Genotype-dependent in vitro response of date palm (Phoenix dactylifera L.) cultivars to silver nitrate

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 muM naphthaleneacetic acid (NAA) and 7.4 muM 2-isopentenyladenine (2iP) and supplemented with AgNO3 at 0, 12.5, 25, 37.5, 50, 62.5, 75, 87.5, or 100 muM. 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 muM AgNO3 but optimum growth occurred at 50 muM in the former three cultivars, whereas cv. Hillali grew best at 62.5 muM. In contrast, cv. Khusab exhibited significant increase in callus weight at 12.5 muM but maximum growth occurred at 62.5 muM. 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 muM for cvs. Barhee, Hillah, and Ruzaiz, respectively, whereas 12.5 muM 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 muM AgNO3 but 75, 87.5, and 75 muM, respectively, were optimum. Embryo numbers in cvs. Hillali and Khusab were unchanged by AgNO3 and at concentrations higher than 50 muM numbers decreased. This study identified optimum AgNO3 levels for somatic embryo production of some commercial date palm cultivars. (C) 2003 Elsevier B.V. All rights reserved.