Micropropagation of Onion (Allium cepa L.) from Immature Inflorescences

Abstract

In vitro plant production by direct organogenesis from immature flower heads is an ideal approach for clonal propagation of onions (Allium cepa L.). This technique ensures genetic stability, high propagation rate, and maintains donor plant of explants with an advantage over other means of in vitro regeneration. Onion micropropagation is usually applied in breeding programs, maintenance, and multiplication of cytoplasmic-male sterile lines for hybrid production, germplasm conservation, and as a tool for the application of other biotechniques. For in vitro culture, mature onion bulbs are induced to reproductive phase by vernalization and forced to inflorescence initiation. Immature umbels are dissected from bulbs or cut directly when they appear from the pseudostem among the leaves. Disinfected inflorescences are cultivated in BDS basal medium supplemented with 30 g/L sucrose, 0.1 mg L naphtalene acetic acid, 1 mg/L N6 benzyladenine, and 8 g/L agar, pH 5.5, under 16 h photoperiod white fluorescent light (PPD : 50-70 umol /m2s) for 35 days. The regenerated shoot clumps are divided and subculture under the same condition. For bulbification phase, the individual shoots are cultured in BDS basal medium containing 90 g/L sucrose, without plant growth regulators, pH 5.5, under 16 h photoperiod. Microbulbs can be directly cultivated ex vitro without acclimation.