Effect of zeatin and casein hydrolysate on in vitro asymbiotic germination of immature seeds of Vanilla planifolia Jacks ex Andrews (Orchidaceae)

Abstract

The germination of Vanilla planifolia seeds under natural environmental conditions is very low (0.1 %) because of specific mycorrhizal requirements. Therefore, the species is typically propagated spending vegetative using stem cuttings. Thus, all cultivated plants are genetically identical and susceptible to multiple abiotic and biotic stressors. Artificial propagation from seeds is difficult for most terrestrial orchids native to temperate regions, and V. planifolia is no exception. As propagation from the seeds of this species has low success rates, in this study, an effective reproducible protocol for the in vitro asymbiotic germination of Vanilla planifolia seeds was established. For this purpose, the effects of three asymbiotic culture media on seed germination and seedling development of Vanilla planifolia [Murashige and Skoog (MS), Vacin and Went (VW), Knudson ‘C’ (KC)] were tested, two zeatin concentrations (Z = 0.25 and 0.50 mg L−1), two concentrations of casein hydrolysate (CH=50 and 500 mg L−1), and two combinations of these (Z = 0.25 mg L−1 + CH=250 mg L−1) and (Z = 0.50 mg L−1 + CH=500 mg L−1). The highest germination rate (74.5%) was recorded for the treatment with MS salts at a quarter strength supplemented with 500 mg L−1 of CH. All the seeds that germinated under this treatment showed high survival and vigorous seedling growth. In contrast, in the treatment with MS salts at a quarter strength supplemented with combination of CH and Z (CH=500 mg L−1 + Z = 0.50 mg L−1) resulted in the production of calluses (53 %).