Callus induction, somatic embryogenesis and plant regeneration were obtaine
d in six different citrus species [Citrus deliciosa Ten. (cv 'Avana'), C.li
mon (L.) Burm. (cv 'Berna'), C.madurensis Lour. (cv 'CNR P9'), C.medica L.
(cv 'Cedro di Trabia'), C.tardiva Hort. ex Tan. (cv 'CNR P6'), C.sinensis (
L.) Osb. (cv 'Ugdulena 7')] from cultures of pistil transverse thin cell la
yer explants [(t)TCL]. Explants were cultured on three different media: the
nutrients and vitamins of Murashige and Skoog medium alone (MS) or MS supp
lemented with either 500 mg l(-1) malt extract (MS I) or 500 mg l(-1) malt
extract and 13.3 mu M 6-benzylaminopurine (MS II). Sucrose (146 mM) was use
d as the carbon source. Somatic embryos were visible 2-5 months after cultu
re initiation. The different genotypes showed a different embryogenic frequ
ency from stigma, style and ovary (t)TCL explants. All of the cultivars reg
enerated somatic embryos. Percentages of style (t)TCL explants producing so
matic embryos ranged from 0% (C.deliciosa, C.madurensis, C.sinensis and C.t
ardiva on the three different media) to 5.2% (C.limon on MS II). Embryo for
mation in stigma (t)TCL explants ranged from 0% (C.madurensis on MS and MS
I, C.sinensis on MS, C.deliciosa and C.tardiva on the three different media
) to 42.4% (C.limon on MS II). Embryo formation in ovary (t)TCL explants ra
nged from 0% (C.deliciosa on MS, C.limon, C.medica, and C.sinensis on the t
hree different media) to 9.3% (C.tardiva on MS I). After about 12 weeks som
atic embryos developed into plantlets at a high frequency.