Optimization of photoperiod and immersion frequency in an IoT-integrated Temporary Immersion System for enhanced growth and reduced contamination of Coelogyne pandurata culture

Abstract The integration of Internet of Things (IoT) technology into a Temporary Immersion System (TIS) was studied for micropropagation of the endangered black orchid, Coelogyne pandurata . The study aimed to optimize photoperiod and immersion frequency to enhance growth and reduce contamination. Plantlets were subjected to four photoperiods (12, 16, 20, and 24 h) and three immersion frequencies (4, 6, and 8 times/day for 2 min each) in a completely randomized factorial design. Contamination control improved from 100% in the preliminary trial to about 10% in the final phase through multi-stage sterilization and equipment modification. Growth data were collected only after modifications were fully implemented. The optimal treatment was continuous illumination (24 h light) with lower immersion frequency (four immersions/day), yielding the highest shoot multiplication (4.98 shoots per explant) and favorable biomass accumulation with minimal hyperhydricity. Statistical analysis confirmed photoperiod and immersion frequency significantly affected shoot number, root length, and fresh weight, with no significant interaction. Shorter photoperiods (12 h light) promoted root elongation, while moderate photoperiods (12–16 h light) enhanced chlorophyll and carotenoid accumulation. Principal Component Analysis (PCA) showed PC1 (41.0% variance) contrasted shoot proliferation with hyperhydricity and root elongation, and PC2 (20.4% variance) was linked to leaf greenness. The PCA biplot indicated extended photoperiods with moderate immersion clustered together, showing consistent growth responses. The IoT-integrated TIS provides a controlled, automated platform for C. pandurata micropropagation at the laboratory scale, supporting ex situ conservation efforts for this endangered orchid.