The encapsulation technology in fruit plants--a review.

Development of embryogenic cell suspensions from shoot meristematic tissue in bananas and plantains (Musa spp.)

Synseed technology-a complete synthesis.

Somatic embryogenesis is a developmental process where a plant somatic cell can dedifferentiate to a totipotent embryonic stem cell that has the ability to give rise to an embryo under appropriate conditions. This new embryo can further develop into a whole plant. In woody plants, somatic embryogenesis plays a critical role in clonal propagation and is a powerful tool for synthetic seed production, germplasm conservation, and cryopreservation. A key step in somatic embryogenesis is the transition of cell fate from a somatic cell to embryo cell. Although somatic embryogenesis has already been widely used in a number of woody species, propagating adult woody plants remains difficult. In this review, we focus on molecular mechanisms of somatic embryogenesis and its practical applications in economic woody plants. Furthermore, we propose a strategy to improve the process of somatic embryogenesis using molecular means.

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Application of Somatic Embryogenesis in Woody Plants.

Nutrient-alginate encapsulation of in vitro nodal segments of pomegranate (Punica granatum L.) for germplasm distribution and exchange

We report the encapsulation of in vitro-derived nodal cuttings or shoot tips of cassava in 3% calcium alginate for storage and germplasm exchange purposes. Shoot regrowth was not significantly affected by the concentration of sucrose in the alginate matrix while root formation was. In contrast, increasing the sucrose concentration in the calcium chloride polymerisation medium significantly reduced regrowth from encapsulated nodal cuttings of accession TME 60444. Supplementing the alginate matrix with increased concentrations of 6-benzylaminopurine and α-naphthaleneacetic acid enhanced complete plant regrowth within 2 weeks. Furthermore, plant regrowth by encapsulated nodal cuttings and shoot tips was significantly affected by the duration of the storage period as shoot recovery decreased from almost 100% to 73.3% for encapsulated nodal cuttings and 94.4% to 60% for shoot tips after 28 days of storage. The high frequency of plant regrowth from alginate-coated micropropagules coupled with high viability percentage after 28 days of storage is highly encouraging for the exchange of cassava genetic resources. Such encapsulated micropropagules could be used as an alternative to synthetic seeds derived from somatic embryos.

Encapsulation of nodal cuttings and shoot tips for storage and exchange of cassava germplasm

A simplified technique which simultaneously induces and cryoprotects embryogenic calli using sucrose followed by dehydration was developed for the cryopreservation of cassava genetic resources. An initial experiment to optimise the sucrose concentration needed for both embryo production and cryoprotection showed that higher concentrations of sucrose—between 0.4 M and 0.5 M—significantly reduced the viability as well as the number of embryos produced by the embryogenic clumps in the absence of freezing. Post-thaw viability as well as embryogenic competence of clumps depended on the percentage moisture lost, duration of exposure to higher sucrose concentrations and the duration of induction of embryogenic clumps. Extending the period of cryoprotection to 21 days coupled with increased moisture loss (greater than 75%) significantly increased both post-thaw viability and the embryogenic competence of cryopreserved clumps to 95%, while reducing the duration decreased post-thaw viability. Cryopreserved callus clumps developed secondary and cyclic embryos similar to those of the non-cryopreserved controls. The optimised protocol was successfully applied to SM1-2075-1 Line 1 somatic embryos. The rate of plant recovery from cryopreserved embryos of both TME 9 and SM1-2075-1 Line 1 was comparable to that of the non-cryopreserved embryos. Successful cryopreservation of embryogenic clumps of cassava can be used to establish in vitro genebanks for long-term conservation of cassava genetic resources to complement field genebanks and other in vitro methods already being used.

Cryopreservation of embryogenic calli of cassava using sucrose cryoprotection and air desiccation

Methods for inducing high-frequency somatic embryos in cassava on cotyledons and 33 clonal accessions by the addition of supplementary copper sulphate to the induction medium were investigated. The addition of copper sulphate enhanced primary embryo induction and significantly increased secondary embryo production. All accessions from Latin America (CIAT) were embryogenically competent on medium supplemented with 8 mg l–1 2,4-dichlorophenoxyacetic acid (2,4-D) plus 1 µM copper sulphate as were 15 of the 18 accessions from Africa. The percentage of calli producing somatic embryos ranged from 7.5% in M. Bra 12 to 100% in M. Col. 1505, while the number of embryos produced per callus ranged from 0.3 in M. Bra 383 to 13.5 in TEK. The frequency of embryo production was dependent on the concentration of copper sulphate. The number of primary embryos produced per callus was also comparatively higher in the medium supplemented with copper sulphate than in the controls. The optimal concentration of copper sulphate for number of embryos produced in most accessions was 5 µM, and at this concentration the number of embryos produced was double that of the controls. Copper sulphate also reduced the maturation time of somatic embryos to 25 days from embryo initiation. High levels of 2,4-D were detrimental to embryo production. Similarly, fragmented embryos incubated in the dark produced more embryos tan those incubated under light conditions. On the basis of these results, the use of cassava somatic embryo micropropagules for germplasm conservation and synthetic seed development seems to be a strong possibility.

Induction of high-frequency somatic embryos in cassava for cryopreservation

Background: Colchicine acts as a polyploidy inducer but at high concentrations, it causes high cell mortality. To improve the efficiency of colchicine polyploidization in cassava, leaf lobes colchicine-sensitivity tests were carried out and LD50 determined at 0.00, 0.05, 0.10, 0.20 and 0.25g/l colchicine concentrations in the varieties Ankrah, Dagati, Tomfa and Tuaka. Methods: Colchicine treated leaf lobes were regenerated into callus on either 8 mg/l 2, 4-D or Picloram. The calli were subsequently regenerated into somatic embryos by NAA. LD50 of 0.09, 0.11, 0.13 and 0.09 mg/L colchicine concentration were determined for Ankrah, Dagati, Tomfa and Tuaka respectively in 2, 4-D. Similarly, LD50 of 0.12, 0.10, 0.14 and 0.10 mg/L were respectively obtained in Picloram. Result: In 2, 4-D, Ankrah and Tuaka were more sensitive to colchicine than Dagati and Tomfa whereas in picloram, Dagati and Tuaka showed more sensitivity. Callus proliferation differed significantly among varieties and influenced by the concentration of colchicine.

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Colchicine-sensitivity Test in Cassava Leaf Lobes and its Effect on Callus and Somatic Embryo Formation

An efficient callus-mediated regeneration system was developed for high-frequency production of planting material of sugarcane genotypes LSC and B36464. Spindle leaf segments cultured on MS basal medium supplemented with 2,4-D or picloram at 1, 2, 3 or 4 mg/L resulted in callus induction. Callus induction was higher on 2,4-D amended medium compared to picloram. Nevertheless, for both auxins, callus induction improved significantly (p ≤ 0.05) with increasing concentration; the highest (82 and 82.5% for B36464 and LSC respectively) was achieved at 4 mg/L. For shoot induction, calli were transferred to MS medium supplemented with BAP (0.1, 0.5, 1.0 or 1.5 mg/L). The highest number of shoots (18.13 and 16.75 for B36464 and LSC respectively) was achieved at 1.5 mg/L. Serial subculture at four-week intervals on a higher concentration of BAP (2.5 mg/L), in combination with NAA (0.5 mg/L) and GA3 (0.5 mg/L), resulted in a four-fold increase in shoot number within 16 weeks. On this medium, 40% of shoot clusters of B36464 formed well-defined shoots. On MS medium containing solely NAA (3 mg/L), 88 and 72% (B36464 and LSC respectively) formed roots. Post-flask acclimatisation of the plantlets led to 85 and 91% survival rates in LSC and B36464 respectively after which plantlets were successfully transferred to field conditions. The callus-mediated regeneration system reported in this study has the potential to sustainably provide sugarcane planting material for the emerging sugar industry in Ghana.

K. E. Danso

Papers

Encapsulation of nodal cuttings and shoot tips for storage and exchange of cassava germplasm

Cryopreservation of embryogenic calli of cassava using sucrose cryoprotection and air desiccation

Induction of high-frequency somatic embryos in cassava for cryopreservation

Colchicine-sensitivity Test in Cassava Leaf Lobes and its Effect on Callus and Somatic Embryo Formation

Efficient callus-mediated system for commercial production of sugarcane (Saccharum spp.) planting material in Ghana