Induction of highly embryogenic calli and plant regeneration in upland (Gossypium hirsutum L.) and pima (Gossypium barbadense L.) cottons

To accomplish our objective of broadening the number of regenerable cotton lines, we developed a protocol capable of producing plants through somatic embryogenesis of diverse cotton species. Callus was initiated from hypocoty l and cotyledon explants on a callus initiation medium [CIM; modified MS wi th I mg L-1 kinetin and 2 mg L-1 naphthaleneacetic acid (NAA)]. Friable emb ryogenic callus was periodically selected and transferred onto callus selec tion/maintenance medium (CS/MM) [modified MS with 0.1 mg L (1) kinetin and 0.5 mg L-1 NAA]. The selected callus was then transferred into a liquid emb ryo initiation medium (EIM) (modified MS medium in which NH4NO3 was removed and KNO3 amount doubled) followed by transfer to solid embryo maturation m edia EMMS2 (0.5 mg L-1 NAA + 0.05 mg L-1 kinetin). The liquid step not only decreased the culturing time but also increased the number of embryos per gram of cultured tissue. Germinating somatic embryos were placed on MS medi um with no hormones and plantlets were acclimatized before transfer to the greenhouse. Significant numbers of somatic embryos and their derived plantl ets were obtained from a commercial cultivar of G. hirsutum, Deltapine 90 a nd G. barbadense accession GB-35B126 (PI-528306). The mean embryos per gram for Deltapine 90 on EMMS2 were higher than those previously reported for C oker 312. Highly significant differences were found between the two genotyp es for both embryo and plant production. To our knowledge, this is the firs t report of regeneration of G. barbadense through somatic embryogenesis.