U. Jaiswal

The encapsulation technology in fruit plants - a review.

Encapsulation technology is an exciting and rapidly growing area of biotechnological research. This has drawn tremendous attention in recent years because of its wide use in conservation and delivery of tissue cultured plants of commercial and economic importance. Production of synthetic seeds by encapsulating somatic embryos, shoot buds or any other meristmatic tissue helps in minimizing the cost of micropropagated plantlets for commercialization and final delivery. In most of fruit crops, seed propagation has not been successful because of heterozygosity of seeds, minute seed size, presence of reduced endosperm, low germination rate, and also some are having seedless varieties. Many species have desiccation-sensitive intermediate or recalcitrant seeds and can be stored for only a few weeks or months. Under these circumstances, increasing interest has been shown recently to use encapsulation technology for propagation and conservation. Many fruit plants are studied worldwide for breeding, genetic engineering, propagation, and pharmaceutical purposes. In this context, synthetic seeds would be more applicable in exchange of elite and axenic plant material between laboratories and extension centers due to small bead size and ease in handling. Due to these advantages, interest in using encapsulation technology has continuously been increasing in several fruit plant species. The purpose of this review is to focus upon current information on development of synthetic seeds in several fruit crops.

The role of abscisic acid in plant tissue culture: a review of recent progress

Abscisic acid (ABA) plays a significant role in the regulation of many physiological processes of plants. It is often used in tissue culture systems to promote somatic embryogenesis and enhance somatic embryo quality by increasing desiccation tolerance and preventing precocious germination. ABA is also employed to induce somatic embryos to enter a quiescent state in plant tissue culture systems and during synthetic seed research. Application of exogenous ABA improves in vitro conservation and the adaptive response of plant cell and tissues to various environmental stresses. ABA can act as anti-transpirant during the acclimatization of tissue culture-raised plantlets and reduces relative water loss of leaves during the ex vitro transfer of plantlets even when non-functional stomata are present. This review focuses on the possible roles of ABA in plant tissue culture and recent developments in this area.

Biotechnological advances in guava (Psidium guajava L.): recent developments and prospects for further research

AbstractsGuava (Psidium guajava L.), an important fruit crop of several tropical and sub-tropical countries, is facing several agronomic and horticultural problems such as susceptibility to many pathogens, particularly guava wilting caused by Fusarium oxysporium psidii, low fruit growth, short shelf life of fruits, high seed content, and stress sensitivity. Conventional breeding techniques have limited scope in improvement of guava owing to long juvenile period, self incompatibility, and heterozygous nature. Conventional propagation methods, i.e., cutting, grafting or stool layering, for improvement of guava already exist, but the long juvenile period has made them time consuming and cumbersome. Several biotechnological approaches such as genetic transformation may be effective practical solutions for such problems and improvement of guava. The improvement of fruit trees through genetic transformation requires an efficient regeneration system. During the past 2–3 decades, different approaches have been made for in vitro propagation of guava. An overview on the in vitro regeneration of guava via organogenesis, somatic embryogenesis, and synthetic seeds is presented. Organogenesis in several different genotypes through various explant selection from mature tree and seedling plants has been achieved. Factors affecting somatic embryogenesis in guava have been reviewed. Production of synthetic seeds using embryogenic propagules, i.e., somatic embryos and non-embryogenic vegetative propagules, i.e., shoot tips and nodal segments have also been achieved. Development of synthetic seed in guava may be applicable for propagation, short-term storage, and germplasm exchange, and distribution. An initial attempt for genetic transformation has also been reported. The purpose of this review is to focus upon the current information on in vitro propagation and biotechnological advances made in guava.

Germination and plantlet regeneration from encapsulated somatic embryos of mango (Mangifera indica L.)

Abstract Cotyledonary-stage somatic embryos (3–5 mm in length) originating from nucellar explants of Mangifera indica L. cv. Amrapali were encapsulated individually in 2% alginate gel. The encapsulated somatic embryos (ESEs) germinated successfully on 0.6% agar-gelled medium containing B5 macrosalts (half strength), Murashige and Skoog microsalts (full strength), 3% sucrose and 2.9 μM gibberellic acid. The percentage of germination of ESEs was higher than that of naked somatic embryos of the same size on the same medium. The germinability of ESEs was increased (73.61±7.08%) when the medium was supplemented with full-strength B5 macrosalts. Of the germinating ESEs, 45.83±3.40% developed into plantlets. Abscisic acid at 0.004 and 0.02 μM had no significant influence on germination and plantlet development, but caused a 3-week delay in germination. Well-developed plantlets regenerated from ESEs have been successfully established in soil.

SHOOT INITIATION AND MULTIPLICATION FROM A MATURE TREE OF TERMINALIA ARJUNA ROXB

SummaryThis study describes a protocol for the regeneration of complete plantlets of Terminalia arjuna from nodal explants of mature trees. Shoot multiplication from nodal explants was achieved by culturing on Murashige and Skoog (MS) medium containing different concentrations of 6-benzyladenine (BA), thidiazuron or kinetin, or BA in combination with α-naphthaleneacetic acid (NAA). The best shoot multiplication response was obtained from nodal explants grown on modified MS (half-strength major salts and Fe-EDTA) medium containing 4.44 μM BA and 0.53 μM NAA. Seasonal variations significantly affected the proliferation potential of nodal explants and best proliferation was observed from explants collected during April to May. Microshoots were rooted on half-strength MS medium with 4.92 μM IBA. The rooted shoots were acclimatized successfully.

Thidiazuron-induced Shoot Multiplication and Plant Regeneration in Bamboo (Dendrocalamus strictus Nees)

Thidiazuron (TDZ) stimulated shoot proliferation from different seedling explants (i.e., shoot, basal node, node and apical segment) of bamboo (Dendrocalamus strictus) when incorporated in half-strength Murashige and Skoog (MS) medium having 2% (w/v) sucrose. All the concentrations of TDZ (0.01 to 1.0 mg l−1) tried were effective in shoot proliferation. Maximum shoots (14.8 ± 1.0) were obtained from the shoot explants cultured in 0.5 mg l−1 TDZ supplemented halfstrength MS liquid medium for 21 days and subsequently transferred to the same medium devoid of TDZ. The longer culture period (i.e. 28 and 35 days) in TDZ medium caused reduction in shoot proliferation. The shoots regenerated with lower concentrations of TDZ treatment (i.e. 0.01 to 0.1 mg l−1) rooted in half-strength MS liquid medium. The shoots formed with 0.5 mg l−1 TDZ treatment did not root in basal medium and required auxin supplementation in the medium for rooting and about 55% shoots produced roots in 1.0 mg l−1 IBA supplemented medium. The shoots formed with 1.0 mg l−1 TDZ did not root even after auxin treatment. The well rooted shoots transplanted to plastic pots filled with sand and garden soil (1:1) mixture showed 98% establishment.

Alginate-encapsulation of nodal segments of guava (Psidium guajava L.) for germplasm exchange and distribution

Summary Nodal segments obtained from in vitro grown plantlets of guava (Psidium guajava L.) were encapsulated in calcium alginate beads for germplasm exchange and distribution. The best gel complex for encapsulation of nodal segments was achieved using 3% (w/v) sodium alginate and 100 mM calcium chloride.The maximum conversion of encapsulated nodal segments into plantlets was obtained on growth regulator-free, full-strength, liquid Murashige and Skoog medium after a pulse treatment with 4.4 µM BAP (6-benzylaminopurine) for 1 week prior to encapsulation. Plants regenerated from encapsulated nodal segments were acclimatised successfully. The present encapsulation approach may also be useful in large-scale propagation of desirable elite genotypes and genetically modified plants.

In Vitro Regeneration and Improvement in Tropical Fruit Trees: An Assessment

In vitro regeneration protocol has been developed for many tropical fruit trees by using juvenile as well as mature explants. Regeneration via somatic embryogenesis have been obtained in a number of cases e.g., while in citrus, sugar apple and papaya, etc. induction of androgenic haploids are successful, in guava and feijoa only callus results in anther cultures. Somaclones have helped in the selection of seedless Musa. Synthetic seed technology has aided in raising plantlets from encapsulated embryos of guava, mango, papaya, etc. Gene transfer techniques can further prove to be useful in the improvement of varieties.

Somatic Embryogenesis in Tropical Fruit Trees

Food and shelter are two basic needs of life. Since the earliest times, humans have enjoyed eating fresh fruits, as indicated by the frequent mention of fruits throughout the recorded history. The cultivation of fruits such as datepalm and pomegranate, has been dated back to 7000 to 3500 BC, respectively (Singh, 1985). In today’s world fruit play a vital role in our diet due to its nutritional importance (Nagy et al., 1990). Many fruit species are trees and with a few exceptions, e.g. banana, pineapple and strawberry, are woody. Genetic improvement of fruit crops by conventional plant breeding achieved through the selection of superior genotypes from genetically variable population derived from sexual recombination and seedling propagation (Bose, 1985). Tree architecture, floral morphology, prolonged juvenile period and irregularities in bearing habit limits the improvement of fruit trees through traditional breeding methods (Nijjar, 1977). Since most important horticultural characteristic, conferred by complexes of genes, the genetic integrity of many important fruit tree cultivars has been maintained by means of vegetative propagation. Using the conventional methods of vegetative propagation such as, cutting, layering, and grafting, substantial number of plants are produced. However, many tropical fruits and spice trees (e.g. clove) can not be propagated asexually (Litz, 1984b). Due to the increasing significance of tropical fruits for food and export income (Underhill, 1993), there has been a recent expansion of efforts and resources devoted to tropical fruit cultivar improvement. It is almost imposible to keep pace with the increasing demand of tropical fruits only through the conventional methods of plant propagation. For improvement of tropical and subtropical fruits by somatic cell genetics, a highly efficient regeneration system is a prerequisite (Litz and Jaiswal, 1991). Many programs are attempting to integrate emerging biotechnologies with conventional breeding methods to facilitate and expedite the fruit tree cultivars improvement (Litz, 1997). These include in vitro culture and micropropagation (Grosser, 1994), production of homozygous parental lines by chromosome doubling of haploids (Zhang and Lespinasse, 1992), regeneration of interspecific and intergeneric hybrids for root stock development (Gmitter et al., 1992; Ochatt et al., 1992), production of artificial seeds (Akhtar and Jaiswal, 1994; Bajaj, 1995a, b, Gray, 1987a, c; Redenbaugh, 1993), in vitro selection of somaclonal variation having enhanced diseased resistance (Hammerschlag, 1992; Jain et al., 1997), genetic transformation for specific horticultural traits (Gradner, 1993; Oliveira et al., 1996)

In vitro selection of NaCl-tolerant callus lines and regeneration of plantlets in a bamboo (Dendrocalamus strictus Nees)

SummarySodium chloride-tolerant plantlets of Dendrocalamus strictus were regenerated successfully from NaCl-tolerant embryogenic callus via somatic embryogenesis. The selection of embryogenic callus tolerant to 100 mM NaCl was made by exposing the callus to increasing (0–200 mM) concentrations of NaCl in Murashige and Skoog medium having 3% (w/v) sucrose, 0.8% (w/v) agar, 3.0 mg l−1 (13.6 μM) 2,4-dichlorophenoxyacetic acid (2,4-D), and 0.5mg l−1 (2.3μM) kinetin (callus initiation medium). The tolerance of the selected embryogenic callus to 100 mM NaCl was stable through three successive transfers on NaCl-free callus initiation medium. The tolerant embryogenic callus had high levels of Na+, sugar, free amino acids, and proline but a slight decline was recorded in K+ level. The stable 100 mM NaCl-tolerant embryogenic callus differentiated somatic embryos on maintenance medium [MS medium +3% sucrose +0.8% agar +2.0 mg l−1 (9.0 μM) 2,4-D+0.5 mg l−1 (2.3 μM) kinetin] supplemented with different (0–200 mM) concentrations of NaCl. About 39% of mature somatic embryos tolerant to 100 mM NaCl germinated and converted into plantlets in germination medium [half-strength MS+2% sucrose+0.02 mg l−1 (0.1 μM) α-naphthaleneacetic acid +0.1 mg l−1 (0.49 μM) indole-3-butyric acid] containing 100 mM NaCl. Of these plantlets about 31% established well on transplantation into a garden soil and sand (1:1) mixture containing 0.2% (w/w) NaCl.