SOMATIC EMBRYOGENESIS AND PLANT-REGENERATION FROM IMMATURE AND MATUREEMBRYOS OF TROPICAL AND SUBTROPICAL ZEA-MAYS L GENOTYPES

Ten maize inbred lines, with tropical and subtropical origin have been evaluated for their ability to form callus from which plants can be r egenerated. Callus cultures were derived from immature and mature embr yos. By culturing immature embryos, embryogenic callus was obtained fr om 7 lines, and plants regenerated from 5 of these. Dicamba was signif icantly superior to 2,4-D both for stimulating and maintaining embryog enic calli. Callus cultures could not be maintained on media containin g 2,4-D for periods longer than three months. Long term regenerable cu lture on a medium supplemented with dicamba was achieved for two lines : CML67 and CML137. Callus embryogenesis was related to callus shape a nd area. Mitotic analysis of 172 plants regenerated from 5 lines indic ated that they had karyotypes indistinguishable from those of their pa rents. Immature hybrid embryos derived from crosses between recalcitra nt and Type I embryogenic lines produced Type I embryogenic calli. It is concluded that on the media tested the formation of Type I callus b ehaves like a dominant trait. By culturing mature embryos, embryogenic callus was obtained from 2 out of 4 lines and plants mere regenerated . The frequency of callus induction ranged from 20 to 59% and the embr yogenic callus frequency from 0 to 7.8%. Dicamba was superior to 2,4-D in promoting callus induction and embryogenesis. Regenerated plants h ad the normal chromosome number (2n=20) and the chromosomes the same C -banding pattern as in the parental lines.