Table 3.
Cytokinin applications in mass propagation of major horticultural fruit species through somatic embryogenesis.
| Species | Cultivar/Accession | Source of Explants | Factor/s Investigated | Major Outcomes | Reference |
|---|---|---|---|---|---|
| Papaya Carica papaya L. |
Maradol Roja | Immature zygotic embryos (hermaphrodite flowers) | Effect of culture conditions on the germination of somatic embryos: RITA® temporary immersion system. ½ MS + vitamins + BAP + GA3 |
Optimum inoculum density of 200 mg fresh mass of somatic embryos produced 95% germination of somatic embryos | [135] |
| Sweet orange Citrus sinensis (L.) Osbeck |
Washington Navel | Pistils from flower buds (20-year-old plants) | Effect of BAP, NAA, and 2,4-D on somatic embryo induction and conversion into plantlets. MS medium + Nitsch and Nitsch vitamins |
Induction of embryogenic calli; germination of somatic embryos into plantlets; in vitro grafting | [136] |
| Sweet orange Citrus sinensis Osbeck.) | Tobias | Pistils from flower buds (5-year-old plants) | Effect of BAP, NAA, and 2,4-D on somatic embryo induction and conversion into plantlets. WPM, N6 medium |
Induction of embryogenic calli; germination of somatic embryos into plantlets; in vitro grafting | [137] |
| Litchi Litchi chinensis Sonn. |
Brewster; Mauritius | Leaves of new flushes of mature (>100-year-old) trees |
Induction of embryogenic cultures from leaves of mature trees. B5 Gamborg salts + MS vitamins + 2,4-D + BA, KIN, Z |
Induction of embryogenic cultures, maturation of somatic embryos, recovery of plants, and greenhouse acclimatization of plants | [138] |
| Litchi Litchi chinensis Sonn. |
Xiafanzhi | Immature zygotic embryos | Isolation of protoplasts from embryogenic suspensions and formation of somatic embryos from protoplasts. MS salts + B5 Gamborg vitamins + KIN + NAA (SE development); KIN + GA₃ (conversion to plantlets) |
Development of somatic embryos from protoplast-derived proembryos and their regeneration to plantlets | [139] |
| Apple Malus × domestica Borkh. |
Golden delicious | Cotyledons of immature zygotic embryos | Effect of PGR combination on somatic embryogenesis. MS + combinations of PGRs: BAP, KIN, NAA, and IBA |
Induction of embryogenic masses (18%); conversion of somatic embryos to regenerants (30%) | [83] |
| Apple Malus × domestica Borkh. |
‘Gloster 69’ | Cotyledon-derived cultures of immature zygotic enmbryos |
Influence of different PGR combinations on secondary somatic embryogenesis. MS + combinations of PGRs: NAA, IBA, 2,4-D, KIN, and BAP or with TDZ |
Optimum SSE (>73%) culture of large size solrtatic embryos or cotyledon-like structures on medium containing a combination of NAA/BAP/KIN or TDZ (10 btM) alone |
[140] |
| Banana Musa spp. |
Grand Naine (AAA); Tropical (AAAB) | Immature male flowers | Effect of BAP and NAA on the induction of somatic embryos. MS medium + glutamine (0–200 mg/L) |
Induction of embryogenic cultures in cell suspension culture; somatic embryo formation and conversion to plantlets | [141] |
| Banana Musa spp. |
Chenichampa (AAB) | Immature female flower bud | Effect of 5 different MS medium on the induction of somatic embryos MS 1–5 contained PGRs (IAA, TDZ, NAA, Z, 2iP, BAP), biotin, L- ascorbic acid |
MS-3 (0.10 mg/L NAA, 0.3 mg/L Z, 0.14 mgl/ 2iP) supplemented with CH:Gln (100:150 mg/L) increased somatic embryo formation tenfold relative to the control | [142] |
| Passion fruit Passiflora edulis Sims | FB-100-Magaury; FB-200-Yellow master; FB-300 | Mature zygotic embryo | Effect of 2,4-D and BA on somatic embryo formation. MS medium + B5 vitamins |
Induction of embryogenic calli; germination of somatic and differentiation of embryos; no conversion of embryos into plantlets | [143] |
| Passion fruit Passiflora edulis Sims | FB-300 | Mature zygotic embryos | Effect of picloram, BA, and TDZ on somatic embryo formation | Formation of somatic embryos confirmed by histochemical tests | [144] |
| Avocado Persea americana Mill. | Duke 7 | Immature zygotic embryos | Influence of semi-permeable cellulose acetate membranes on SE maturation and germination. SE induction: MS medium + picloram; SE germination: MS + BA + GA₃ |
Increase in SE germination rate: 10% (control) to 40% when SEs were prematured on cellulose acetate membranes | [145] |
| Avocado Persea americana Mill. | Duke 7 | Immature zygotic embryos | Effect of BA + GA₃ on the germination of transgenic embryogenic masses. MS + Gamborg macronutrients |
Significant improvement in the germination of transgenic somatic embryos on MS medium + BA + GA₃ | [146] |
| Avocado Persea americana Mill. | Duke 7; Reed; Haas; A10 | Immature zygotic embryos | Developing an efficient plant regeneration system from somatic embryos. SE induction: Gamborg’s B5 major salts + MS minor salts + picloram; SE maintenance: Gamborg’s B5 major salts + MS minor salts + MS vitamins + 2,4-D; SE germination: MS salts + BA + GA₃ |
Total plant regeneration (58.3%, including 43.3% bipolar regeneration) and 36.7% plant recovery rate | [147] |
| Avocado Persea americana Mill. | Duke 7 | Immature zygotic embryos | Establish a successful plant recovery system from transgenic somatic embryos. SE induction: MS medium + picloram; plant recovery: MS + TDZ + BA; micrografting: MS + BA |
Micrografts on MS + BA allowed a 60–80% success rate | [148] |
| Pomegranate Punica granatum L. | NS | Immature zygotic embryos and cotyledons (unripen fruits) | Somatic embryo formation and plant regeneration. MS + 2,4-D + BAP + KIN |
Proliferation of embryogenic cell clusters, embryo maturation, and the production of young seedlings | [149] |
| Guava Psidium guajava L. | Allahabad Safeda; Lalit; Sardar (L-49); Shweta |
Immature zygotic embryos | Effect of BAP and NAA on the germination of somatic embryos induced on 2,4-D; multiplication of plantlets on BAP | High genetic fidelity of regenerated plantlets – 99% exhibited monomorphic bands using RAPD, ISSR, and SSR markers | [82] |
| Guava Psidium guajava L. | Carabao | Nucellar tissue of immature fruits | Effect of 2,4-D, BAP, and KIN on multiplication of germinated somatic embryos | Regenerated plantlets survived ex vitro conditions but at low survival frequency | [150] |
| Grape Vitis vinifera L. | Thompson Seedless | Immature stamens | Long-term culture system for maintenance and transformation MS + 2,4-D + BAP; KIN |
Somatic embryos could be propagated over 3 years and were amenable to Agrobacterium-mediated transformation | [151] |
| Grape Vitis vinifera L. | Chardonnay | Nodal explants of in vitro plantlets | Somatic embryo production from nodal explants. ½ MS + 2,4-D + BAP |
Nodal explants produced SEs but intermodal segments, petioles, and leaf segments were not amenable to somatic embryogenesis under similar conditions | [79] |
| Grape Vitis vinifera L. | Chardonnay, Müller Thurgau, Grignolino and Brachetto a grappolo lungo |
Immature whole flowers, anthers, ovaries | Initiating somatic embryogenesis in grapevine from immature whole flower explants. Nitsch and Nitsch salts + MS vitamins + 2,4-D + BA |
No morphological differences between embryogenic cultures from anthers, ovaries, and whole flowers | [152] |
| Grape Vitis vinifera L. | Mencía | Immature stamens (anther+ filament) and ovaries from adult grown plants | Embryogenic competence of ovaries and stamens, and effect of 2,4-D; TDZ on embryogenic response Nitsch and Nitsch salts + MS vitamins + 2,4-D + TDZ |
High SE germination (87%) and plant conversion rate (88%) | [153] |
| Grape Vitis vinifera L. | Chardonnay | Immature anthers, ovaries and whole flowers | Develop a system for embryogenic culture induction, maintenance, and transformation. Embryogenic culture: MS + picloram + 2,4-D + BA Embryo germination: MS + KIN + NOA |
Establishment of a picloram-induced system for embryogenic tissue initiation, maintenance, proliferation, regeneration, and Agrobacterium-based transformation |
[154] |
2,4-D = 2,4-dichlorophenoxyacetic acid; 2iP = 2-isopentenyladenine; BA = N6-benzyladenine; BAP = benzylamino purine; CH = casein hydrochloride; GA₃ = gibberellic acid; Gln = glutamine; KIN = kinetin; IAA = indole-3-acetic acid; IBA = indole-3-butyric acid; MS = Murashige and Skoog medium; NAA = naphthalene acetic acid; NOA = 2-naphthoxyacetic acid; PGRs = plant growth regulators; SE = somatic embryo; TDZ = thidiazuron; WPM = woody plant medium; Z = Zeatin. NS = not specified.