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Complex organic additives are known to improve growth and differentiation of in vitro plant cultures. The present investigation was conducted to determine the effect of various concentrations of yeast extract (YE) and casein hydrolysate (CH) on callus growth and somatic embryogenesis in date palm cultivar Nabout Saif. Callus induced from shoot tip explants was grown on callus multiplication medium supplemented with either YE or CH at 0.0, 0.1, 0.25, 0.5, and 1 g l−1. To induce somatic embryogenesis, callus was transferred to a hormone-free medium containing the corresponding concentration of additives. The results have shown that callus weight and the number of somatic embryos were directly proportional to increases in the concentration of organic additives tested. Callus growth was best achieved when 1 g l−1 of either YE or CH was added to the culture medium. At this concentration of YE, callus growth was double that of the control medium. On CH-containing media growth was 2.3 times that of the control. This indicates that CH is more effective in enhancing callus growth. However, YE was more effective in enhancing somatic embryogenesis. The data show that the best somatic embryo formation was obtained on either 1 g l−1 YE or 0.5 g l−1 CH which produced 45 and 30 embryos per culture, respectively, as compared to 20 embryos produced in the control treatment. Resultant somatic embryos successfully rooted and regenerated plantlets which exhibited normal growth in the greenhouse. Enhanced plant regeneration, an essential criterion for commercial micropropagation, was achieved.

Variability in callus growth and somatic embryogenesis in response to silver nitrate (AgNO3) among genotypes of date palm (Phoenix dactylifera L.) was investigated. Callus was cultured on MS medium containing 53.7 μM naphthaleneacetic acid (NAA) and 7.4 μM 2-isopentenyladenine (2iP) and supplemented with AgNO3 at 0, 12.5, 25, 37.5, 50, 62.5, 75, 87.5, or 100 μM. Subsequently, somatic embryogenesis was induced by transferring callus to hormone-free MS medium containing corresponding AgNO3 concentrations. Callus growth of cvs. Barhee, Naboot Saif, Ruzaiz, and Hillali was significantly promoted in response to 37.5 μM AgNO3 but optimum growth occurred at 50 μM in the former three cultivars, whereas cv. Hillali grew best at 62.5 μM. In contrast, cv. Khusab exhibited significant increase in callus weight at 12.5 μM but maximum growth occurred at 62.5 μM. Callus proliferation, expressed in increased callus fresh weight, which precedes the formation of somatic embryos during the regeneration stage, also varied depending upon AgNO3 concentration and cultivars. Regeneration percentage was significantly enhanced in all genotypes except cv. Hillali that was unaffected. Optimum AgNO3 concentrations were 62.5, 50, 37.5 μM for cvs. Barhee, Hillali, and Ruzaiz, respectively, whereas 12.5 μM was optimum for cvs. Naboot Saif and Khusab. Significant increase in number of somatic embryos was observed in cvs. Barhee, Naboot Saif, and Ruzaiz in response to 75, 12.5, and 37.5 μM AgNO3 but 75, 87.5, and 75 μM, respectively, were optimum. Embryo numbers in cvs. Hillali and Khusab were unchanged by AgNO3 and at concentrations higher than 50 μM numbers decreased. This study identified optimum AgNO3 levels for somatic embryo production of some commercial date palm cultivars.

Embryogenic callus derived from offshoot tip of date palm ( Phoenix dactylifera L.) was transferred to MS medium containing 0, 25, 50, 75, or 100 μM AgNO 3 combined with 0 or 0.5 μM 2iP. Embryogenic callus weight, number of embryos developed and embryo elongation were significantly influenced by the interaction between silver nitrate (AgNO 3 ) and 2iP. In the absence of 2iP, callus weight was greatest with 75 μM AgNO 3 , but in the presence of 2iP omitting silver nitrate resulted in the highest callus proliferation. The number of embryos increased in response to increasing silver nitrate concentration in the absence of 2iP, but in the presence of 2iP increasing the concentration of silver nitrate gave the opposite trend. The number of resultant embryos was the highest on 25 μM AgNO 3 in the presence of 0.5 μM 2iP. This treatment also caused maximum embryo elongation. The results have shown that silver nitrate promoted callus proliferation and enhanced the formation and elongation of somatic embryos of date palm. Furthermore, the action of silver nitrate was clearly modified by the addition of 2iP. Depending on the response, 2iP modification ranged from slight alteration to complete inversion of the general trend associated with increasing silver nitrate concentration. The observed stimulatory action of AgNO 3 on date palm somatic embryogenesis may contribute to improve existing regeneration systems particularly for recalcitrant date palm genotypes.

Shoots regenerated from leaf-derived callus of spinach (Spinacia oleracea L. cultivar ‘High Pack’) were induced to flower by exposure to 14-h photoperiods (50 μmol m−2 s−1) and day/night temperatures of 20° C 16° C . Leaves from male and female plants served as sources for explants. Shoots regenerated from callus were induced to flower on a hormone-free medium. The majority of regenerated plants exhibited sex corresponding to their respective explant donors; a proportion of regenerants of male origin, however, shifted to monoecious. These sex-modified plantlets developed viable seeds in vitro. This phenomenon can be useful in producing seeds from elite selected male plants.