Regeneration of Cucumis sativus var. sativus and C. sativus var. hardwickii, C. melo, and C. metuliferus from explants through somatic embryogenesis and organogenesis

Abstract

Regeneration in six inbred lines or F1 hybrids of Cucumis sativus was achieved on Murashige & Skoog's medium containing various concentrations of 2,4-D/BA, NAA/BA, NAA/Z or NAA/K. The range of regeneration frequency for cotyledon, leaf and petiole explants was 0–38, 0–75 and 14–96%, respectively, after 6–8 weeks in culture. Only one subculture of calli to growth regulator-free medium was required for regeneration. Preincubation of explants in the dark for 2–3 weeks was essential to achieve optimal regeneration. Highest frequency of plantlet formation occurred with petiole explants incubated on NAA/BA (5.0/2.5 μM), NAA/Z (5.0/5.0 μM) or 2,4-D/BA (5.0/5.0 μM). Approximately 80% of these plantlets survived after transplanting to greenhouse soil, and they flowered and set fruit. The F1 hybrid, Endeavor, gave the highest regeneration frequency of 91% on 2,4-D/BA at 5.0/5.0 μM. Formation of somatic embryos was observed on 2,4-D/BA, while organogenesis and embryogenesis both were evident on NAA/BA and NAA/Z. Cotyledonary explants yielded the lowest frequency (ca. 7%) of plantlet formation in this study. Plantlets of C. sativus var. hardwickii and an F1 hybrid of C. sativus x C. s. var hardwickii were regenerated on NAA/Z and NAA/K at frequencies of 15–65%, predominantly by the formation of somatic embryos. Shoots were obtained from cotyledon and leaf explants of C. metuliferus on IAA/BA (7.5/5.0 μM) and from leaf and petiole explants of C. melo on NAA/BA (5.0/2.5 μM), but plantlets were recovered only in C. melo.