High frequency somatic embryogenesis and plant regeneration of an elite Chinese cotton variety

An elite Chinese cotton (Gossypium hirsutum L.) cultivar Simian-3 was chosen for tissue culture. Callus with a high frequency of somatic embryogenesis, somatic embryos, and regenerative plants was obtained. Callus was induced from three types of explants on MSB (MS salts with B, vitamins) medium supplemented with zeatin (ZT) only, but the percentage of callus induction and growth of callus varied. It appeared that it was much easier to induce callus from hypocotyl than cotyledon or root explants. The concentrations of ZT were critical to the induction and proliferation of callus. The optimum ZT concentration for callus induction was 3.0~5.0mg/L. Two kinds of callus could be identified after 70 days of culture: embryogenic and nonembryogenic callus. Embryogenic callus developed into somatic embryos at various stages after 20 days of subculture. The capability of embryogenesis depended on the explant types. The root was the most responsive explant for production of somatic embryos, the hypocotyl was the next, and the cotyledon was the last. Moreover, a low concentration of ZT was advantageous to the induction of embryogenic callus. 2, 4-dichlorophenoxyacetic acid (2, 4-D) promoted the proliferation of embryogenic callus, but had a negative effect on the differentiation and germination of somatic embryos. Addition of activated charcoal or a proper combination of ZT and 3-indoleacetic acid (IAA) could promote the production, maturation and germination of somatic embryos. The best medium for the proliferation of embryogenic callus was ZH medium (Zhang et al., 1996) with 1.0mg/L 2, 4-D, 0.5mg/L kinetin (KT) and 0.5mg/L ZT. The best medium for the differentiation and germination of somatic embryos was MSB with 0.1mg/L ZT and 2g/L activated charcoal. An efficient protocol for the production of high frequency somatic embryogenesis and plant regeneration of an elite cotton variety Simian-3 has been developed. Complete plants could be regenerated through somatic embryogenesis from hypocotyl, cotyledon and root explants in 3-4 months.