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The regeneration potential of shoot tip, stem, leaf, cotyledon and root explants of two papaya cultivars (Carica papaya cv. 'Solo' and cv. 'Sunrise') were studed. Callus induction of these two cultivars of papaya showed that the shoot tips and stems are most suitable for forming callus, while leaves, cotyledons and roots are comparatively difficult to induce callus. Callus induction also varied with the varities. Somatic embryogenesis was obtained from 3-month-old root cultures. A medium containing half strength of MS inorganic salts, 160 mg/l adenine sulfate, 1.0 mg/1 NAA, 0.5 mg/1 kinetin and 1.0 mg/1 GA3 was optimal for embryogenesis. The callus maintained high regenerative capacity after two years of culture on this medium. Plants derived from somatic embryos were obtained under green-house conditions.

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SUMMARYEmbryogenically competent callus was induced from in vitro grown Saccharum officinarum L. (NCo 310) plantlets by plating young leaf segments on MS basal medium supplemented with 30 /iM dicamba for 21 d in darkness, and subsequently transferring to a medium (EFDM) on which embryos could form and develop. Embryogenic response was improved if the EFDM was supplemented with 1 or 5 fiM. dicamba, casein hydrolysate (1 g 1"'), and 6 % maltose or 6-9 % corn syrup. Calli maintained their embryogenic competence for up to 16 months under these conditions, and with alternate weekly subcultures on to fresh media containing 20 fiM and 30 fiM dicamba in the dark, embryogenic callus proliferation could be further increased. Additional improvements in embryogenic competence were optimized to over 40 months when primary callus was alternately precultured at weekly intervals either witb 10"^ M ABA or S % sorbitol and then transferred to a medium containing 20 or 30 /iM dicamba during maintenance. In general, medium plant growth regulator and nutritional cues, especially dicamba concentration, maltose/corn syrup levels and ABA/sorbito\ preconditioning, were observed to influence critically both embryogenic callus proliferation and the frequency of somatic embryogenesis. The data are discussed within the context that these treatments can be successfully manipulated to enhance long-term embryogenic competence and high-frequency somatic embryogenesis in sugarcane.Key words: Saccharum officinarum (sugarcane), abscisic acid, corn syrup, dicamba, embryogenic competence, maltose.some as yet unknown physiological factors, long-INTRODUCTION term retention of embryogenic competence in most There are currently many reports of somatic embr>'o-grass cell and tissue culture systems has proved to be genesis in callus cultures of the major species of quite difficult (VasU, 1987). Gramineae. In these crops the phenomenon of As part of our continuing investigation of somatic somatic embryogenesis holds useful promise for embr>'o differentiation in Saccharum officinarum L., breeding purposes, particularly with respect to cell we report here on a series of experiments, the fusion, the stable introduction of foreign genetic purpose of which was to evaluate the influence of information, and tolerance to salt and herbicides, various medium components and culture conditions. Additionally, mass in vitro production of somatic which could be manipulated to enhance long-term embryos in bioreactors and the subsequent pro-retention of embryogenic competence and highduction of synthetic seeds with characteristically frequency initiation and development of somatic superior (or desirable) qualities to in situ seeds, can embryos in this species, only be achieved if efficient culture conditions are fully developed for long-term, high-frequency ^^.^ERIALS AND METHODS optimization of high-quality somatic embryos with ^^^^^^ induction and culture conditions reliable regenerative competence. Thus far, however, because of the arbitrary nature of media recipes and ...

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