Somatic embryogenesis and plant regeneration from pistil thin cell layers of Citrus

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.