medium, particularly in agar-free systems, promoted greater linear growth and higher biomass accumulation in the plants, whereas higher agar concentrations favored chlorophyll accumulation. The spectral quality of light showed speciesspecific effects, with white and purple light promoting better biometric performance and greater biomass accumulation. Anatomical changes were also observed, including an increase in vascular bundle density under conditions of higher zinc availability. In general, Selenicereus undatus showed greater growth and vegetative vigor, whereas Hylocereus polyrhizus exhibited higher accumulation of photosynthetic pigments under certain spectral light conditions. The composition of the culture medium significantly influenced plant performance, with the PC-L2 medium promoting greater shoot elongation, higher biomass accumulation, and improved root development in S. undatus. Potassium was the predominant element in plant tissues in all treatments, whereas magnesium, phosphorus, and zinc showed variations depending on species, treatments, and culture medium. It is concluded that the integrated regulation of culture medium consistency, LED spectral light quality, zinc availability, and mineral composition of the medium is essential for optimizing the growth and morphophysiological quality of pitayas cultivated in vitro. The use of agar-free systems, associated with white or purple LED light and the PC-L2 medium, represents a promising strategy for improving micropropagation protocols and for producing seedlings with greater vigor and higher potential for ex vitro acclimatization. Keywords: cactaceae; Hylocereus polyrhizus; LED light; micropropagation; physical matrix; Selenicereus undatus.