In vitro plant regeneration of spinach from mature seed-derived callus

Summary A system for the regeneration of spinach (Spinacia oleracea L.) from mature dry seed explants has been established. The response of two commercial spinach cultivars, ‘Grandstand’ and ‘Baker’, was examined. Callus proliferation was most prominent on MS medium supplemented with 9.3 μM of 6-furfurylaminopurine (kinetin) and 3.39 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Adventitious shoot formation was observed within 8 wk after callus was transferred onto regeneration medium. Shoot regeneration was best from callus induced on 9.3 μM kinetin and 4.56 μM 2,4-D. The regeneration medium contained 9.3 μM kinetin, 0.045 μM 2,4-D, and 2.89 μM gibberellic acid (GA₃). Shoots were rooted on hormone-free medium, and plants grown in a greenhouse showed normal phenotype. This system is beneficial in rapid propagation of spinach plants, particularly when only a limited number of seeds are available.     

Efficient plant regeneration from embryogenic suspension cultures of sweetpotato

Summary Using 15 Chinese and Japanese cultivars of sweetpotato, Ipomoea batatas (L.) Lam., we succeeded in developing an efficient plant regeneration system from embryogenic suspension cultures. The embryogenic callus derived from shoot apices of the 15 cultivars was used to initiate embryogenic suspension cultures in Murashige and Skoog (MS) medium containing 9.05 μM 2,4-dichlorophenoxyacetic acid (2,4-D). Rapidly proliferating and well-dispersed embryogenic suspension cultures were established. Cell aggregates 0.7–1.1 mm in size from embryogenic suspension cultures were transferred to solid MS medium supplemented with 9.05 μM of 2,4-D and formed embryogenic callus with somatic embryos. The embryogenic callus with somatic embryos was further transferred to MS medium supplemented with 3.78 μM of abscisic acid, resulting in the germination of somatic embryos. Within 20 wk after the initiation, the frequencies of cell aggregates forming plantlets reached approximately 100% for the 15 tested cultivars. These plantlets, when transferred to soil, showed 100% survival. No morphological variations were observed.     

Callus induction and plant regeneration of U.S. rice genotypes as affected by medium constituents

Summary This study was conducted to establish and optimize a regeneration system for adapted U.S. rice genotypes including three commercial rice cultivars (LaGrue, Katy, and Alan) and two Arkansas breeding lines. Factors evaluated in the study were genotype, sugar type, and phytohormone concentration. The system consisted of two phases, callus induction and plant regeneration. In the callus induction phase, mature caryopses were cultured on MS medium containing either 1% sucrose combined with 3% sorbitol or 4% sucrose alone, and 0.5 to 4 mg·L⁻¹ (2.26 to 18.10 μM) 2,4-D with or without 0.5mg·L⁻¹) (2.32 μM) kinetin. In the plant regeneration phase, callus was transferred to 2,4-D-free MS medium containing 0 or 2 mg·L⁻¹ (9.29 μM) kinetin combined with 0 or 0.1 mg·L⁻¹ (0.54 μM) NAA. Callus induction commenced within a week, independent of the treatments. Callus growth and plant regeneration, however, were significantly influenced by interactions among experimental factors. Generally, the greatest callus growth and plant regeneration were obtained with 0.5 mg·L⁻¹ (2.26 μM) 2,4-D and decreased with increasing 2,4-D concentrations. Kinetin enhanced callus growth only when combined with 0.5 mg·L⁻¹ (2.26 μM) 2,4-D, and 4% sucrose. Inducing callus on kinetin-containing medium generally enhanced regeneration capacity in the presence of sucrose but not with a sucrose/sorbitol combination. Media containing sucrose alone generally supported more callus proliferation, but the sucrose/sorbitol combination improved regeneration of some cultivars. NAA and kinetin had little effect on regeneration.     

Embryogenic callus induction and plant regeneration media for bentgrasses and annual bluegrass

Summary Embryogenic callus induction and plant regeneration systems have long been established for creeping bentgrass (Agrostis palustris Huds.), but little research has been reported on optimal medium for embryogenic callus induction and plant regeneration in velvet bentgrass (Agrostis canina L.), colonial bentgrass (Agrostis capillaries L.), and annual bluegrass (Poa annua L.). The present study compared 14 callus induction media and eight regeneration media for their efficacies on embryogenic callus induction and plant regeneration in these four species. The embryogenic callus initiation media contained the Murashige and Skoog inorganic salts and vitamins supplemented with 2,4-dichlorophenoxyacetic acid or 3,6-dichloro-anisic acid and 6-benzyladenine. l-Proline or casein hydrolyzate was included in some media to stimulate embryogenic callus formation and plant regeneration. The frequencies of embryogenic callus formation ranged from 0% to 38% and exhibited medium differences within each of the four species. Callus induction media, plant regeneration media, and genotypes affected plant regeneration rates, which varied between 0% and 100%. The embryogenic callus induced on Murashige and Skoog medium supplemented with 500 mgl⁻¹ casein hydrolyzate, 6.63 mg l⁻¹ (30 μM) 3,6-dichloro-anisic acid and 0.5–2.0 mg l⁻¹ (2–9 μM) 6-benzyladenine had much higher regeneration rates than those formed on other callus induction media. Embryogenic callus of annual bluegrass had higher regeneration rates than those of bentgrass species. MSA2D, a media containing 2 mgl⁻¹ (8 μM) 2,4-dichlorophenoxyacetic acid, 100 mgl⁻¹ myo-inositol, and 150 mgl⁻¹ asparagine, was effective in promoting embryogenic callus formation in creeping bentgrass but not in colonial and velvet bentgrasses and annual bluegrass.     

Highly efficient embryogenesis and plant regeneration of tall fescue (Festuca arundinacea Schreb.) from mature seed-derived calli

Summary We report a protocol for efficient plant regeneration of four tall fescue (Festuca arundinacea Schreb.) cultivars (‘Surpro’, ‘Coronado’, ‘Summer Lawn’, and ‘Fawn’) via somatic embryogenesis. Calli were initiated from mature seeds grown on modified Murashige and Skoog (MMS) medium supplemented with 7.0mgl⁻¹ (31.7μM) 2,4-dichlorophenoxyacetic acid (2,4-D) and 0.05 mgl⁻¹ (0.23 μM) kinetin (Kin). Calli were maintained and proliferated by subculture at monthly intervals on MMS medium containing 4.5 mgl⁻¹ (20.4 μM) 2,4-D and 0.2mgl⁻¹ (0.9 μM) Kin. Somatic embryos (SE) were induced from seed-derived calli on SE-induction medium (MMS supplemented with 2.0 mgl⁻¹ 2,4-D and 0.2mgl⁻¹ Kin). Plantlets were regenerated from somatic embryogenic calli grown on modified SH medium supplemented with 2 mgl⁻¹ Kin. Using this optimized protocol, 78.6–82.3% of mature seeds of all four cultivars produced SE clusters, of which 93.5–95.3% regenerated into plants within 10 wk. The regenerants showed no phenotypic abnormalities.     

Thidiazuron stimulates shoot regeneration of sugarcane embryogenic callus

Summary Efficient shoot regeneration of sugarcane (Saccharum spp. hybrid cv. CP84-1198) from embryogenic callus cultures has been obtained using thidiazuron (TDZ). Callus was placed on modified Murashige and Skoog (MS) medium containing 2.3 μM 2,4-dichlorophenoxyacetic acid (2,4-D), or 9.3 μM kinetin and 22.3 μM naphthaleneacetic acid (NAA) and compared with the same MS medium supplemented with 0.5, 1.0, 2.5, 5.0 or 10.0 μMTDZ, A11 TDZ treatments resulted in faster shoot regeneration than the kinetin/NAA treatment, and more shoot production than either the 2,4-D or kinetin/NAA treatments. Maximum response, as determined by total number of shoots (26 per explant) and number of shoots greater than 1 cm (4 per explant) 4 wk after initiation, was obtained with 1.0 μM TDZ. The shoots rooted efficiently on MS medium supplemented with 19.7 μM indole-3-butyric acid (IBA). These results indicate that TDZ effectively stimulates sugarcane plant regeneration from embryogenic callus, and may be suitable to use in genetic transformation studies to enhance regeneration of transgenic plants.     

Plant regeneration of Agave tequilana by indirect organogenesis

Summary Indirect organogenesis was developed in Agave tequilana. Leaf segments and meristematic tissue from the central head (‘pi?a’) were evaluated as explant sources. A minimal-sized explant with high bud-forming capacity (19.5 BFC) was obtained through a cross section of meristematic tissue from in vitro plantlets. In callus culture, the best growth response was due to naphthalene acetic-acid (NAA) presenting a contrasting response compared to 2,4-dichlorophenoxyacetic acid (2,4-D). Regeneration from meristem segments and callus was obtained using 1.1 μM 2,4-D and 44 μM 6-benzylaminopurine (BA). The regeneration capacity of callus was maintained for 3 mo. Shoots regenerated were rooted in a hormone-free MSI medium and acclimatized in a greenhouse with a 100% survival.     

Overcoming phenolic accumulation during callus induction and in vitro organogenesis in water chestnut (Trapa japonica Flerov)

Summary Procedures for callus induction and subsequent organogenesis in the aquatic plant, water chestnut (Trapa japonica Flerov), were established. Phenolics exuded from explants at the callus-induction stage adversely affect callus growth. For cotyledonary node-derived callus cultured in Murashige and Skoog (MS) medium (full, half or quarter strength) containing 2,4-dichlorophenoxyacetic acid (2,4-D) alone or in combination with benzyladenine (BA), the accumulation of phenolics was reduced and callus induction increased by the addition of 10.8 μM phloroglucinol (PG) to the medium. Ascorbic acid was also effective in reducing phenolic accumulation, but less effective for callus induction than PG. Half-strength MS medium supplemented with 2.7 μM 2,4-D, 108.0 μM casein hydrolyzate, and 10.8 μM PG supported maximum callus induction. Plant organogenesis was increased by addition of vitamins (0.27 μM biotin and 2.7 μM folic acid) to half-strength MS medium supplemented with 0.27 μM BA. Many shoots developed from the regenerated nodal shoot explants in liquid half-strength MS salts medium supplemented with 1.08 μM BA and 0.27 μM naphthaleneacetic acid. Individual shoots were excised and cultured in liquid half-strength MS medium supplemented with 5.4 μM IBA and rooted plantlets (108) were transferred and acclimatized in plastic pots. After 3 wk, the plantlets were transplanted in a water chestnut field and the survival rate was 100%.     

<Emphasis Type="Italic">In vitro</Emphasis> propagation of the rare medicinal plant <Emphasis Type="Italic">Ceropegia candelabrum</Emphasis> L. through somatic embryogenesis

Summary Efficient in vitro propagation of Ceropegia candelabrum L. (Asclepidaceae) through somatic embryogenesis was established. Somatic embryogenesis depended on the type of plant growth regulators in the callus-inducing medium. Friable callus, developed from leaf and internode explants grown on Murashige and Skoog (MS) medium supplemented with 4.52μM2,4-dichlorophenoxyacetic acid (2,4-D), underwent somatic embryogenesis. Compared to solid media, suspension culture was superior and gave rise to a higher number of somatic embryos. Transfer of the friable callus developed on MS medium containing 4.52μM 2,4-D to suspension cultures of half- or quarter-strength MS medium with lower levels of 2,4-D (0.23 or 0.45 μM) induced the highest number of somatic embryos, which developed up to the torpedo stage. Somatic embryogenesis was asynchronous with the dominance of globular embryos. About 100 mg of callus induced more than 500 embryos. Upon transfer to quarter-strength MS agar medium without growth regulators, 50% of the somatic embryos underwent maturation and developed into plantlets. Plantlets acclimatized under field conditions with 90% survival.     

Somatic embryogenesis and plant regeneration of turf-type bermudagrass: Effect of 6-benzyladenine in callus induction medium

In order to optimize tissue culture conditions for bermudagrass, an important warm-season turfgrass species, tissue culture responses of young inflorescences of a hybrid bermudagrass cultivar `Tifgreen' (Cynodon dactylon×Cynodon transvaalensis) and a common bermudagrass cultivar `Savannah' (Cynodon dactylon) were investigated. When cultured on Murashige and Skoog medium with 4.52 to 13.57 μM (1–3 mg l^-1) 2,4-D, young inflorescence segments yielded non-embryogenic calli which were unorganized and had loosely associated, long tubular cells on the surface. However, inclusion of 6-benzyladenine (BA) in callus induction medium at a level of 0.044 μM (0.01 mg l^-1) induced formation of a compact, nodular embryogenic structure on approximately 20% of the calli. Calli with such a compact embryogenic structure were highly regenerable. When young inflorescences smaller than 0.75 cm were cultured, the embryogenic structure yielded green plantlets with regeneration rates of 79.5% and 83.3%, respectively for the two cultivars. All 96 plants regenerated from calli induced in the BA-containing medium were green and morphologically normal. The embryogenic nature of the compact structure was confirmed by scanning electron microscopy. This revised version was published online in June 2006 with corrections to the Cover Date.     

Induction of somatic embryogenesis in cashewnut (Anacardium occidentale L.)

Summary Somatic embryogenesis was induced in callus cultures derived from nucellar tissue of cashewnut (Anacardium occidentale L.). Callus was obtained from nucellar tissue after 3 wk of culture on semisolid Murashige and Skoog (MS) basal medium supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D, 5 μM)+gibberellic acid (GA₃, 15 μM)+N⁶-benzyladenine (BA, 5 μM). This callus gave rise to an embryogenic mass after 9 wk on maintenance medium containing 2,4-D (10 μM)+GA₃ (15 μM)+4% sucrose +0.5% activated charcoal +10% coconut water (CW) +0.05% casein hydrolysate (CH). The embryogenic mass, after transfer to medium supplemented with 2,4-D (5 μM)+GA₃ (30 μM)+4% sucrose +0.5% activated charcoal +10% CW +0.05% CH, gave rise to somatic embryos. The developmental stages of somatic embryos were observed using light and stereo microscopes. Histological study of somatic embryo development was also carried out. The present study would be useful for clonal propagation, and variety improvement in cashewnut, which is essential due to its increasing demand and export potential.     

Simple one-medium formulation regeneration of fingerroot [<Emphasis Type="Italic">Boesenbergia rotunda</Emphasis> (L.) mansf. Kulturpfl.] via somatic embryogenesis

Summary Most published protocols necessitate different media formulations for multistep somatic embryogenesis. This study aims to establish a simple but effective formulation for the regeneration of plantlets of the pharmaceutically active Boesenbergia rotunda (L.) Mansf. Kulturpfl, formerly Boesenbergia/Kaempferia pandurata (Schult), to ensure a superior and consistent supply of materials for commercialization purposes. In this study, a single-medium formulation of Murashige and Skoog (MS) supplemented with 13.54μM 2,4-dichlorophenoxyacetic acid (2,4-D) was found to be the only medium out of eight formulations to promote the complete somatic embryogenesis process for the culture of B. rotunda (L.). Callus cultures were initiated from a total of 280 explants of rhizome meristem. The percentage of cultures forming embryogenic callus was 23.3 ±4.3% on this MS medium augmented by 13.54μM 2,4-D. The best plantlet regeneration rate was attained from the first subcultured callus with a mean of 6.6±0.1 plantlets per 1 cm diameter aggregate of callus. Somatic embryogenesis characteristic of monocots was evident from histological studies. The regenerated plantlets have been successfully established in soil.     

Callus formation and plant regeneration from tubercles of Coryphantha elephantidens (Lem.) Lem.

Summary Callus cultures were established from pith tissue of Coryphantha elephantidens (Lem.) Lem. on Murashige and Skoog (MS) basal medium supplemented with 9.05 μM 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.3 μM kinetin. Highest shoot regeneration frequency was observed on a medium containing 6.9 μM kinetin and 2.3 μM 2,4-D under 30 μE m⁻² s⁻¹ light intensity with a 16-h photoperiod. Calluses retained organogenic potential throughout several passages of subculture (18 mo.). Shoots were rooted on MS medium without plant growth regulators. All (100%) plantlets transplanted to soil survived acclimatization. Regenerated plants showed good overall growth and were morphologically similar to the mother plants.     

Somatic embryogenesis in <Emphasis Type="Italic">Schisandra chinensis</Emphasis> (Turcz.) Baill.

Summary Regeneration of plants via somatic embryogenesis was achieved from zygotic embryo explants isolated from mature seeds of Schisandra chinensis. Merkle and Sommer's medium, fortified with 2,4-dichlorophenoxyacetic acid (2,4-D; 9.04 μM) and zeatin (0.09 μM), was effective for induction of embryogenic callus. The development of a proembryogenic mass and somatic embryos occurred on Murashige and Skoog medium (MS) free of plant growth regulators. The embryogenic callus induced on Merkle and Sommer's medium supplemented with 2,4-D (9.04 μM) and zeatin (0.09 μM) showed development of the maximum number of somatic embryos when transferred to MS medium free of plant growth regulators. The maximum maturation and germination of cotyledonary somatic embryos (46.3%) occurred on MS medium supplemented with 2,4-D (0.45 μM) and N⁶-benzyladenine (1.11 μM). The somatic embryo-derived plants were successfully hardned, with a survival rate of approximately 67%, and established in the field.     

High-frequency plant regeneration from coleoptile tissue of indica rice (Oryza sativa L.)

Summary An efficient method was established for high-frequency embryogenic callus induction and plant regeneration from 3-,4-, 5- and 7-d-old coleoptile segments of Indica rice (Oryza sativa L. cv. Kasturi), Compact and friable callus developed from the cut ends and also on the entire length of the coleoptile segments cultured on Murashige and Skoog (MS) basal medium (1962) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D, 4.50–18.0 μM), kinetin (2.32 μM) and sucrose (3%, w/v). High frequency embryogenic callus induction and somatic embryo development was achieved when embryogenic calluses were transferred to MS medium supplemented with 2.25 μM 2,4-D, 2.32 μM kinetin, 490 μM L-tryptophan and 3% (w/v) sucrose. Plant regeneration was achieved by transferring clumps of embryogenic callus onto MS medium containing 2.85 μM indole-3-acetic acid (IAA), 17.77 μM 6-benzylaminopurine (BA) and 3% (w/v) sucrose. Histological observations of embryogenic calluses revealed the presence of somatic embryos and also plant regeneration via multiple shoot bud formation. Three, 4- and 5-d-old coleoptile segments showed a significantly (P<0.05) higher frequency of plant regeneration and mean number of plantlets per explant in comparison to 7-d-old coleoptile segments. The highest frequency (73.5%) of plant regeneration and mean number of plantlets (11.9±1.0) was obtained from 4-d-old coleoptile segments. Regenerated shoots were rooted on MS basal medium containing 4.92 μM indole-3-butyric acid (IBA) and plants were successfully transferred to soil and grown to maturity.     

Efficient plant regeneration in <Emphasis Type="Italic">Holarrhena antidysenterica</Emphasis> Wall., from shoot segment-derived callus

Summary A procedure has been outlined for plant regeneration of an important medicinal shrub, Holarrhena antidysenterica, through shoot segment-derived callus. Explants used for callus induction were shoot segments derived from 14-d-old axenic plants on Murashige and Skoog (MS) medium supplemented with 15 μM N⁶-benzyladenine (BA). A white friable type of callus was obtained in 4.52 μM 2,4-dichlorophenoxyacetic acid and 2.32 μM kinetin which did not have the potentiality to regenerate. High-frequency shoot differentiation was achieved on transferring the friable callus to MS medium supplemented with 17.8 μM BA and 8.0 μM naphthaleneacetic acid. The highest percentage of calluses forming shoots (65.06±2.26) was achieved in this medium. The organogenetic potential of the regenerating callus was influenced by the age of the culture. Rooting was achieved on the shoots using MS medium with 25 μM indolebutyric acid. The plantlets were acclimatized and established in soil. The regenerated plants were morphologically uniform and exhibited similar growth characteristics and vegetative morphology to the donor plants.     

Somatic embryogenesis,encapsulation, and plant regeneration of <Emphasis Type="Italic">Rotula aquatica</Emphasis> lour., a rare rhoeophytic woody medicinal plant

Summary Indirect somatic embryogenesis, encapsulation, and plant regeneration was achieved with the rare rhoeophytic woody medicinal plant Rotula aquatica Lour. (Boraginaceae). Friable callus developed from leaf and internode explants on Murashige and Skoog (MS) medium with 0.45 μM 2,4-dichlorophenoxyacetic, acid (2,4-D) was most effective for the induction of somatic embryos. Subculture of the callus onto half-strength MS medium with the same concentration of 2,4-D resulted in highly embryogenic callus. Suspension culture was superior to solid medium culture for somatic embryogenesis. Embryogenic callus.during subsequent transfer to suspension cultures of half-strength MS medium having 0.23 μM 2,4-D induced the highest number of somatic embryos (a mean of 25.6 embryos per 100 mg callus) and the embryos were grown up to the torpedo stage. Transfer of embryos to half-strength MS basal solid medium allowed development, of 50% of the embryos to the cotyledonary stage. Of the cotyledonary embryos, 90% underwent conversion to plantlets on the same medium. Encapsulated cotyledonary embryos exhibited 100% conversion to plantlets. Ninety-five percent of the plantlets established in field conditions survived, and were morphologically identical to the mother plant.     

Regeneration from long-term embryogenic callus of the <Emphasis Type="Italic">Rosa hybrida</Emphasis> cultivar kardinal

Summary Media components used for three stages of development: (1) callus maintenance, (2) maturation of embryos, and (3) conversion of embryos to plants were shown to affect regeneration of plants for the commercially important red rose cultivar Kardinal. Embryogenic callus was maintained for 5yr on either Schenk and Hildebrandt’s basal salts medium (SH) supplemented with 13.6 μM 2,4-dichlorophenoxyacetic acid (2,4-D) or Murashige and Skoog’s basal salts medium (MS) supplemented with 18.1 μM dicamba and 0.46 μM kinetin. Maturation of embryos was three times higher using callus maintained on the SH medium supplemented with 2,4-D while conversion of cotyledonary-stage embryos to plants was significantly higher (10 times) using callus that had been maintained on MS medium with dicamba and kinetin. Maximum maturation (13.5%), and conversion (15.2%), occurred when callus was cultured on MS maturation medium without hormones. Cotyledonary-stage embryos cultured on MS conversion medium supplemented with abscisic acid (5–20 μM) produced plants that survived at a significantly higher rate (two times) in the greenhouse than when embryos were cultured without abscisic acid. The highest rate of plant regeneration occurred when embryogenic callus of ‘Kardinal’ was maintained on MS medium supplemented with dicamba and kinetin, maturation of embryos occurred on MS maturation medium without hormones, and conversion of cotyledonary-stage embryos occurred on MS conversion medium supplemented with abscisic acid.     

Somatic embryogenesis and plant regeneration in centipedegrass (Eremochloa ophiuroides [Munro] Hack.)

Centipedegrass (Eremochloa ophiuroides [Munro] Hack.) is an important warm-season turfgrass and pasture grass. To explore the potential use of biotechnical tools in breeding of centipedegrass, we established an efficient plant regeneration system for this species. Four basal media and 24 combinations of 2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzyladenine (BAP) were examined for their effects on callus induction from mature seed explants. Twenty combinations of naphthaleneacetic acid (NAA) and BAP were tested for their effect on plant regeneration. Results indicated that Murashige and Skoog basal medium supplemented with 4.5 mg l⁻¹ 2,4-D and 1 mg l⁻¹ BAP was the best medium for callus induction, while the combination of 2 mg l⁻¹ BAP and 1 mg l⁻¹ NAA induced the highest rate of regeneration and development of shoots and roots. This work provides a basis for the breeding of centipedegrass through somaclonal variation and genetic transformation.     

Somatic embryogenesis and plant regeneration from floral explants of cacao (Theobroma cacao L.) using thidiazuron

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.