Invitro germination and optimization of basal media for protocorm-like bodies proliferation in Dieniaophrydis(J. Koenig) Seidenf

Abstract

Dienia ophrydis is an endangered terrestrial orchid used for its ornamental and therapeutic purposes. This orchid possesses an anti-malarial alkaloid known as Malaxin. There is ongoing exploitation in the wild due to illegitimate herbal collection and climate change. To control the potential risk of extinction, there are no conservational measures or in vitro protocols established in this genus. The study focuses on addressing a germination protocol and enhancement of protocorm-like bodies (PLB) proliferation by optimizing the basal media and vitamins. It also aims to improve the misinterpretation of tetrazolium viability results in orchid testa along with a permeability test. Further, the seeds were subjected to 1% TTC staining to perform embryo viability test and 0.4% trypan blue (TB) dye for testa permeability. Ten basal media such as Gamborg's medium, Mitra medium, Thomale GD medium, Vacin and Went medium, Knudson C medium, Knop's medium, MS medium and ½ MS medium, ¼ MS medium, and modified MS medium (MMS) were tested for seed germination. The Half-strength MS medium responded with 92% of the highest germination and T-GD medium is not suitable for seed germination. The seed viability and permeability result showed 93% of permeability, 72% viability, and 9% dead seeds. Protocorms were transferred to the modified mMS medium containing half-strength macronutrients, full micronutrients, and 10 ppm of thiamine in vitamin formulation. PLB proliferation was observed and 12 shoots emerged from a single protocorm explant. Subsequently, the seedlings were acclimatized with 8-0-24 ratios of nitrogen, phosphorus, and potassium (NPK) as determined by soil testing. The study contributes in experimenting with seed germination of terrestrial orchid seeds asymbiotically and to establishing a protocol for conservation programs, especially in this genus.