REGENERATION OF CUCUMIS-SATIVUS VAR SATIVUS AND CUCUMIS-SATIVUS VAR HARDWICKII, CUCUMIS-MELO, AND CUCUMIS-METULIFERUS FROM EXPLANTS THROUGH SOMATIC EMBRYOGENESIS AND ORGANOGENESIS - INFLUENCE OF EXPLANT SOURCE, GROWTH-REGULATOR REGIME AND GENOTYPE

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. © 1990 Kluwer Academic Publishers.