Seed Morphometry and Viability Assessment of Dendrobium gibsonii Paxton by the double-staining technique

Abstract

Dendrobium gibsonii is an epiphytic ornamental orchid native to Southeast Asia, including Northeast India, with significant conservation value but with inadequate information on seed biology. We examined seed morphometry using light and scanning electron microscopy and measured seed and embryo length, width, volumes, seed length and width (SL/SW), embryo length and width (EL/EW) ratios, and seed volume-to-embryo volume ratio (SV/EV). Viability and permeability were also assessed after scarification with 0.5, 1.5, 3.0, and 5.0% NaOCl for 5, 10, 15, and 30 min (5 mg seeds per treatment), followed by TTC and Trypan Blue staining. The interaction between NaOCl concentrations and time was highly significant for both permeability and viability (all p < 0.001). Tukey tests indicated that 3% and 5% produced the higher permeability increases (notably at 15–30 min), whereas 1.5–3% for 10–15 min (3%×10 min = 93.81 ±1.25% viability) was optimal for viability; prolonged 5% exposure was toxic. Morphometry revealed minute, dust-like, fusiform seeds with a prolate-spheroid embryo and <50% air space, implying reduced buoyancy and limited dispersal. These traits are taxonomically informative. Future work should expand morphometric comparisons across other Dendrobium species to determine species-versus genus-specific indicators, perform controlled buoyancy and storage trials, validate TTC outcomes via in vitro germination, and evaluate gentler scarification methods (enzymatic, mechanical, sonication) to enhance permeability without compromising viability, thereby facilitating propagation and conservation strategies.