Germplasm Preservation of Wild Arachis Species through Culture of Shoot Apices and Axillary Buds from In Vitro Plants

A study was conducted to evaluate in vitro techniques for germplasm preservation of wild species of Arachis. Nodal segments excised from in vitro-grown plants of A. retusa, A. macedoi and A. burchellii were used to examine the effects of explant position and age of the donor plant. Explants were excised from plants maintained in culture for 30, 60, 90 or 180 d, numbered I – V from top to bottom and cultured on MS medium supplemented with 2.7 µM NAA or different BAP concentrations (0, 4.4, 13.2 and 22 µM). The age of the donor plant has not influenced the responses of the four genotypes studied. In contrast, shoot regeneration ability was significantly affected by the original explant position, decreasing from top to bottom. In media supplemented with different BAP concentrations, multishoot formation was induced from apical segments at low frequencies (10 – 20%) and segments of all positions originated calluses at the explant basis after 30 d of culture. The culture of nodal segments in the presence of 2.7 µM NAA as the sole growth regulator is recommended for the multiplication of in vitro collections of wild groundnut species in order to avoid callusing and adventitious shoot formation.     

Ricerche Sull'Abscissione Nell'Olivo. I. Studio Morfogenetico Dell'Abscissione Fogliare

Abstract

Galls and regeneration in P. capillacea. – Galls arose from some cultured segments of Pterocladia capillacea in winter trough regeneration from cut-surfaces, especially at the proximal end. Bacteria were always present on the thallus and inside the old galls. They might be the agents of cecidogenesis, even though we never obtained galls in segments treated with these agents. We suggest that gall formation can be induced by bacteria only in winter, when the stimulus of natural differentiation appears to be very low.     

Nutrient alginate encapsulation of nodal segments of Althaea officinalis L., for short-term conservation and germplasm exchange

Abstract

In the present study, an alternate method for germplasm storage in the form of artificial seeds was standardized via nodal explants excised from in vitro proliferated shoots. The explants were encapsulated using sodium alginate and calcium chloride as gelling matrix. For development of root along with shoot, excised nodal segments were pretreated with ½ MS medium along with 20 μM IBA for 24 h and encapsulation was carried thereafter. Combination of 3% sodium alginate augmented with 100 mM CaCl₂.2H₂O was found appropriate for the formation of clear and uniform beads and subsequent conversion of encapsulated nodal segments into plantlets. Maximum (66%) encapsulated nodal segments were converted into plantlets on MS medium supplemented with 7.5 μM BA and 0.5 μM NAA after eight weeks. Regeneration frequency of auxin-pretreated encapsulated and non-encapsulated nodal segments (stored at 4 ºC) was evaluated at different storage time (0 to 6 weeks). After four weeks of storage, encapsulated propagules exhibited highest conversion response on the optimized medium after eight weeks of culture. Plantlets were hardened and established with success in ex vitro conditions. Conversion of synthetic seeds into plantlets was observed when these were directly sown in autoclaved Soilrite^TM (Keltech Energies, Bangalore, India).     

Micropropagation of juvenile and adult Sorbus domestica L.

Successful propagation of seedlings and mature trees of Sorbus domestica L. has been achieved by in vitro methods. Multiple shoot formation was obtained by placing shoot apices or nodal segments on a modified Schenck and Hildebrandt medium containing benzyladenine. Regenerated shoots were excised and induced to root on media with auxin. In the best treatments 75–85% of shoots from juvenile material rooted. Rooting capacity of shoots from mature explants was lower (30%) and was not improved by dipping the base of shoots in concentration solutions of indolebutyric or naphthaleneacetic acids. Plantlets were ultimately established in soil.Abbreviations BA benzyladenine - IAA indoleacetic acid - IBA indolebutyric acid - NAA naphthaleneacetic acid     

A role for ALF4 during gall and giant cell development in the biotic interaction between Arabidopsis and Meloidogyne spp.

Root‐knot nematodes (RKNs; Meloidogyne spp.) are a major pest for the agriculture worldwide. RKNs induce specialized feeding cells (giant cells, GCs) inside galls which are de novo formed pseudo‐organs in the roots that share similarities with other developmental processes as lateral root (LR) and callus formation or grafting involving new vascular development or pericycle proliferation. Hence, it is pertinent to study the molecular mechanisms directing the plant‐nematode interaction. In this respect, ALF4 is a key gene during LR formation, vascular vessels reconnection in grafting, hormone‐induced callus formation or de novo root organogenesis from leaf explants. Our results show that ALF4 is also induced in galls at early infection stages in an auxin‐independent way. Furthermore, ALF4 activity is necessary for the formation of proper galls and GCs, as the mutant alf4‐1 presents aberrant galls and GCs with severe structural abnormalities leading to a dramatic reduction in the nematode egg production. However, a low‐reproduction rate is maintained, that might be explained by the local auxin maximum build by the nematodes in galls, partially rescuing alf4‐1 phenotype. This would be similar to the partial rescue described for LR formation with exogenous auxins and also agrees with the LR emergence from alf4‐1 galls but not from uninfected roots. In addition, ALF4 is also induced in syncytia formed by cyst nematodes. All these data support a pivotal role for ALF4 during de novo organogenesis processes induced by endoparasitic nematodes, in addition to its role in LR formation, callus development or vessel reconnection during grafting.     

Influence of light spectra and elicitors on growth and ascaridole content using in vitro cultures of Dysphania ambrosioides L.

Dysphania ambrosioides L. is a medicinal plant with anti-helmintic potential. The aim of this study was to evaluate separately the effect of light spectra and elicitors on Dysphania ambrosioides growth and volatile constituents in vitro. Thus, plantlets were first cultured under blue (B), red (R), white, combinations of B:R (1:1, 2:1, 1:2) from LEDs and fluorescent lamps. Secondly, nodal segments were inoculated in the medium supplemented with chitosan (0, 50, 100, 150, and 200 mg L^??1) and salicylic acid (0, 3, 6, 9, and 12 mg L^??1). After 40 days of cultivation, the growth parameters and chemical composition of volatile constituents were evaluated. The light spectra significantly influenced in vitro growth of D. ambrosioides. The best growth occured using white LED or a blue:red combination of 2:1. It was also observed that the blue LEDs inhibited the synthesis of Z-ascaridole, while fluorescent light promoted a greater conversion of α-terpinene into ascaridole. The elicitors, chitosan and salicylic acid had a negative effect on the growth of nodal segments. However, the highest Z-ascaridole content was obtained at 50 to 100 mg L^??1 of chitosan and with 6 to 9 mg L^??1 of salicylic acid. The present study demonstrates that shoots regenerated from nodal segments exposed to different light spectra or on MS medium containing chitosan and salicylic acid can exhibit an altered growth and increased volatile constituents of interest.

     

Symbiotic Fungal Flora in Leaf Galls Induced by <Emphasis Type="BoldItalic">Illiciomyia yukawai</Emphasis> (Diptera: Cecidomyiidae) and in Its Mycangia

We investigated the association between a gall midge, Illiciomyia yukawai, and its symbiotic fungi on Japanese star anise, Illicium anisatum. The number of fungal species isolated from the galls increased with development of the galls, whereas those from the leaves showed a different trend. Botryosphaeria dothidea was dominant in the galls from June to October, and after that Phomopsis sp. 1, Colletotrichum sp., and Pestalotiopsis sp. became dominant. Although B. dothidea was not isolated from the leaves, it was detected from mycangia (abdominal sternite VII) of egg-laying adults at a high isolation frequency (>90%). However, B. dothidea was not isolated from mycangia of adults emerging from galls that were enclosed by plastic bags. This indicates that I. yukawai is closely associated with B. dothidea and that its newly emerged adults do not take the fungus into mycangia directly from the galls where they had developed. Also, the fungus from the fungal layers of ambrosia galls has less ability to propagate on artificial media despite the presence of its mycelial mass in mature galls.     

Indole Glucosinolates and Camalexin do not Influence the Development of the Clubroot Disease in Arabidopsis thaliana

Root galls of Brassicaceae caused by Plasmodiophora brassicae are dependent on increased auxin and cytokinin formation. In this study we investigated whether indole glucosinolates are involved in indole‐3‐acetic acid (IAA) biosynthesis in root galls, by using a genetic approach. The cytochrome P450 enzymes, CYP79B2 and CYP79B3, convert tryptophan to indole‐3‐acetaldoxime (IAOx), which is a precursor for indole glucosinolates and the phytoalexin camalexin in Arabidopsis thaliana. Root galls of the Arabidopsis ecotypes Wassilewskija (WS) and Columbia (Col) accumulated camalexin, WS at levels up to 320 μg/g dry weight. By contrast, camalexin was absent in root galls of cyp79b2/b3 double mutants. Infection rate and disease index as a measure of club development in mutant and wild‐type plants of the two ecotypes were investigated and no differences were found in gall formation. This demonstrates that camalexin is an ineffective inhibitor of P. brassicae and indole glucosinolates are not the source of elevated levels of IAA in galls, because free IAA levels in mutant galls were comparable with those in wild type.     

Influence of type of explant,plant growth regulators,salt composition of basal medium,and light on callogenesis and regeneration in <Emphasis Type="Italic">Passiflora suberosa</Emphasis> L. (Passifloraceae)

Passiflora suberosa is used in popular medicine, improvement programs, and as an ornamental plant. The goal of this study was to establish efficient protocols for plant regeneration and callus induction from nodal, internodal and leaf segments excised from in vitro-grown plants. The different morphogenetic responses were modulated by the type and concentration of plant growth regulators, according to the basal medium and light conditions. Shoot formation occurred through three pathways: (1) development of preexisting meristems, (2) direct organogenesis, and (3) indirect organogenesis. Development of preexisting meristems was observed from nodal segments (1 shoot/explant) in response to α-naphthaleneacetic acid (NAA), picloram (PIC), and 2,4-dichlorophenoxyacetic acid (2,4-D), using two basal media (MS and MSM). Direct organogenesis in this species was obtained for the first time in this work, through shoot development from internodal segments in the presence of 6-benzyladenine (BA). The highest regeneration rates were achieved on MSM medium, regardless of the BA concentration. Indirect organogenesis was achieved from all explant types on media supplemented with BA, used alone or in combination with NAA. The highest regeneration efficiency was obtained from internodal segments cultured on MSM medium plus 44.4 μM BA. Compact, friable, or mucilaginous non-morphogenic calluses were induced by thidiazuron, PIC, 2,4-D, and NAA. High-yielding friable calluses obtained on MSM medium supplemented with 28.9 μM PIC are being used for the establishment of suspension cultures and further analysis of the production of bioactive compounds.     

Nine new species of Dasineura (Diptera: Cecidomyiidae) from flowers of Australian Acacia (Mimosaceae)

Abstract. Thirteen species of Australian acacias are invasive plants in agricultural and native vegetation areas of South Africa. Biological control programmes for Australian acacias in South Africa have been implemented and are aimed at suppressing reproductive vigour and, in some cases, vegetative growth of these weeds. Gall-forming midges are under consideration as potential biological control agents for invasive acacias in South Africa. Entomological surveys in southern Australia found a diverse cecidomyiid fauna associated with the buds, flowers and fruits of Acacia species. Nine new Dasineura species are described and two species, D. acaciaelongifoliae (Skuse) and D. dielsi Rübsaamen, are redescribed. The newly described taxa are D. fistulosa sp.n. , D. furcata sp.n. , D. glauca sp.n. , D. glomerata sp.n. , D. oldfieldii sp.n. , D. oshanesii sp.n. , D. pilifera sp.n. , D. rubiformis sp.n. and D. sulcata sp.n. All eleven species induce galls on ovaries and prevent the formation of fruit. Two general types of gall are caused. Type A comprises woody, tubular galls with larvae living inside ovaries (D. acaciaelongifoliae, D. dielsi, D. fistulosa, D. furcata, D. glauca, D. glomerata, D. oldfieldii). Type B includes soft-tissued, globose galls that belong to four subtypes: inflated, baglike, hairy galls with larvae living between ovaries (D. pilifera); pyriform, pubescent swellings with larvae living inside ovaries (D. rubiformis); globose, hairy, swellings with larvae living superficially on ovaries in ovoid chambers (D. oshanesii); and inconspicuous, glabrous swellings with larvae living superficially on ovaries in shallow groovelike chambers (D. sulcata). The gall types are associated with a particular pupation pattern. In type A galls, larvae pupate within larval chambers in galls, whereas in type B galls pupation takes place between ovaries in galls or in the soil beneath the host tree. Gall midges responsible for the same general gall type are morphologically related and differ from species causing the other gall type. Phylogenetic analysis of a 410 bp fragment of the mitochondrial cytochrome b gene supports the division of the gall midge species into two groups except for D. sulcata, which appears as a subgroup of the group causing type A galls. The interspecific divergence values in group A species were between 0.5 and 3.9% with intraspecific divergence estimates of 0–0.2%. Gall midges causing type B galls had interspecific divergence values of 4.6–7.3% and intraspecific divergence values of 0–3.7%. Closely related biology and morphology together with low cytochrome b divergence estimates suggest a more recent speciation in group A when compared with species of group B. Dasineura rubiformis and D. dielsi are proposed as potential biological control agents for Acacia mearnsii De Wild. and Acacia cyclops A. Cunn. ex G. Don, respectively, in South Africa due to their narrow host range and ability to form high population densities that reduce seed formation. Both species produce galls with low biomass, which makes them compatible with commercial exploitation of their host species in Africa.     

In vitro germplasm conservation of high Δ<Superscript>9</Superscript>-tetrahydrocannabinol yielding elite clones of <Emphasis Type="Italic">Cannabis sativa</Emphasis> L. under slow growth conditions

Germplasm conservation of a high Δ⁹-tetrahydrocannabinol yielding variety of Cannabis sativa L. was attempted using synthetic seed technology and media supplemented with osmotic agents. Explants of nodal segments containing single axillary bud were excised from in vitro proliferated shoot cultures and encapsulated in high-density sodium alginate (230 mM) hardened by 50 mM CaCl₂. The ‘encapsulated’ (synthetic seeds) and ‘non-encapsulated’ nodal segments were stored at 5, 15 and 25°C for 8, 16 and 24 weeks and monitored for the re-growth and survival frequency under the tissue culture conditions (16-h photoperiod, 25°C) on Murashige and Skoog (MS) medium supplemented with thidiazuron (TDZ 0.5 μM). ‘Encapsulated’ nodal segments could be stored at low temperature 15°C up to 24 weeks with maximum re-growth ability and survival frequency of 60%. Similar to ‘encapsulated’ cultures, the highest re-growth in ‘non-encapsulated’ cultures was observed in the explants kept at 15°C without osmotic agents. Furthermore, the effect of osmotic agents mannitol and sorbitol (2 and 4% w/v, added individually and in combination to the media at culture room conditions i.e. 25°C) on non-encapsulated shoot cultures was also evaluated. A considerable decrease in re-growth and survival was observed in the cultures treated with osmotic agents. Among the cultures treated with different concentrations of osmotic agents, the highest rate of re-growth and survival was observed at the lowest concentration of 2% sorbitol and 2% mannitol individually added to the media. Well-developed plantlets regenerated from ‘encapsulated’ nodal segments were successfully acclimatized inside the growing room with 90% survival frequency. Gas chromatography-flame ionization detection (GC-FID) was used to compare the chemical profile and the concentration of the different cannabinoids (cannabidiol, cannabichromene, cannabigerol, cannabinol, Δ⁹-tetrahydrocannabinol and tetrahydrocannabivarin) of the plants grown from ‘encapsulated’ nodal segments to that of the donor plant. The data showed similar cannabinoid profile and insignificant differences in the cannabinoids content between the two types of plants. This study is of high significance since the encapsulation technology would allow the prolonged storage (thus reducing the cost of labor) of high-yielding C. sativa germplasm selected for the isolation of THC, a high-value bulk active pharmaceutic.     

Competition and niche relationships among Eriosoma aphids occurring on the Japanese elm

Summary Galls of more than one species of Eriosoma (Aphidoidea) are found sympatrically even on single trees. Incipient galls are frequently invaded by conspecific and/or allospecific fundatrices. Eriosoma yangi, a component of Eriosoma communities, does not form its own galls but obligatorily usurps those of other species. There were interspecific differences in the timing of gall formation and the spatial distribution of galls. Nevertheless E. yangi fundatrices randomly invaded galls of any Eriosoma species and occupied 33%–41% of galls of each species. When more than one E. yangi fundatrix invaded one gall, mortal fights sometimes occurred. Fundatrices of gall-forming species also seemed to take part in such fights. Fundatrices of gall-forming species had a significant tendency to invade galls of a particular species. However, taking account of niche differences among species, invaders apparently entered available galls at random. Apparently E. yangi fundatrices search an extensive range within a branch for galls, while invaders of gall-forming species search a restricted speciesspecific range. The niche relation of gall-forming species in a northern community containing E. yangi were compared with those in a southern community lacking E. yangi. No obvious difference was found between them, suggesting that parasitism by E. yangi has not influenced niche divergence within the Eriosoma community.     

Effect of plant growth regulators and basal media onin vitro shoot proliferation and rooting ofMyrtus communis L.

The influence of macronutrients and growth regulators on in vitro shoot proliferation and rooting of an East Spanish population ofMyrtus communis L. were studied. Preincubation of field material on a medium without mineral salts prevented the browning from phenolic exudates. For multiplication, nodal segments of 5 mm fromin vitro produced shoots were cultured on Murashige and Skoog (MS), Schenk and Hildebrandt (SH) and Heller (H) media (full strength or diluted to 1/2 or 1/4), with 6-benzylaminopurine (BAP) at concentrations 4.4, 13.3 and 22.2 ΜM or kinetin (K) at concentrations 4.7, 14.0 and 23.2 ΜM. The optimum shoot proliferation was on quarter-strength MS medium with 4.4 ΜM BAP, whereas the maximum number of nodal segments was produced on half-strength MS medium with 4.4 ΜM BAP. Rooting of shoots was obtained by adding 2.5 – 24.6 ΜM indole-3-butyric acid (IBA) and broad range of macronutrients; Lloyd and McCown (WPM) and Gresshoff and Doy (GD) media both full strength or diluted to 1/2 were optimum. No rooting was obtained in the presence of α-naphthaleneacetic acid (NAA). Acknowledgements: This study was supported by a grant from Conselleria de Cultura, Educació i Ciència de Ia Generalitat Valenciana. The authors are grateful to Man Cannen Perea for her helpful comments.     

Optimization of an improved,efficient and rapid in vitro micropropagation protocol for Petunia hybrida Vilm. Cv. “Bravo”

An efficient protocol for in-vitro propagation of an important ornamental crop, Petunia hybrida Vilm. Cv. “Bravo” was developed. The explants that were used to carry out the experiment were Leaf segments, nodal segments and shoot tips. Nodal segments recorded highest per cent asepsis followed by shoot tips and leaf segments. Asepsis was found to be highest when the explants were sterilized with Fungicide (Carbendazim) 0.02% for the duration of 30 min followed by 0.1% HgCl₂ for duration of 10 min and then ethanol 70% for 10 s. Longer duration of the sterilant treatment showed more necrotic effects on the explants, thus mercuric chloride treatment when given for 5 min proved to be more effective in terms of survival of the explants. Maximum establishment per cent was recorded in Murashige and Skoog (MS) media fortified with BAP (1.5 mg L⁻¹) and IBA (0.5 mg L⁻¹) in shoot tips and nodal segments, i.e. 97.90 and 95.74% respectively. Callus was efficiently induced and developed when PGR amalgamation of BAP (0.1 mg L⁻¹) and 2,4-D (1.5mg L⁻¹) was used. Kinetin at the concentration of 2.0 mg L⁻¹ along with IBA at 0.5mg L⁻¹ recorded highest callus regeneration in both leaf and internodal segment derived callus. Maximum proliferation percent of shoots (97.90%), highest number of shoots (20.50 explant⁻¹) and maximum length of shoot (2.70 cm) was recorded in PGR combination of IBA and BAP both at 0.5 mg L⁻1 concentration level. Rhizogenesis was recorded to be highest in the MS media containing IBA 1.00 mg L⁻¹. Best hardening media which recorded maximum survival per cent 92.50% was noticed on the media formulation comprised of equal ratio of perlite and vermiculite mix, under poly house conditions.     

Variation and Morphogenetic Characteristics of Different Stachys Species during Microclonal Propagation

Morphogenesis of different Stachys species introduced in in vitro culture have been compared. The frequency of altered forms have been demonstrated to be related to the plant genotype. All regenerants of S. sieboldii, which reproduces in vivo only vegetatively, are phenotypically normal, irrespective of the concentrations of plant growth regulators at which they have been obtained. Only changes in isozyme patterns have been observed in the regenerants grown in media containing at least 10 mg/l benzyl aminopurine (BAP); most of these changes are the absence of a particular component of the pattern. The cross-pollinating species Stachys ocymastrum, which typically reproduces by seeds, has yielded morphologically altered forms even in phytohormone-free media; its isozyme patterns often contained a new component. Analysis of the isoperoxidase patterns of regenerants of both Stachys species obtained with the use of high phytohormone concentrations has demonstrated qualitative and quantitative changes suggesting the appearance of somaclonal variants even in the course of plant regeneration directly from nodal segments, bypassing callus formation. Changes have also been found in Stachysplants regenerating from the callus tissue.     

Controlling vitrification of petunia in vitro

Summary Nodal segments from in vitro culturedPetunia hybrida were grown under varying cultural conditions. The origin of nodal explants influenced vitrification. Basal segments formed a higher percentage of vitreous shoots than did the upper nodes. A method was developed for including polyethylene glycol with Gelrite to obtain gelled media of varying water potentials. Media water potential from −0.31 to −1.2 MPa had no effect on controlling the level of vitrification. Gelrite promoted vitrification but GIBCO agar, alone or in combination with Gelrite, reduced its occurrence. Lowering media NH₄ content reduced vitrification, whereas sealing culture vessels with parafilm increased it. As it is now possible to control normal and vitreous plant development inPetunia, this can be used as a model system for studying the physiology and biochemistry of this developmental abnormality.     

Micropropagation of Coleus blumei from nodal segments and shoot tips

A rapid and highly-effective method for micropropagation from nodal segment and shoot tip explants was established for Coleus blumei Benth. Nodal segments and shoot tips were inoculated on MS medium containing 0.7 % agar, 3 % commercial sugar, and different combinations of 6-benzyladenine (BA) with indole-3-acetic acid (IAA), indole-3-butyric acid (IBA) or α-naphthaleneacetic acid (NAA). Hundred percent shoot induction from both explants was achieved on the medium containing BA (2 mg dm⁻³) and NAA (1 mg dm⁻³). Shoot tips were proved to be the better explant in comparison to nodal segments in having high rate of shoot induction and more number of shoots. The same media conditions were found suitable for shoot multiplication. Multiplied shoots rooted best on MS medium supplemented with IBA (2 mg dm⁻³). Micropropagated plants were successfully established in soil after hardening, with 100 % survival rate.     

A protocol for rapid micropropagation of endangered Isoplexis

Summary An efficient protocol for large-scale micropropagation of Isoplexis canariensis (L.) Loud., I. chalcantha Svent, and O'Shan., and I. isabelliana (Webb and Berth.) Masf. (Scrophulariaceae) is reported. Multiple shoots were obtained from shoot tips and nodal segments isolated from seedlings when cultured under varying conditions. Factors such as nutrient media, concentration of growth regulators, and type of induction medium (liquid or solid) strongly influenced shoot proliferation and development. Multiple well-developed shoots were obtained after induction on solid media containing Murashige and Skoog full-strength salts and low cytokinin concentrations. By changing the major salt formulation to half strength and employing liquid media the morphogenic parameters evaluated were affected negatively. Many shoots rooted spontaneously in hormone-free media and plants grew successfully in the greenhouse. Flowering was observed 6 mo. after ex vitro cultures were established.     

Influence of explant source, plant growth regulators and culture environment on culture initiation and establishment of Quercus robur L. in vitro

Suitable cytokinin supplements and culture environments havebeen determined for the initiation and establishment of shootcultures of Quercus robur seedling tissue. Initiation of axillaryshoot development from nodal explants required culture mediumsupplemented with BA (6-benzylamminopurine). The greatest numbersof stem segments for culture proliferation were obtained using1.0 mg I^-1 BA after 56 d culture. The frequency of shoot developmentand subsequent formation of multiple shoots at initiation wasinfluenced by the position of the nodal explant in the seedlingshoot, incubation temperature and daylength. Explants from basaland apical regions, which contained multiple axillary buds,produced the lowest frequencies of axillary shoot developmentand multiple shoot formation, many remained quiescent. Axillaryshoot development was greatest in single nodal explants excisedfrom the midstem positions, elongated regions of the shoot wherenodes were formerly associated with a leaf. Higher temperaturesstimulated shoot formation with greater numbers of stem segmentsfor culture multiplication being obtained from nodal explantsincubated at 25C. Axillary shoot development was promoted innodal explants maintained under daylengths of 16 h or more.Stem segments cut from axillary shoots which developed fromnodal explants were used to establish shoot multiplication cultureson medium supplemented with 0.4 mg I^-1 BA. Shoot formation fromstem segments was greater at higher incubation temperaturesof 25C and 30C. Multiplication coefficients for stem segmentsincreased after one subculture. Key words: Quercus robur, oak, micropropagation, cytokinin, temperature, daylength, rest, quiescence     

Abscisic acid-induced growth inhibition of sweet potato (Ipomoea batatas L.) in vitro

The inhibitory effects of abscisic acid (ABA) on in vitro growth and development of axillary buds from nodal segments of sweet potato (Ipomoea batatas L.) was investigated. ABA at concentrations of 0.01, 0.1, 1.0 or 10.0 mg 1^-1 inhibited axillary bud and root development and subsequent plantlet growth. ABA at 10 mg 1^-1 completely inhibited axillary shoot development but did not affect the viability of cv. Jewel explants over a culture period of 365 days. Transfer of nodal segments cultured for 90, 180 or 365 days from basal medium containing 10 mg 1^-1 ABA to growth regulator-free media resulted in rapid and normal plantlet development. Gibberellic acid at 0.1, 1.0 or 10.0 mg 1^-1 in the presence of ABA at 0.1, 1.0 or 10.0 mg 1^-1 did not counteract the ABA-induced growth inhibition. Although ABA totally inhibited the growth of 6 sweet potato plant introductions at a concentration of 10.0 mg 1^-1, the efficacy of ABA as a suppressant of shoot growth varied with genotype.Abbreviations ABA abscisic acid - GA gibberellic acid - cDNA complementary DNA - PI plant introduction - SE standard error