Repression of asexual embryogenesis in vitro by some plant growth regulators.

A factor that represses asexual embryogenesis has been observed in the Rutaceae, with particularly high concentrations in the naturally monoembryonic cultivars. This investigation was an initial step towards identifying the factor. Citrus reticulata Blanco Ponkan mandarin nucellus explants and Daucus carota L. 'Queen Anne's Lace' callus were employed to examine effects of known plant growth regulators and to determine possible identity of one or more of them with the repressive factor. The chalazal halves of ovules of C. media L. 'Citron of Commerce' were used as control repressor source. Embryo initiation and growth of both test tissues were depressed markedly by 2,4-D, abscisic acid and ethephon. Slight inhibitions were obtained with IAA, kinetin and gibberellic acid. Recovery from the repressor did not occur readily in Citrus nucellus following recultures in citron-ovule-free medium; carrot callus resumed normal embryogenesis immediately upon transfer to suppressor-free medium. The repression by natural sources apparently involved the combined action of some or all natural hormones that are generically related to the above.