Abstract
Variability in callus growth and somatic embryogenesis in response to silver nitrate (AgNO
3) 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 AgNO
3 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 AgNO
3 concentrations. Callus growth of cvs. Barhee, Naboot Saif, Ruzaiz, and Hillali was significantly promoted in response to 37.5
μM AgNO
3 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 AgNO
3 concentration and cultivars. Regeneration percentage was significantly enhanced in all genotypes except cv. Hillali that was unaffected. Optimum AgNO
3 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 AgNO
3 but 75, 87.5, and 75
μM, respectively, were optimum. Embryo numbers in cvs. Hillali and Khusab were unchanged by AgNO
3 and at concentrations higher than 50
μM numbers decreased. This study identified optimum AgNO
3 levels for somatic embryo production of some commercial date palm cultivars.