Optimization of direct organogenesis from immature inflorescence explants of coconut (Cocos nucifera L.)

The mass propagation of elite, high-yielding coconut palms is a primary objective of many coconut improvement programs, as it enables the clonal multiplication of disease-resistant genotypes with superior productivity and other valuable agronomic traits. The present study aimed to establish a protocol for direct organogenesis from immature inflorescences, bypassing an intermediary callus phase, to minimize the risk of somaclonal variation among regenerated plantlets. Immature inflorescences were collected from 25-30-year-old West Coast Tall palms. Those with an outer spathe length of 2-12 cm were selected, and rachillae segments 1.0 mm long were excised and cultivated under dark conditions on three culture initiation media (WPM, Y3, and MS) containing various plant growth regulator combinations. After eight months of culture, WPM supplemented with 5 mg L⁻¹ TDZ proved most effective for culture initiation, yielding the highest number of vegetative buds and the least amount of tissue browning. The greatest number of multiple shoots and the most pronounced shoot elongation were achieved on WPM medium containing NAA (1 mg L⁻¹), BAP (1 mg L⁻¹), and TDZ (5 mg L⁻¹). Subsequent shoot elongation was further optimized on Y3 medium supplemented with NAA (2 mg L⁻¹) and BAP (5 mg L⁻¹), which also promoted the maximum number of leaves. For rooting, a reduction in the basal salt concentration of the medium, combined with the addition of NAA and IBA, proved to be the most effective treatment. Rooted plantlets were successfully hardened under controlled conditions before being acclimatized in a greenhouse. Genetic fidelity assessment using SSR marker analysis confirmed a high level of genetic uniformity between the regenerated plantlets and their respective mother palms. This protocol describes a reliable and efficient method for producing true-to-type, healthy, and high-yielding coconut plants, particularly for tall cultivars and hybrids. It offers significant potential for the large-scale commercial propagation and conservation of elite coconut germplasm.