Direct shoot regeneration via organogenesis in chiehqua (Benincasa hispida Cogn. var. Chieh-qua How)

Abstract

A plant regeneration system was established from cotyledon explants of chieh-qua (Benincasa hispida Cogn. var. Chieh-qua How). To obtain optimal conditions of adventitious shoot induction, the cotyledon explants were excised from seedlings of different genotypes as well as seed germination conditions, and then cultured on media containing different concentrations of 6-benzylaminopurine (6-BA)/1-naphthaleneactic acid (NAA). Among the eight genotypes, the highest rate of shoot regeneration was obtained from the cotyledons of inbred line A39. The adaxial portion of cotyledons of seedlings cultured for 3 days in darkness and 1 day in light was the appropriate explants for adventitious shoot organogenesis. The highest frequency of adventitious shoot organogenesis (52.2%) and mean number of shoots per explant (4.2) were achieved on Murashige and Skoog (MS) medium supplemented with 6 mg l^-1 6-BA and 0.2 mg l^-1 NAA. Adventitious shoots were observed to regenerate directly from cotyledons rather than from calli. A medium supplemented with AgNO₃ was not beneficial for shoot induction. Adventitious shoots were elongated in MS medium supplemented with 3 mg l^-1 6-BA and 0.2 mg l^-1 NAA. Elongated shoots were rooted in ½ MS medium with 0.5 mg l^-1 indole-3-acetic acid (IAA). Regenerated plantlets were transferred to a greenhouse for about 1 month, and subsequently transplanted into an open field.

Keywords: Benincasa hispida, chieh-qua, adventitious shoot, genotypes, plant regeneration.