Colorimetric Evaluation of Callus with Embryogenic Potential and Biomass Accumulation in the Woody Medicinal Plant Polyalthia bullata Suspension Culture

Abstract

Identifying embryogenic callus in plant tissue culture, particularly in woody species, such as Polyalthia bullata, is often hindered by its morphological similarity to non-embryogenic callus. This study introduced a rapid, cost-effective colorimetric method using the triphenyl tetrazolium chloride (TTC) assay to evaluate embryogenic callus induction in P. bullata via cell suspension culture. Suspension cultures were established using 30 µM dicamba in combination with varying concentrations of thidiazuron (TDZ: 2 to 10 µM). Among the treatments, 30 µM dicamba with 8 µM TDZ induced the highest biomass and a distinct yellowish green callus morphology, typically associated with embryogenic potential. The TTC assay confirmed high cell viability, with red staining indicating elevated metabolic activity in embryogenic cultures. These findings validate the TTC assay as an efficient proxy for embryogenic callus detection, providing a valuable alternative to labor-intensive histological or molecular methods. This approach enhances tissue culture protocols for this woody medicinal plant, supporting its large-scale propagation, biomass productivity, and conservation.