Plant regeneration through direct somatic embryogenesis on seed coat explants of cashew ( Anacardium occidentale L.)

Abstract

A protocol of plant regeneration through direct somatic embryogenesis was established for the first time on cashew using seed coat explants. Frequency of embryogenesis was significantly influenced by type and age of the explant and growth regulators supplemented to the medium. Seed coats isolated from the immature nuts between 15 and 40 days after pollination were superior in the induction of somatic embryos. Only 35% of seed coat halves induced somatic embryos. Somatic embryos developed best on MS medium fortified with 13.3 μM benzyladenine (BA), 271.5 μM adenine sulphate (Ads) and 2.7 μM naphthaleneacetic acid (NAA). On this medium, an average of 3.3 embryos were developed per half seed coat. Embryos originated from the inner layer of the seed coat. Transfer of the embryos to fresh induction medium facilitated development of secondary somatic embryogenesis (more than 10 embryos per primary embryo). Embryos exhibited all stages of development, i.e. from globular to cotyledonary. Fifty percent of the embryos underwent conversion upon transfer to MS medium containing 4.65 μM kinetin and plantlets were successfully transferred to field conditions. Ninety percent survived in field conditions.