Somatic embryogenesis and plant regeneration from floral explants of cacao (Theobroma cacao L.) using thidiazuron |
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Authors: | Zhijian Li Abdoulaye Traore Siela Maximova Mark J Guiltinan |
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Institution: | (1) Department of Horticulture, College of Agricultural Sciences, The Pennsylvania State University, 103 Tyson Building, 16802-4200 University Park, Pennsylvania |
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Abstract: | Summary A procedure for the regeneration of cacao (Theobroma cacao) plants from staminode explants via somatic embryogenesis was developed. Rapidly growing calli were induced by culturing
staminode explants on a DKW salts-based primary callus growth (PCG) medium supplemented with 20 g glucose per L, 9 μM 2,4-D, and thidiazuron (TDZ) at various concentrations. Calli were subcultured onto a WPM salts-based secondary callus growth
medium supplemented with 20 g glucose per L, 9 μM 2,4-D, and 1.4 nM kinetin. Somatic embryos were formed from embryogenic calli following transfer to a hormone-free DKW salts-based embryo development
medium containing sucrose. The concentration of TDZ used in PCG medium significantly affected the rate of callus growth, the
frequency of embryogenesis, and the number of somatic embryos produced from each responsive explant. A TDZ concentration of
22.7 nM was found to be the optimal concentration for effective induction of somatic embryos from various cacao genotypes. Using
this procedure, we recovered somatic embryos from all 19 tested cacao genotypes, representing three major genetic group types.
However, among these genotypes, a wide range of variation was observed in both the frequency of embryogenesis, which ranged
from 1 to 100%, and the average number of somatic embryos produced from each responsive explant, which ranged from 2 to 46.
Two types of somatic embryos were identified on the basis of their visual appearance and growth behavior. A large number of
cacao plants have been regenerated from somatic embryos and established in soil in a greenhouse. Plants showed morphological
and growth characteristics similar to those of seed-derived plants. The described procedure may allow for the practical use
of somatic embryogenesis for clonal propagation of elite cacao clones and other applications that require the production of
a large number of plants from limited source materials. |
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Keywords: | somatic embryogenesis cocoa Theobroma cacao plant regeneration thidiazuron |
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