SOMATIC EMBRYOGENESIS AND PLANT REGENERATION FROM IMMATURE HICKORY (CARYA CATHAYENSIS SARG.) EMBRYOS

In hickory, plant regeneration in tissue culture usually takes place through adventitious shoots, which are difficult to root. Somatic embryogenesis, if successful, would improve the efficiency of mass propagation. We attempted to induce somatic embryos from immature embryos. The effect of PGRs and duration of explant culture on somatic embryogenesis were studied. A histocytological study of differentiation of embryogenesis was also conducted. Woody Plant Medium (WPM) was supplemented with PGRs, 2% glucose and was solidified with 0.8% agar type A. The results showed that 73% of explants produced embryogenic callus when cultured on 1.0 mg l(-1) BA, 0.001 mg l(-1) picloram, and 1.0 g l(-1) CH. This medium was also the best for direct somatic embryogenesis, with a frequency of 70%. The highest frequency (29%) of somatic embryogenesis from embryogenic callus was obtained in the combination of 1.0 mg l(-1) BA, 0.01 mg l(-1) picloram, and 0.5 g l(-1) CH. The optimal conditioning medium duration for somatic embryogenesis was 4 weeks. The greatest frequency (52%) of somatic embryos germination was obtained on WPM medium supplemented with 0.1 mg l(-1) BA and 0.01 mg l(-1) IBA after 8-week culture. Histocytological studies indicated that somatic embryos go through globular, heart-shaped torpedo and cotyledonary embryo phase. However, the synchronization was poor and various phases of embryo development could be observed simultaneously.