Further characterization of somatic embryogenesis and plantlet regeneration in pecan (Carya illinoensis)

The effects of cultivar, sampling date, tree-source of explants, and duration on conditioning medium on somatic embryogenesis in pecan (Carya illinoensis) were examined. Zygotic embryos were collected from cultivars 'Stuart' and 'Desirable' 12-18 weeks post-pollination, cultured for 1 or 3 weeks on a woody plant medium (WPM) for conditioning supplemented with 2 mg/l2,4-dichlorophenoxyacetic acid (2,4-D) and 0.25 mg/l benzylaminopurine (BAP), then transferred to basal WPM for embryo induction. Somatic embryos became visible as early as 2 weeks following transfer to a hormone-free medium. Embryogenic response after 10 weeks on basal medium varied significantly between cultivars and among sampling dates within cultivars. Immature zygotic embryos collected in a developmental stage of rapid cotyledon expansion 15 weeks post-pollination gave the highest embryogenic response, which was 54.7% in 'Desirable' and 85.2% in 'Stuart' after 10 weeks on basal medium. There was no significant effect of duration on conditioning medium on embryogenic response in either cultivar. The effect of different trees as explant sources was not significant in 'Stuart' but was significant in 'Desirable'. Conversion of somatic embryos to plantlets hase been obtained in limited numbers following desiccation treatments and transfer of embryos to light.