Regeneration of Cucumis sativus var. sativus and C. sativus var. hardwickii, C. melo, and C. metuliferus from explants through somatic embryogenesis and organogenesis Influence of explant source, growth regulator regime and genotype Abstract Regeneration in six inbred lines or F~ 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 #M), NAA/Z (5.0/5.0#M) or 2,4-D/BA (5.0/5.0/~M). Approximately 80% of these plantlets survived after transplanting to greenhouse soil, and they flowered and set fruit. The F~ hybrid, Endeavor, gave the highest regeneration frequency of 91% on 2,4-D/BA at 5.0/5.0 #M. 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 F~ 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. me'tuliferus on IAA/BA (7.5•5.0 ~tM) and from leaf and petiole explants of C. melo on NAA/BA (5.0/2.5/~M), but plantlets were recovered only in C. melo.Abbreviations: BA-benzyladenine; 2,4-D-2,4-dichlorophenoxy-acetic acid; IAA-indoleacetic acid; Kkinetin; MS-Murashige & Skoog's medium; NAA-naphthaleneacetic acid; Z-zeatindihydroside ethanol for 20s, soaked for 10-12min in 7.5% commercial bleach, and rinsed three times in sterile distilled water prior to use.

Haploid induction has potential application for maize breeding. This paper reports that maize haploid plants have been induced by in vitro culture of pollinated ovaries. From a total of 26,400 cultured ovaries, 24 haploid plants were obtained and two of them were doubled after colchicine treatment. The maximum frequency of gynogenesis was 0.17% at 19.5 h post-pollination (HPP). The results showed that HPP was an important factor affecting plant induction from ovaries. Regenerated diploid R 0 plants were then subjected to genetic analysis using SSR molecular markers. One R 0 plant, whose progeny revealed a high level of homogeneity for several agro-morphological traits, was homozygous at 20 loci tested, with 11 showing paternal and 9 maternal banding pattern. This demonstrates that it is feasible to induce maize haploid plants by in vitro culture of pollinated ovaries.

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