In vitro shoot culture and microtuber induction in the steroid yam Dioscorea composita Hemsl

The individual effects of sucrose, plant growth regulators and basal salt media formulations were investigated on microtuber induction and development in shoot cultures of the steroid yam Dioscorea composita. Sucrose at 8% (w/v) was the single most significant medium constituent for microtuber induction. Of the four cytokinins tested, 6-benzyladenine at 1.25 and 2.5 μM showed strong inhibitory effects on microtuber induction. By contrast, the auxins α-naphthaleneacetic acid and indole-3-butyric acid at 5.0 μM showed striking promotive effects on microtuber induction and growth. In the presence of either one of these auxins at 5.0 μM shoot cultures produced microtubers weighing 300–400 mg fresh weight whilst kinetin, 6-(γ,γ-dimethylallylamino)-purine, 6-benzyladenine and abscisic acid failed to promote microtuber growth (microtubers weighed generally <200 mg). Media formulations Lloyd and MacCown and White supported the lowest frequencies of microtuber induction when kinetin was present at 2.5 μM. Anderson Rhododendron was as effective as Murashige and Skoog overall in promoting both microtuber induction and growth. When removed from cultures and planted in sterilized moist sand, microtubers sprouted readily (60–87% within 2 weeks) and produced vigorous shoot growth and after 5–7 months minitubers of sizes (30–80 g) suitable for direct field planting. This revised version was published online in June 2006 with corrections to the Cover Date.     

In vitro tuberization in Dioscorea alata L. ‘Brazo fuerte’ and ‘Florido’ and D. abyssinica Hoch

Nodal cuttings of D. alata L. Barzo fuerte and Florido, as well as of D. abyssinica Hoch, were cultured in vitro in order to assess the influence of the photoperiod on the production of microtubers. For both species, the highest number of microtubers was obtained under 16 and 24-h photoperiods, whereas larger microtubers were generally produced at 8-h photoperiod. In D. alata, further increase in microtuber size was observed in a culture medium where NH₄NO₃ was omitted. This effect was less noticeable in D. abyssinica.     

Effects of jasmonic acid and its methylester on in vitro microtuberisation of three food yam (Dioscorea) species

The effects of jasmonic acid (JA) applied in the medium and its methylester (MeJA) applied either in the medium or as a vapour, on shoot growth and microtuber formation were evaluated in three important food yam species (Dioscorea alata, D. cayenensis, and D. rotundata). Single nodes with leaves, derived from in vitro-multiplied material, were used as explants. When delivered at higher concentrations (10 or 50 μm) both JA and MeJA suppressed node formation. Microtuberisation was supported in all three species by adding either JA or MeJA to the medium. Significant promotory effects were observed only when photoperiod, salt compositions and sucrose concentrations known to favour microtuberisation processes in yams were used. MeJA applied as a vapour strongly inhibited microtuber differentiation in D. alata on all media tested but in D. rotundata and D. cayenensis yams MeJA, also applied in the vapour phase, exhibited slight promotory effects on microtuberisation. Received: 28 January 1998 / Revision received: 7 October 1999 / Accepted: 7 January 2000     

In vitro production of microtubers for conservation of potato germplasm: Effect of genotype,abscisic acid,and sucrose

Summary With the objective of using microtubers for conservation of potato germplasm, the main effects of genotype, abscisic acid (ABA), and sucrose level, and of their interactions on biomass production, microtuberization, microtuber dormancy, and dry matter content, were studied. ABA decreased both microtuber production and microtuber dormancy, whereas higher concentrations (60–80 gl⁻¹) of sucrose promoted biomass production, microtuber production as well as microtuber dry matter content. Microtubers stored under diffused light had longer dormancy than those kept continuously in the dark. Interactions among various factors conditioned the main effects for some characters. In vitro performance of the genotypes studied was related to their known performance under in vivo conditions for most of the characters. Microtubers produced on media devoid of ABA and containing high sucrose concentrations and N⁶-benzyladenine (44.38 μM) could be stored for 12 mo. under diffused light at 6±1°C.     

Carboxylic acids affect induction,development and quality of potato (<Emphasis Type="Italic">Solanum tuberosum</Emphasis> L.) microtubers grown <Emphasis Type="Italic">in vitro</Emphasis> from single-node explants

The role of three carboxylic acids with increasing alkyl-chain length, viz., formic, acetic and propionic acids in microtuberization was investigated in three potato (Solanum tuberosum L.) genotypes in vitro. Different concentrations of these carboxylic acids (0.0, 1.5, 3.0, 4.5 and 6.0 mM) were supplemented in microtuber induction medium, which was based on MS medium containing 8% sucrose, and their efficacy for induction, development and quality of microtubers was studied using single-node explants under continuous darkness at 20 °C. The carboxylic acids exhibited a strong stolon- and root-inhibiting effect on single-node explants with their increasing concentrations as well as alkyl-chain length (i.e., formic < acetic < propionic acids), and their mode of action was synonymous with antigibberellin substances. However, they did not have any significant inductive effect on microtuberization as compared to that under 8% sucrose medium. Rather they did show a detrimental effect on microtuber development in terms of average microtuber fresh weight with increasing concentrations as well as alkyl-chain length; both acetic and propionic acids at 6.0 mM induced the smallest microtubers in vitro. The carboxylic acids could, however, significantly increase the harvest indices suggesting their possible role in the regulation of source-sink co-ordination during microtuberization from single-node explants. But the most favourable effect of carboxylic acids on microtubers was apparent in terms of dry matter concomitant with higher starch synthesis and enhanced accumulation of reducing and total sugars. Acetic acid was the most effective in increasing the percentage of microtuber dry matter. The higher percentage of dry matter with higher carbohydrate reserves in microtubers induced by the carboxylic acids could be assumed to affect the quality of microtubers for subsequent storage, dormancy release and sprout growth.     

Effects of some growth regulators on in vitro tuberization in Dioscorea alata L. ‘Brazo fuerte’ and D. abyssinica Hoch.

Summary Nodal cuttings of Dioscorea alata L. Brazo fuerte and D. abyssinica Hoch. were cultured in vitro to assess the influence of NAA on the production of microtubers. In D. alata, high concentrations of NAA (27 and 54 M) favored the production of large microtubers, whereas the highest number of microtubers was obtained with 2.7 M. D. abyssinica was found to be more sensitive to NAA since concentrations higher than 0.27 M promoted the growth of callus on the root system. In this species, the production of the largest microtubers was obtained at 2.7 M whereas the number of microtubers was not affected by any concentration tested. In D. alata, the effects of ABA and BAP were also evaluated. The weight of the microtubers increased with increasing concentrations of ABA. This effect, however, was observed only on expiants cultured under 8 h photoperiod, but not on those cultured under 16 h. Finally the presence of BAP at concentrations as low as 0.22 M adversely affected the survival of the explants.Abbreviations ABA abscissic acid - BAP benzyl aminopurine - NAA -naphthaleneacetic acid - MS Murashige and Skoog     

Effect of washing on the plasma membrane and on stress reactions of cultured rose cells

The effects of plant growth regulators, light intensity, and end-of-day (EOD) light quality treatments on node and microtuber induction (% of cultures with microtubers) and development (fresh weight of microtubers) in yam (Dioscorea alata L. cv. Oriental) cultures were investigated. Nodal segments were excised from plantlets cultured on tuberization medium containing growth regulators and exposed to various light treatments. Absciscic acid (1 M) stimulated and cytokinins (2.5 M) inhibited microtuber development from yam nodal segments cultured on Mantell's and Hugo's full-strength tuberization medium under 8-h photoperiods. EOD far-red (FR) light inhibited microtuber induction and development and enhanced node formation. EOD FR light effects were nullified by immediately following the FR treatment with red light. This suggested the involvement of phytochrome in these processes. The lowest light intensity evaluated (12 mol m^–2 s^–1) inhibited microtuber, root and shoot production as compared to light intensities of 42, 72 and 102 mol m^–2 s^–1. Kinetin (2.5 m) in half-strength tuberization medium inhibited microtuber induction and development but did not affect node production in the light intensity evaluation.Abbreviations ABA abscisic acid - BA 6-benzylaminopurine - 2iP 6-(c,c-dimethylallylamino)-purine - NAA napthaleneacetic acid - R light red light - FR light far-red light - EOD light end-of-day light     

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.     

Axillary proliferation and tuberisation of Dioscorea cayenensis–D. rotundata complex

Yams (Dioscorea spp) are tuber crops used as staple food in Africa because of their nutritional value. However agronomic constraints, phytosanitary problems and the lack of good healthy planting material restrict their production. In contrast to the inefficiency of traditional method of planting, tissue culture techniques allow to increase the multiplication and the rapid production of pathogen- free plant material. This work was undertaken to provide farmers in African countries with healthy microplants and microtubers as seeds. In vitro nodal segments of two varieties of local yams D. cayenensis–D. rotundata complex (cv. ‘Singo’, cv. ‘Singou’ and cv. ‘Gnidou’) were micropropagated on the modified medium of Murashige and Skoog. The morphogenesis, the growth of microplants and microtuber formation have been found to be controlled by external factors that act individually and synergistically. Addition of kinetin (2 mg l⁻¹) to the culture media could reduce multiplication rate (node number) of some clones. An increase of the sucrose concentration from 3% to 5% induced no change in the multiplication and tuberisation parameters. An important reduction of the multiplication (shoot number, height and node number) and the tuberisation (tuber number and length) was observed with 8% sucrose. Multiplication (shoot and node number) was increased in the presence of jasmonic acid (10 μM). JA also induced an increase of tuber number in the absence of Kin. Multiplication of yam by in vitro growth of nodal segments is a way for rapid clonal multiplication and could allow solving the problem of lack of seed material faced by farmers. This method could also be used for multiplication of elite cultivars, independently of the growing season.     

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.     

High-frequency plant regeneration via adventitious shoot formation from deembryonated cotyledon explants of Sesamum indicum L.

Sesamum indicum L. was used as an important oil crop in the world. An efficient protocol for in vitro plant regeneration via adventitious shoot formation from deembryonated cotyledon explants isolated from mature seeds of sesame is developed. Optimal medium for direct adventitious shoot formation was Murashige and Skoog (MS) medium with 22.2 μM 6-benzylaminopurin (BA) and 5.7 μM indole-3-acetic acid (IAA). Abscisic acid (3.8 μM ABA) and AgNO₃ (29.4 μM) were effective in enhancing the frequency of adventitious shoot formation. Preculture of cotyledon explants on high sucrose concentration (6–9%) for 2 wk and subsequent transfer to 3% sucrose enhanced the frequency of adventitious shoot induction. Root formation from the adventitious shoots was easily achieved on MS medium containing 2.7 μM of α-naphthalene acetic acid (NAA). Regenerated plantlets were acclimatized on sand and peat moss (1:1), showing 95% survival with subsequent flowering and seed set. We established the high-frequency plant regeneration via adventitious shoot formation in S. indicum L.     

Regeneration through organogenesis in rattan

Organogenic cultures were induced from zygotic embryo and megagametophyte explants of the Central American cycad species, Dioon edule. Plant growth medium consisted of B5 major salts, Murashige and Skoog minor salts and organics, 400 mg l⁻¹ glutamine, 100 mg l⁻¹ arginine, 100 mg l⁻¹ asparagine, 60 g l⁻¹ sucrose, 8 g l⁻¹ Difco Bacto agar and was supplemented with kinetin (0 – 13.94 μM) and 2,4-dichlorophenoxyacetic acid (2,4-D) (0 – 9.05 μM) arranged as a 5×4 factorial in a randomized block design. Callus initiation occurred on a wide range of medium formulations from megagametophyte explants; however, shoot formation occurred only on medium supplemented with 2.26 μM 2,4-D. In comparison, callus initiation from explanted zygotic embryos occurred on fewer medium formulations, and adventitious shoot induction occurred from callus on formulations with 9.29–13.94 μM kinetin + 0.45–9.05 μM 2,4-D. Rooted shoots, derived from megagametophyte and zygotic embryo cultures, have been regenerated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Direct shoot bud induction and plant regeneration in <Emphasis Type="Italic">Capsicum frutescens</Emphasis> Mill.: influence of polyamines and polarity

Direct shoot bud induction and plant regeneration was achieved in Capsicum frutescens var. KTOC. Aseptically grown seedling explants devoid of roots, apical meristem and cotyledons were inoculated in an inverted position in medium comprising of Murashige and Skoog (Physiol Plant 15:472–497, 1962) basal medium supplemented with 2-(N-morpholine) ethanesulphonic acid buffer along with 2.28 μM indole-3-acetic acid, 10 μM silver nitrate and either of 13.31–89.77 μM benzyl adenine (BA), 9.29–23.23 μM kinetin, 0.91–9.12 μM zeatin, 2.46–9.84 μM 2-isopentenyl adenine. Profuse shoot bud induction was observed only in explants grown on a media supplemented with BA (26.63 μM) as a cytokinin source and 19.4 ± 4.2 shoot buds per explant was obtained in inverted mode under continuous light. Incorporation of polyamine inhibitors in the culture medium completely inhibited shoothoot bud induction. Incorporation of exogenous polyamines improved the induction of shoot buds under 24 h photoperiod. These buds were elongated in MS medium containing 2.8 μM gibberellic acid. Transfer of these shoots to hormone-free MS medium resulted in rooting and rooted plants were transferred to fields. This protocol can be efficiently used for mass propagation and presumably also for regeneration of genetically transformed C. frutescens.     

Factors affecting in-vitro gynogenic haploid production in niger (<Emphasis Type="Italic">Guizotia abyssinica</Emphasis> (L. f.) Cass.)

The effects of growth regulators, cold-pretreatment of flower buds, ovule (embryo sac) developmental stage and genotype on induction of gynogenesis in unpollinated ovule cultures were assessed in niger (Guizotia abyssinica (L. f.) Cass.). Indirect callus-mediated gynogenesis occurred in cvs JNC-6 and Ootacamund when the ovules were cultured on MS medium supplemented with 30 g l⁻¹ sucrose and 2,4-D either alone (0.5–2.0 μM) or in combination (2.0 μM) with different cytokinins, such as adenine, BA, 2iP and kinetin (0.5–2.0 μM). An optimum induction of gynogenesis was fostered on medium supplemented with 2.0 μM 2,4-D and 1.0 μM kinetin. Cold-pretreatment of flower buds had no stimulatory effect, but ovules collected one day before anthesis were most responsive to gynogenesis. The results showed significant variations in genotypic competence for gynogenesis with cv. Ootacamund being the most responsive (12.5%) and cv. IGP-76 the least (2.5%). Gynogenic embryos differentiated and matured on media (30 g l⁻¹ sucrose) supplemented with 0.5 μM NAA plus 1.0 μM kinetin, and 0.5 μM ABA, respectively. The haploidy (2n = 1x = 15) of gynogenic plants was confirmed by cytological analysis.     

An improved method of in vitro propagation ofDioscorea bulbifera

Nodal stem segments ofDioscorea bulbifera were induced to form plantlets in vitro. Rooted plantlets were obtained on Murashige-Skoog [14] revised medium supplemented initially with 5 mg 1⁻¹ kinetin and subsequently with 5 mg l⁻¹ indole-butyric acid. By increasing the kinetin concentration from 5 mg l⁻¹ to 10 mg l⁻¹, the number of shoots forming per node was increased from five to eight. When kinetin was substituted with 6-benzylaminopurine at only 1 mg l⁻¹, nine shoots formed on each node. Each shoot could be excised from the node and induced to form a new crop of multiple shoots. Rooted plantlets could be successfully transferred to in vivo conditions.     

Liquid culture for efficient micropropagation of Wasabia Japonica (MIQ.) matsumura

Summary An efficient protocol for in vitro propagation of the valuable medicinal plant, Wasabia japonica (Miq.) Matsumura is described through shoot tip proliferation and direct regeneration. Multiple shoots were induced from shoort tips cultured on Murashige and Skoog (MS) semi-solid medium containing various concentrations (0.5–50 μM) of N⁶-benzyladenine (BA), thidiazuron, kinetin, and zeatin. A comparison was made on shoot multiplication between semi-solid and liquid culture media. Well-developed shoots were obtained using full-strength MS semi-solid medium containing 5.0 μM BA. However, the greatest shoot proliferation was achieved on either full- or half-strength MS liquid media supplemented with 5.0 μM BA for 4 wk (15.3±0.9 and 15.0±0.7 shoots per explant, respectively), and on half-strength MS liquid medium for 6 wk (25.8±1.3 shoots per explant) in culture. In contrast, the maximum number of shoots per explant on full-strength MS semi-solid medium was achieved with either 5.0 μM BA (10.4±0.6 shoots per explant) or 10.0 μM kinetin (10.9±0.8 shoots per explant). Fresh weight of explants and length of shoots derived from full-strength MS liquid medium (1055±77 mg and 34.2±1.0 mm, respectively) were significantly higher than those derived from full-strength MS semisolid medium (437.6±17.3 mg and 15.4±0.7 mm, respectively). Quarter-strength MS liquid medium had no significant difference in shoot proliferation when compared to quarter-strength MS semi-solid medium. Elongated shoots were separated and rooted on half-strength MS semi-solid media fortified with 1-naphthaleneacetic acid (NAA), indole-3-butyric acid (IBA), or indole-3-acetic acid (IAA) ranging from 0.1 to 10.0 μM. Root formation was greatest with IBA when compared with IAA and NAA. One hundred percent of shoots were rooted on half-strength MS medium with 5.0 μM IBA, while vigorous roots were obtained with 10.0 μM IBA. Micropropagated plantlets were successfully established in soil with 95% survival rate after heardening.     

High-frequency plant regeneration from leaf-disc cultures of Jatropha curcas L.: an important biodiesel plant

A simple, high-frequency and reproducible protocol for induction of adventitious shoot buds and plant regeneration from leaf-disc cultures of Jatropha curcas L. has been developed. Adventitious shoot buds were induced from very young leaf explants of in vitro germinated seedlings as well as mature field-grown plants cultured on Murashige and Skoog’s (MS) medium supplemented with thidiazuron (TDZ) (2.27 μM), 6-benzylaminopurine (BA) (2.22 μM) and indole-3-butyric acid (IBA) (0.49 μM). The presence of TDZ in the induction medium has greater influence on the induction of adventitious shoot buds, whereas BA in the absence of TDZ promoted callus induction rather than shoot buds. Induced shoot buds were multiplied and elongated into shoots following transfer to the MS medium supplemented with BA (4.44 μM), kinetin (Kn) (2.33 μM), indole-3-acetic acid (IAA) (1.43 μM), and gibberellic acid (GA₃) (0.72 μM). Well-developed shoots were rooted on MS medium supplemented with IBA (0.5 μM) after 30 days. Regenerated plants after 2 months of acclimatization were successfully transferred to the field without visible morphological variation. This protocol might find use in mass production of true-to-type plants and in production of transgenic plants through Agrobacterium/biolistic-mediated transformation.     

<Emphasis Type="Italic">In vitro</Emphasis> propagation,microtuberization, and molecular characterization of three potato cultivars

Sprouts of potato tubers were excised from the three potato cultivars Agria, Hermes, and Spunta, sterilized and subjected to shoot formation and propagation on Murashige and Skoog (MS) medium supplemented with 1 mg dm^-3 6-benzylaminopurine (BAP) + 0.5 mg dm^-3 gibberellic acid. Shoots were rooted on MS medium supplemented with 1 mg dm^-3 indole-3-butyric acid. To increase shoot vigour prior tuber formation, shoots were subcultured on MS medium supplemented with 0.56 mg dm^-3 BAP, 0.11 mg dm^-3 2,4-dichlorophenoxyacetic acid, and 0.96 mg dm^-3 naphthaleneacetic acid. Under dark, microtuberization on MS media supplemented with 4 mg dm^-3 of both BAP and kinetin was better than 4 mg dm^-3 BAP alone, where they induced higher number of microtubers per shoot and/or the percentage of shoots that formed microtubers. The highest frequency of microtuber formation was achieved when sucrose at high concentration (8 %) was used as carbon source in culture media. Glucose ranked at the second position whereas fructose reduced the microtuber formation frequency when it was used alone or in combination with glucose. Under the applied culture conditions, cvs. Agria and Hermes showed better micropropagation and microtuberization in comparison to cv. Spunta. In addition, isozyme and RAPD techniques revealed that Agria and Hermes are closer to each other when compared with the third cultivar.     

The Effect of Plant Growth Regulators and Sucrose on the Micropropagation and Microtuberization of <Emphasis Type="Italic">Dioscorea nipponica</Emphasis> Makino

The effects of sucrose, plant growth regulators, MS (Murashige and Skoog), and ½MS salt media formulations were investigated for the development of shoot cultures, microtuber induction, and plantlet regeneration in Dioscorea nipponica. The cytokinin N-benzyladenine (BA) in the range of 0.5–2.0 mg/l showed strong enhancing effects on microtuber induction only when used in conjunction with the auxin alpha-naphthalene acetic acid (NAA), with the effect that NAA increased from 0.5 to 2.0 mg/l. Murashige and Skoog salt media supplemented with sucrose at 3% (w/v) gave the highest frequencies of shoot induction (86%) when BA was present at 2.0 mg/l and NAA at 1.0 mg/l. Sucrose at 7% (w/v) was the single most significant medium constituent for microtuber growth. The heaviest microtubers were formed on media containing 1.0 mg/l BA and 2.0 mg/l (0.073 g), especially with 7% sucrose (3.46 g). With media containing ½MS, 2% sucrose, and 0.1% (w/v) activated charcoal, the percentage of rooting was maximal when supplemented with 1.0 mg/l BA and 0.5 mg/l NAA for the in vitro produced shoots (95%) and BA and NAA both at 0.5 mg/l for the microtubers (100%). When removed from culture flasks and transferred into sterilized soil in a greenhouse, most of the hardened plantlets survived (over 91% after 1 week), and they were suitable for field planting after 1 month.     

High frequency of shoot multiplication and bulblet formation of garlic in liquid cultures

In vitro shoot proliferation and bulblet production of garlic (Allium sativum L.) was studied in liquid cultures. Shoots grown in vitro were used as explants and were cultured in MS medium supplemented with 2% (w/v) sucrose and 0.5 mg l^–1 2-iP. Three culture methods (semi-solid, liquid-immersion and raft) were compared for shoot proliferation. Explants in liquid (immersion) culture exhibited an increased multiplication rate and fresh weight of shoots after 3 weeks of culture as compared with the other treatments. Bulblet formation and growth were studied in liquid medium with different concentrations of sucrose (2–13%). MS medium containing 11% (w/v) sucrose was optimal for bulblet development and bulblets developed in this medium within 9 weeks in culture. The highest multiplication rate was (135 bulblets/explant) found when explants were cultured in bulbing medium (MS medium containing 0.1 mg l^–1 NAA+11% (w/v) sucrose) supplemented with 10 M JA. Growth retardants CCC, B-9, ABA also promoted induction and growth of bulblets. Darkness promoted the bulblet induction and growth compared to light conditions (16-h photoperiod of 50 mol m^–2 s^–1). The dormancy of bulblets was broken by cold treatment at 4 °C for 8 weeks.