Developing plant regeneration systems for in vitro conservation of mandarin (Citrus reticulata) and pummelo (Citrus maxima).

摘要

Plant regeneration systems are being developed for micropropagation and in vitro conservation of the polyembryonic mandarin (Citrus reticulata) and monoembryonic pummelo (C. maxima). Mandarin seeds without seed coat germinated faster (in 7 d) and at higher frequency (100%) than intact seeds (33 d at 12-52%) in MB medium (MS-B5) basal medium with 1 mg benzylaminopurine [benzyladenine] (BAP)/litre. Cotyledonary node (CN) and shoot tip explants were excised from the seedlings and re-cultured onto fresh MB medium. CN explants either regenerated 3-5 shoots from each axillary bud 3 weeks after inoculation or somatic embryos were induced from the basal cut portion. Multiple shoots formed directly from the apical cut portion of the epicotyl sections closest to the shoot tips when cultured onto MB medium with 1-2 mg BAP/litre. Moreover, organogenic calluses were induced from the basal cut portion of all the epicotyl sections, which regenerated into shoots upon subculture in MG medium. Shoot tip explants also produced 30-40 shoots in MB medium (MS medium with 30 g sugar and 2 mg GA3/litre). Multiple shoots were also obtained from axillary buds of young shoots and seeds (from immature fruits) of indexed mandarin trees. In pummelo, somatic embryos were induced from albedo tissues of immature fruits cultured in MS and BP media with 1 mg/litre each of BAP and 2,4-D. Removal of these growth regulators allowed germination of the embryos and subsequent shoot growth. Organogenic calluses were observed using B5, MS and BP media with 0.5 mg 2,4-D/litre. After 3 months, shoots were regenerated. These regeneration systems are being utilized using virus-free materials for micropropagation, genetic transformation, slow growth and cryopreservation studies..