Stimulation of in vitro organogenesis from epicotyl explants and successive micropropagation round in Cassia angustifolia Vahl.: an important source of sennosides

This report describes a protocol for the in vitro shoot induction and plant regeneration from epicotyl explants of Cassia angustifolia on Murashige and Skoog (MS) medium supplemented with 6-benzyladenine (BA), Kinetin and 2-iP (0.5–10.0 μM). MS medium supplemented with BA (5.0 μM) was the most effective in inducing adventitious shoots and growth. The highest rate of shoot multiplication was achieved on MS medium supplemented with BA (5.0 μM) and Indole-3-acetic acid (IAA, 1.0 μM). The nodal segments excised from the shoots regenerated from BA (5.0 μM) and IAA (1.0 μM) were used as explants for next three round of micropropagation. The number of shoots significantly increased at successive round of micropropagation. For rooting, MS medium supplemented with 2.0 μM indole-3-butyric acid proved to be better than that supplemented with IAA or α-naphthalene acetic acid. The in vitro raised plantlets with well developed shoot and roots were successfully established in earthen pots containing garden soil and were grown in greenhouse. About 52 plants (85 %) survived out of 60 plants transferred in garden soil.     

Direct plant regeneration from nodal explants of <Emphasis Type="Italic">Balanites aegyptiaca</Emphasis> L. (Del.): a valuable medicinal tree

This report describes in vitro shoot induction and plant regeneration from nodal segments of Balanites aegyptiaca on Murashige and Skoog (MS) medium fortified with 6-benzyladenine (BA), thidiazuron (TDZ) and kinetin (Kin) (0.5–20.0 μM). MS medium supplemented with BA (12.5 μM) was the most effective in inducing bud break and growth and also in initiating multiple shoot proliferation. However, the optimal level of TDZ supplementation to the culture medium was 5.0 μM. Shoot cultures were established by repeatedly subculturing the original nodal explants on the same medium. Highest number of shoots (11.5 ± 0.7) and shoot length (5.0 ± 0.2 cm) were achieved when cultures were subcultured on MS medium supplemented with 12.5 μM BA and 1.0 μM α-naphthalene acetic acid (NAA). The shoots regenerated from TDZ supplemented medium when subcultured to hormone free MS basal medium considerably increased the rate of shoot multiplication and shoot length by the end of fifth subculture. Rooting of the shoots was achieved on MS medium augmented with 1.0 μM indole-3-butyric acid (IBA) plus 0.5% activated charcoal followed by their transfer to half strength MS basal medium. The in vitro raised plantlets with well developed shoots and roots were successfully established in earthen pots containing garden soil and were grown in greenhouse with 70% survival rate. The results of this study provide the first successful report on in vitro direct plant regeneration of B. aegyptiaca.     

In vitro morphogenic response and metal accumulation in <Emphasis Type="Italic">Albizia lebbeck</Emphasis> (L.) cultures grown under metal stress

An efficient regeneration protocol for rapid mass propagation and uptake of heavy metals in Albizia lebbeck (L.), a fast growing, medicinally as well as economically important timber yielding tree was developed. Nodal segments derived from a 20-year-old tree were cultured on MS (Murashige and Skoog) medium supplemented with 10 μM 6-Benzyladenine (BA) and 1 μM α-Naphthalene acetic acid (NAA) showed optimum shoot regeneration frequency (76.6%), number of shoots (23.2 ± 0.28) per explant and shoot length (2.86 ± 0.08 cm) after 10 weeks of culture. After standardizing a reliable protocol for micropropagation, effects of ZnSO4 (0.06–0.48 mM), CuSO₄ (0.02–0.2 mM) and CdCl₂ (0.0001–0.001 mM) on shoot morphogenesis were also assessed. The regenerated shoots maintained on maintenance medium (MS + 10.0 μM BA + 1.0 μM NAA) containing ZnSO₄ (0.06 mM) showed maximum response in terms of shoot number (24.5 ± 0.83) and length (5.9 ± 0.05 cm) after 10 weeks of culture. Proline content showed an increasing trend while chlorophyll (a and b) content exhibited decreasing trend with an increased metal concentrations compared to MM cultures, and maximum increase in proline and decrease in chlorophyll content was recorded in cultures grown on Cd-enriched medium. Best rooting was accomplished on half strength MS medium with 2.0 μM IBA and ZnSO₄ (0.06 mM). The plantlets thus obtained were successfully hardened and transferred to greenhouse with 75% survival rate and exhibited normal morphological characteristics compared to donor plant.     

In vitro clonal propagation of <Emphasis Type="Italic">Balanites aegyptiaca</Emphasis> (L.) Del

In vitro propagation technique of Balanites aegyptiaca, a multipurpose woody tree was studied. Nodal segments including axillary bud from mature tree were used as an explant and their morphogenetic potential was tested on MS media with various concentrations (2.5–15.0 μM) of 6-benzyladenine (BA), Kinetin, and Thidiazuron alone or in combination with different concentrations (0.5–2.5 μM) of α-naphthalene acetic acid (NAA). Nodal segments showed axillary bud proliferation in almost all media tried. MS medium containing 12.5 μM BA alone was effective for inducing multiple shoots (5.0 ± 0.22) with an average shoot length (3.7 ± 0.26 cm) in 67% of cultures. A better shoot differentiation and elongation was achieved in a combined treatment of BA (12.5 μM) and NAA (1.0 μM). Half strength MS medium supplemented with Indole-3-butyric acid (IBA) gave the best result for rooting. The maximum frequency of root formation (68%), number of roots (5.3 ± 0.32) and root length (4.1 ± 0.38 cm) was obtained on half strength MS medium containing 1.0 μM IBA. The regenerated plantlets were potted and acclimatized successfully in a growth chamber and then moved to the greenhouse.     

An efficient in vitro process for recurrent production of cloned plants of Vitex negundo L

An efficient method for cultivation of Vitex negundo L. through axillary shoot (collected from micropropagated plants) proliferation has been successfully developed, which can be employed at a commercial scale. Axillary shoot induction was most successful using nodal explants for propagation on Murashige and Skoog (MS) medium supplemented with various concentrations of single cytokinin or in various combination with auxins. We obtained the maximum percentage (97.6 ± 1.45) response with highest number (16.4 ± 0.60) of shoots per explant on MS medium supplemented with 6-benzyladenine (BA) and ??-naphthalene acetic acid (NAA) at concentrations of 5.0 and 0.5 ??M, respectively. Shoot regeneration frequency was optimized by manipulating pH and using various media. MS medium and pH 5.8 was found to be the optimum for maximum regeneration. Nodal explants from in vitro regenerated microshoots too developed shoots, thus making the process recurrent. Shootlets with 4?C5 nodes were utilized for in vitro rooting, and best response was evaluated on MS medium supplemented with 1.0 ??M indole-3-butyric acid (IBA). The well-developed micropropagated plants were acclimatized (97%) successfully within 2 weeks in soilrite and planted ex vitro in normal garden soil, where they grew well without any morphological and genetic variations. The present regeneration process not only favoured the rapid multiplication but also expressed the regeneration capability of micropropagated plants.     

In vitro regeneration and the antioxidant enzymatic system on acclimatization of micropropagated Vitex trifolia L.

The objective of the study was to develop an in vitro shoot regeneration protocol by utilising shoot tips explant from Vitex trifolia L. Shoot tip explants obtained from a 3-year old plant was cultured on Murashige and Skoog (MS) medium supplemented with various concentrations (1.0, 2.5, 5.0, 7.5 or 10.0 µM) of thidiazuron (TDZ). The optimal level of TDZ supplementation to the culture medium was 5.0 μM for 15 d induction period. The highest number of shoots (22.2 ± 0.1) and shoot length (5.1 ± 0.1 cm) were achieved when TDZ-exposed explants were sub-cultured on MS medium containing 6-benzyladenine (1.0 µM) and 0.5 µM α-naphthalene acetic acid (NAA) after 8 weeks of culture. In vitro rooting of isolated shoots was achieved best in half-strength MS medium containing 0.5 µM NAA. During the acclimatization period, changes in activities of antioxidant enzymes were observed. Superoxide dismutase activity increased reaching maximum at 28th day after transplantation. Likewise, an upregulation of the catalase, ascorbate peroxidase and glutathione reductase enzyme activities were also observed. These observed changes reflected the ability of plants in developing an antioxidant enzymatic defence system aiding in survival against oxidative stress and in reducing release of free radicals. Plantlets were successfully hardened off and acclimatized in earthen pots containing garden soil with a survival rate of 90 %.     

Micropropagation of <Emphasis Type="Italic">Salvadora</Emphasis><Emphasis Type="Italic">persica</Emphasis>-a tree of arid horticulture and forestry

A micropropagation method for Jaal (Salvadora persica)—a tree of arid horticulture and forestry has been developed. Nodal segments of fresh shoot sprouts originated from axillary buds obtained from a plant around 35–40 years old lopped plant were used as explants for establishment of in vitro cultures. Surface-sterilized explants produced optimum number of shoots through activation of axillary buds on Murashige and Skoog’s (MS) medium containing 8.88 μM BA (6-benzyladenine) + additives (25 mgl⁻¹ each of adenine sulphate, arginine, citric acid, 50 mgl⁻¹ ascorbic acid). The shoot multiplication was influenced by the successive transfer of the mother explants for 4–5 passages. The maximum number (23.1 ± 0.73 shoots per explant) of shoots were regenerated on MS supplemented with 1.11 μM BA + 1.16 μM Kn (Kinetin) + 0.54 μM NAA (α-naphthalene acetic acid). About 90% shoots pulse-treated with a combination of 2460.27 μM Indole-3-butyric acid (IBA) + 494.56 μM NOA (2-naphthoxy acetic acid) were rooted ex vitro on soilrite within 15–18 days. Over 80% cloned plantlets were hardened successfully in a green house and transferred to polybag/pots.     

Influence of cytokinins,basal media and pH on adventitious shoot regeneration from excised root cultures of <Emphasis Type="Italic">Albizia lebbeck</Emphasis>

A highly reproducible and efficient in vitro shoot regeneration system was developed in a potential medicinal plant, Albizia lebbeck using root explants. Root explants from 15 day-old-aseptic seedlings were cultured on Murashige and Skoog (MS) medium supplemented with different concentrations (0.5, 2.5, 5.0, 7.5 and 10.0 μM) of 6-Benzyladenine (BA), Kinetin (Kn), 2-Isopentenyl adenine (2-iP) singly as well as in combination with α-Naphthalene acetic acid (NAA) (0.1, 0.5, 1.0, 1.5 and 2.0 μM). The highest rate of shoot multiplication (16.0 ± 1.87 for the average shoot number and 5.16 ± 0.38 cm for shoot length) was achieved on MS medium supplemented with 7.5 μM BA and 0.5 μM NAA. The effects of medium type, medium strength, pH and subculture on shoot induction and proliferation were also tested. An average of 21.6±2.87 shoots per explants could be obtained following this protocol. Rooting was achieved on microshoots using half strength MS medium with 2.0 μM Indole-3-butyric acid (IBA) after four weeks of culture. The in vitro raised healthy plantlets were successfully established in earthen pots containing garden soil and grown in greenhouse with >80% survival rate.     

In vitro plant regeneration from cotyledon-derived callus cultures of leguminous tree Gleditsia caspica Desf.

An in vitro regeneration system was developed using organogenic callus derived from in vitro grown cotyledonary explants of Gleditsia caspica Desf., an important leguminous tree. Murashige and Skoog (MS) basal medium augmented with 0.2 g L^?1 myo-inositol and various concentrations of either 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid, or indole-3-butyric acid (IBA) alone as well as combined with cytokinins was used for callus induction. The highest frequency of organogenic yellowish-white and nodular callus (93 %) was obtained from explants grown on medium supplemented with 13.5 μM 2,4-D and 4.4 μM benzyladenine (BA). The yellowish-white and nodular callus when transferred to MS medium supplemented with BA (2.2–17.7 μM) or kinetin (KT; 2.3–18.8 μM) solely or in combination with 2.3 μM 2,4-D produced several microshoots after 5 weeks culture. The calli cultured on MS medium with 4.4 μM BA singly showed superior growth response and produced both maximum shoot regeneration (94 %) and the highest mean number (4.3) of microshoots per callus. Transfer of regenerated microshoots onto modified MS basal medium fortified with 5.8 μM gibberellic acid and 4.4 μM BA resulted in the maximum number of internodes per shoot and the highest shoot elongation after a period of 6 weeks. Optimum rooting of 90 %, an average 6.1 roots per shoot, and a mean root length of 3.6 cm was observed when half-strength MS medium was supplemented with 9.8 μM IBA and 0.92 μM KT. The regenerated healthy plants with well-developed shoots and roots showed a survival rate of 77 % after acclimatization and transplanting to garden soil for a 10-week hardening period under ex vitro conditions.     

Plantlet regeneration of adult <Emphasis Type="Italic">Pinus massoniana</Emphasis> Lamb. trees using explants collected in March and thidiazuron in culture medium

A protocol for micropropagation using nodal explants from mature Pinus massoniana trees has been developed. Time of explant collection is crucial for the initial success of aseptic culture. Explants collected in early March gave the highest percentage of explant survival (64.5%) and shoot-forming percentage (52.3%). Thidiazuron (TDZ) concentration significantly influenced shoot formation; 4 μM TDZ was optimum, with 4.8 shoots produced per explant with a mean length of 7.1 cm after 120 days of culture. Regenerated shoots rooted for 60 days in basic medium with 1 μM NAA were ready for growth in pots. This is the first report on plantlet regeneration in vitro from mature trees of P. massoniana that provides a reliable method for propagating selected elites.     

Non-aerated liquid culture promotes shoot organogenesis in <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Labill

Eucalyptus is very recalcitrant to in vitro culture. In this research, an efficient shoot organogenesis system was developed using 60-day-old plants of Eucalyptus globulus grown in vitro and non-aerated liquid medium to improve shoot proliferation. Cultures were initiated with hypocotyls and leaf segments from plantlets cultivated on semisolid ½ MS modified medium supplemented with 4.44 µM 6-Benzyladenine (BA) and 16.1 µM 1-Naphthaleneacetic acid (NAA). Calli were transferred to shoot induction medium, with either 0.5 or 2.7 µM NAA. Shoot multiplication was carried out on 4.44 µM BA + 0.5 µM NAA medium, and semisolid and non-aerated liquid systems were compared for improving shoot proliferation. Rooting of adventitious shoots was evaluated on medium containing NAA or Indole-3-butyric acid -IBA (5 and 16 µM). Callogenesis was obtained from both types of explants, although shoot formation was only obtained from leaf-derived calli. Shoot proliferation on 4.44 µM BA + 0.5 µM NAA resulted in the most shoots/callus. Non-aerated liquid medium was more efficient in promoting shoot multiplication (53.5 shoots/callus) than was semisolid medium (28.5 shoots/callus). Levels of phenolic compounds were significantly reduced in the shoots cultivated in liquid medium. Efficient rooting (76%) was obtained using 16 µM IBA.     

Direct shoot bud regeneration from shoot tip explants of <Emphasis Type="Italic">Enicostema axillare</Emphasis>: an important medicinal plant

An efficient protocol has been developed for in vitro propagation of Enicostema axillare using shoot tip explants. The shoot tip explants were cultured on MS medium supplemented with various combinations of (BAP, KIN) and (NAA/IAA & IBA) in different concentrations between 0.5 and 2.0 mg/l for multiple shoot bud induction. The highest percent of (98.51 %) was observed at 1.0 mg/l BAP in combination with 0.2 mg/l KIN while maximum number of shoot buds (8.41 shoots/explant) was noticed on MS medium containing 1.0 mg/l BAP and 0.2 mg/l KIN combination. The highest frequency (90.82 %) of multiple shoot bud regeneration was observed at 1.0 mg/l BAP and 0.5 mg/l IBA with 15.12 ± 2.12 shoots/explants. The regenerated multiple shoots were transferred to half-strength MS medium augmented with different concentration of 0.5–2.5 mg/l IBA for rooting. Among the different concentrations of IBA tested, maximum percentage of rooting (100 %) was observed in MS medium augmented with 1.5 mg/l IBA. The rooted plantlets were successfully transferred into plastic cups containing soil and sand in the ratio of 1:1. Subsequently established in the field conditions with 90 % of survival rate. The protocol developed can be utilized for both large scale plant production and conservation of germplasm of this species. The described method can be successfully employed for large-scale multiplication and in vitro conservation as well as production of secondary metabolites of E. axillare.     

Direct shoot organogenesis from leaf explants of Embelia ribes Burm. f.: a vulnerable medicinal plant

An efficient system was developed for direct plant regeneration from in vitro-derived leaf explants of Embelia ribes Burm. f., a vulnerable medicinal woody climber of the Western Ghats of India. The in vitro procedure involved three steps that included induction of shoot initials from leaf tissue, regeneration and elongation of shoots from the shoot initials, and rooting of shoots. The induction of shoot initials was achieved on Murashige and Skoog (MS) solid medium supplemented with different concentrations of thidiazuron (TDZ). The best medium for shoot induction was MS with 0.272 μM TDZ. Numerous shoot primordia developed within 2–3 weeks on the leaf margin as well as on the midrib region, without any callus phase. In the second step, the shoot clumps separated from the leaf explant on transfer to MS basal medium, resulting in the differentiation of 90% of the shoot initials into well-developed shoots. The 2- to 3-cm-long shoots rooted on half-strength MS basal medium supplemented with 4.90 μM indole-3-butyric acid (IBA) and 3% (w/v) sucrose in the third stage. The rooted plants could be established in soil with 70% success. This protocol could be utilized for in vitro propagation and conservation of this important threatened medicinal plant.     

Micropropagation of red sanders (Pterocarpus santalinus L.) using mature nodal explants

In vitro clonal multiplication of Pterocarpus santalinus L. was achieved using mature nodal explants of a 10-year-old elite quality tree. Combinations of serial transfer technique and incorporation of antioxidants (250 mg/l L-ascorbic acid and 50 mg/l citric acid) into the culture medium helped to minimize medium browning and improve explant survival during shoot sprouting. About 70% of explants were sprouted on Murashige and Skoog (MS) liquid medium containing 4.4 μM 6-benzyladenine (BA). The explant harvest period also influenced the bud break and shoot sprouting in nodal explants. The combination of 4.4 μM BA and 2.2 μM thidiazuron (TDZ) was found to be the most suitable growth regulator for obtaining the highest percentage of nodal segment sprouting (74%–75%), the number of secondary shoots per primary shoot (two or three), the shoot length (5–6 cm), the number of new nodal segments generated per active explant (four or five), and the multiplication coefficient (3.5) within 6 weeks. Repeated subculturing of nodal explants obtained from shoot cultures enabled continuous production of healthy axillary shoots. At the end of the sixth passage, about 90% of nodal explants produced five or six healthy green shoots, each being about 6.6 cm long with six or seven nodes. Multiplication coefficient was also increased from the first subculture (5.4) to the sixth subculture (8.3). The best rooting response was achieved on solidified half-strength MS medium supplemented with 4.9 μM indole-3-butyric acid (IBA). About 70% of the micropropagated plantlets were established successfully in 20-cm pots containing a mixture of soil and farmyard manure (4 : 1 ratio) and formed new leaflets.     

Rapid clonal multiplication of a woody tree, <Emphasis Type="Italic">Vitex negundo</Emphasis> L. through axillary shoots proliferation

An efficient and improved shoot regeneration technique for the micropropagation of Vitex negundo, an aromatic and medicinal shrub through in vitro culture of nodal segments with axillary buds, is described. Thidiazuron (TDZ) used at 1.0 μM was the most effective in inducing bud break and growth, and also in initiating multiple shoot proliferation at the rate of 25 microshoots per nodal explant with axillary buds, after 4 weeks of culture. By repeated subculturing of nodal explants, a high-frequency multiplication rate was established. Optimum shoot multiplication and elongation was achieved when TDZ exposed explants were subcultured on Murashige and Skoog (MS) media containing a combination of 1.0 μM 6-benzyladenine (BA) and 0.5 μM α-naphthalene acetic acid (NAA). Efficient rooting was achieved directly in soilrite when basal portion of the shoots were treated with 500 μM indole-3-butyric acid for 10 min which was the most effective in inducing roots, as 97% of the microshoots produced roots. Plantlets went through a hardening phase in a controlled plant growth chamber, prior to ex-vitro transfer. Micropropagated plants grew well, attained maturity and flowered. No phenotypical differences for morphogenesis were observed among the regenerants.     

Micropropagation of mature Terminalia catappa (Indian Almond), a medicinally important forest tree

We report an efficient in vitro propagation method for Terminalia catappa using nodal segments of a 15-year-old mature tree. The nodal segments were cultured on MS medium supplemented with 6-benzyladenine (BA; 0.5–3.0 mg l⁻¹) or Kinetin (Kn; 0.5–3.0 mg l⁻¹) for bud breaking and multiple shoot induction. About 85% of the explant responded (2.8 ± 0.41 shoots per node with 2.7 ± 0.14 cm length) within 15 days of inoculation in Murashige and Skoog medium fortified with 2.0 mg l⁻¹ of BA. Further shoot multiplication was achieved by repeated transfer of mother explants and subculturing of in vitro-produced shoots on medium supplemented with various concentrations of BA (0.25–1.5 mg l⁻¹) or Kn (0.25–1.5 mg l⁻¹) or on their combinations. Optimal number of shoots and shoot length were recorded on MS medium supplemented with 0.25 mg l⁻¹ of BA and 0.25 mg l⁻¹ of Kn. The multiplied shoots were used for ex vitro rooting after treatment for 4 min with indole-3-butyric acid (IBA; 50–500 mg l⁻¹) or α-naphthalene acetic acid (NAA; 50–500 mg l⁻¹). About 80% of the shoots treated with 200 mg l⁻¹ of IBA produced ex vitro roots with an average of 2.8 roots per shoot. Nearly 75% of these plantlets could be acclimatized within 5 weeks and successfully established in the field. This is the first report on micropropagation of T. catappa, which can be applied for further genetic transformation assays and pharmaceutical purposes.     

Efficient in vitro regeneration of <Emphasis Type="Italic">Leucaena leucocephala</Emphasis> using immature zygotic embryos as explants

A method for efficient in vitro regeneration of Leucaena leucocephala cv. K636 was developed using immature zygotic embryos as the explant. Multiple shoot induction was achieved by culturing the explants on half-strength Murashige and Skoog (MS) medium supplemented with thidiazuron (TDZ) (0.03 to 1.5 μM). The maximum number of shoots per explants was achieved in 0.26 μM TDZ-supplemented media. TDZ concentration significantly influenced the induction of multiple shoots as well as the shoot-length. TDZ at 0.35 μM or higher concentrations resulted in abnormal stunted shoots. Full-strength MS media devoid of any plant growth regulator were used for shoot elongation. In vitro root induction was achieved in half-strength MS media supplemented either with 0.54 μM 1-naphthaleneacetic acid (NAA) or with 14.76 μM indole-3-butyric acid (IBA) in combination with 0.23 μM kinetin (Kn). Media supplemented with 14.76 μM IBA in combination with 0.23 μM Kn induced twofold–threefold more roots than media supplemented with 0.54 μM NAA. However, the average root length was lower in 14.76 μM IBA in combination with 0.23 μM Kn than in 0.54 μM NAA. Regenerated plants were maintained under normal condition after hardening. Plants, which were rooted on media supplemented with 14.76 μM IBA in combination with 0.23 μM Kn showed higher survival rate during hardening than those rooted on 0.54 μM NAA supplemented media.     

In vitro clonal propagation of mature Tectona grandis through axillary bud proliferation

An in vitro clonal propagation procedure for mature Tectona grandis (teak) trees is described. Multiple shoots were induced from nodal segments through axillary bud proliferation. A shoot multiplication rate of 6.33 was achieved on Murashige and Skoog's (MS) medium supplemented with 10 μM 6-benzyladenine BA and 1 μM 1-naphthalene acetic acid (NAA) during every subculture cycle of 4 weeks. In vitro raised shoots could be successfully rooted (66.66%) on liquid MS medium supplemented with 15 μM NAA, with 1.60 roots per shoot, every 6 weeks of culture. In vitro hardening was carried out in sand soaked with half-strength MS medium (organic free). The plantlets were acclimatized first in a mist chamber and then in polybags in a mixture of soil, sand, and farmyard manure (1 : 1 : 1 v/v) in a shade house.     

Factors influencing direct shoot regeneration from leaves,petioles, and plantlet roots of triploid hybrid <Emphasis Type="Italic">Populus</Emphasis> sect. <Emphasis Type="Italic">Tacamahaca</Emphasis>

Since the generation of full-sib artificial triploid families, rapid clone establishment and genetic improvements have been needed. Here, we report an in vitro method of direct shoot regeneration of a triploid hybrid poplar [(Populus simonii × P. nigra ‘Italica’) × (P. × ‘popularis’)]. Using different randomized block designs, we selected one triploid to evaluate the explant type, optimal concentrations of plant growth regulators and agar, and culture time under light or dark conditions over 60 days. The highest rate of shoot induction, 80.0%, was obtained using Murashige and Skoog (MS) medium supplemented with 0.2 mg/L benzyladenine, 0.04 mg/L naphthaleneacetic acid (NAA), and 5.5 g/L agar for the first 30 days in the dark, then 3 g/L agar for the next 30 days in light. This last medium yielded the best rate of shoot induction (6.32 shoots/explant). These three media were also used to evaluate the influence of the genotypes of the parents and hybrid triploids on regeneration. Two parents and three of the four full-sib triploids were regenerated successfully; different genotypes and explant types significantly affected the rate of shoot induction and average number of shoots. Leaves but not petioles were a suitable explant. One genotype produced the highest rate of shoot induction of 96.67%. Half-strength MS medium supplemented with 0.2 mg/L indole butyric acid and 0.04 mg/L NAA was the most effective for rooting; rooting rate was 96.67%, survival rate of transplants was 73.33%, and rooting frequency surpassed 85% for each genotype. Overall, this in vitro regeneration system will be useful for the propagation and genetic modification of triploid poplars.     

Micropropagation of <Emphasis Type="Italic">Eucalyptus grandis</Emphasis> × <Emphasis Type="Italic">E. urophylla</Emphasis> AEC 224 clone

Genetic transformation systems require protocols that allow regenerating transgenic plants from transformed tissues. This study aimed to establish a protocol for indirect organogenesis in leaf explants of a Eucalyptus grandis  ×  E. urophylla AEC 224 clone. During callogenesis stage, several concentrations of NAA and then NAA or 2,4-D combined with TDZ were tested in JADS culture medium for 30 days, followed by subculture of the explants in the regeneration medium, containing 5.0 µM BA and 0.5 µM NAA for another 30 days. In these media, the explant oxidation rate was high (95 %). Thus, in order to reduce oxidation, different culture media were compared: WPM, MS, JADS and modified QL, followed by explant transfer onto regeneration medium. The highest percentage of regeneration and the lowest oxidation rate were achieved on WPM medium. Then, NAA and 2,4-D were tested in combination with TDZ and also TDZ and BA combined with NAA in WPM medium. The most efficient culture media in terms of shoot regeneration were WPM supplemented with 0.25 µM TDZ and 0.1 µM NAA during 30 days for callus induction and then with 5.0 µM BA and 0.5 µM NAA for another 30 days. This protocol yielded a regeneration rate of 43 %, with a low oxidation of tissues. A rooting experiment was conducted using half strength MS medium and comparing three concentrations of IBA (2.46, 4.90 and 7.35 µM). The highest rooting percentage (35 %) was obtained on medium containing 2.46 µM IBA. Once the shoots were rooted, acclimatization in a greenhouse was not challenging and plant survival reached 100 %.