SOMATIC EMBRYOGENESIS AND PLANTLET REGENERATION FROM IMMATURE AND MATURE TISSUES OF SWEETGUM (LIQUIDAMBAR STYRACIFLUA)

Source tree, explant developmental stage and plant growth regulator tr eatments were tested for their relationship to induction of somatic em bryogenesis from different explanted tissues of sweetgum (Liquidambar styraciflua), a common hardwood tree of the southern US. Induction of indirect somatic embryogenesis from staminate inflorescence explants w as related to all three independent variables. The highest induction f requencies were obtained from the least elongated inflorescences cultu red on medium with 0.01 or 0.1 mg/l thidiazuron. While inflorescence e xplants from eight of nine source trees yielded embryogenic cultures, two trees were the source of the majority of the embryogenic cultures. Conversely, induction of direct somatic embryogenesis from seed expla nts was only related to fruit collection week, an index of explant dev elopmental stage, with more immature seeds giving a higher frequency o f induction than mature seeds. Culture on medium with 0.5 mg/l or 3 mg /l 2,4-D induced embryogenesis from seed explants. Proembryogenic mass es (PEMs) derived from inflorescence tissues and seed tissues produced somatic embryos when transferred to basal medium supplemented with ac tivated charcoal. Germination and conversion frequencies of the somati c embryos were not related to cold pretreatment. Germination frequency , which ranged as high as 90%, varied significantly among clones, whil e conversion frequency, with a maximum of 60%, did not. (C) 1998 Elsev ier Science Ireland Ltd. All rights reserved.