Growth Regulator Treatments Research Articles

Morphological and anatomical modifications in winter barley culm after late plant growth regulator treatment

One of the major factors limiting yield production in barley (Hordeum vulgare L.) has been its poor straw strength. Consequently, a greater stiffness of the upper part of the culm was desirable. So, a late application of plant growth regulator could be interesting for weak-strawed barley cultivars. The objective of these experiments was to investigate the effect of a late application of a combination of chlormequat chloride (2-chloroethyl-trimethyl-ammonium chloride), ethephon (2-chloroethyl phosphonic acid) and imazaquin (2-[4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl] nicotinic acid) on the morphological and anatomical characteristics of barley main stems. In a field trial and a greenhouse experiment, a foliar treatment was applied to a two-row winter barley (Labéa) at growth stage 7 (Feekes, 1941). Measurements of plant height, internode lengths, dry weights and microscopic examination of cross-sections of the top three internodes were made at anthesis. The plant growth regulator (PGR) decreased significantly plant height by reducing the length of the upper internodes. The PGR did not modify the total weight of the upper internodes, but induced an increase of the dry weight per unit length of the main stem. The shortening of the internodes combined with the higher density of the tissues contributes to the stiffness of the stem. This was confirmed by anatomical studies which showed the modifications of the supporting tissues. The application of the plant growth regulator did not affect grain yield.

In vitro propagation of cauliflower, Brassica oleracea var. botrytis for hybrid seed production

Methods for obtaining heterotic F1 and maintaining purebred lines for breeding of Brassica oleracea are limited by absence of male sterile lines and occurrence of inbreeding depression, respectively. The use of vegetative (stem, petiole, leaf, leaf rib) and floral (peduncle, pedicel, flower bud, curd) explants of cauliflower to regenerate purebred lines for crossing were examined. Of four growth regulator treatments and explant types used, best results were obtained with curd explants on MS medium with 6-benzyladenine (cytokinin) and gibberellic acid. Although 6-benzyladenine alone promoted formation of shoots in floral explants, both 6-benzyladenine and α-napthaleneacetic acid were required for vegetative explants. Use of α-napthaleneacetic acid, however, often increased callus formation. These culture techniques to maintain purebred regenerated plants will complement newly-derived nuclear-based male sterile lines obtained by the introduction of antisense copies of the gene BcpI, which is required for pollen fertility.

EFFECT OF SEED TREATMENT WITH PLANT GROWTH REGULATORS ON BHENDI (Abelmoschus esculentus L.,) GROWN UNDER SODIC SOIL CONDITIONS

Field experiment conducted with seed treatment of plant growth regulators indicated that gibberellic acid at 50 ppm is the most effective treatment for bhendi under sodic soil conditions. This treatment recorded the highest germination, seedling establishment.total DMP. harvest index.number of fruits per plant and yield of fruits. Gibberallic acid at 50 ppm recorded the highest vegetable yield of 15.7 t/ha followed by GA 75 ppm with 14.8t/ha. The control recorded only 8.07 t/ha of yield.

Effects of Plant Growth Regulators Applied as Sprays or Media Drenches on Forcing of Dutch-grown Bleeding Heart as a Flowering Potted Plant

Two experiments were conducted to determine the effects of applied ancymidol, chlormequat, daminozide, paclobutrazol, and uniconazole on early spring (March) and late (May) spring forcing of Dutch-grown Bleeding Heart [Dicentra spectabilis (L.) Lem.] as a flowering pot plant. Most of the plant growth regulator (PGR) treatments delayed flowering, however, the average time to flower after planting was from 17 to 21 days for untreated plants and delays were only 3 to 6 days with PGR treatments. Thus, the effect is not important commercially. Acceptable plant quality and height control not only at flowering but also 14 days later was obtained with two sprays of 3000 mg·L-1 (ppm) daminozide or two sprays of 50 mg·L-1 paclobutrazol. Uniconazole reduced total plant height, however, because the inflorescence did not elongate, plant quality was greatly reduced. Most ancymidol sprays were phytotoxic producing a chlorosis of the leaf margins. Media drenches of ancymidol or chlormequat did not control total plant height. Sprays and media drenches of ancymidol, daminozide, paclobutrazol, and uniconazole produced plants with a very deep green leaf color, but chlormequat did not. The total number of shoots per tuberous root, the number of shoots with flowers, and stem strength were not significantly affected by PGR treatments. If the tuberous roots have been properly cold treated, they initiate growth rapidly after planting. Thus, the first PGR spray must be applied immediately after shoot growth is initiated, which was 6 to 8 days after planting, followed by a second spray 5 days later. Two applications are necessary because of uneven shoot emergence and growth from the tuberous roots.

Direct rooting and hardening of tea microshoots in the field

Micropropagation of tea (Camellia sinensis (L.) O. Kuntze) has been widely attempted but commercial exploitation of this method is limited by heavy losses during the hardening procedures. In the present study, optimization of time of harvesting (spring and early summer) of microshoots, shoot size, soil pH (4.0–6.4), plant growth regulator treatment (IBA; 500 mg l-1, 30 min) CO2 (9.09/10×10−5 mol l-1 to 10.22/10×10-5 mol l-1 and 20/11×10−5 mol l-1 to 80/13×10−7 mol l-1) enrichment and light (15 μ mol m-2 s-1) conditions in specially designed hardening chambers, made a significant impact on the percent of success for hardening. Following the standardized procedure, up to 71.6% root induction and 73% survival could be achieved. Successful field transfer was also accomplished.

Micropropagation of juvenile sycamore maple via adventitious shoot formation by use of thidiazuron

Zygotic embryos of sycamore maple (Acer pseudoplatanus) were dissected into plumule, hypocotyl and radicle sections. The segments were placed on MS medium containing 1 μM 6-benzyladenine (BA) and/or 0.02 μM to 0.1 μM thidiazuron (TDZ). Hypocotyl and plumule explants produced callus, adventitious buds and shoots with increasing plant growth regulator concentrations. Hypocotyls produced more, but smaller shoots compared to plumule segments. Subculturing excised shoots and calluses on Murashige and Skoog (MS) media with 1 μM BA and/or 0.04 μM TDZ led to continuous production of shoots. The best proliferation capacity occurred with 0.04 μM TDZ and 1.0 μM BA, both shoots and calluses. This combination showed a stimulatory effect also on length of newly formed shoots. Calluses performed generally better compared to shoot explants independent of growth regulator treatment. Excised shoots 2 to 3-cm-long were successfully rooted on MS media either with or without growth regulators (123 μM IBA pulse) followed by transfer to the greenhouse.

Modelling pesticide residues on greasy wool: surveys of the insect growth regulators triflumuron and diflubenzuron

Surveys have examined the relationship between louse and flystrike treatments on farms and the resulting residues of insect growth regulators on greasy wool. These results have been summarised using a model of the on-farm survey data. The model estimated the amount of chemical taken up by the wool at application. This was based on experimental breakdown rates of these insecticides on wool determined in controlled trials. The data indicated that the backliner, triflumuron, when used off-shears within 24 h of shearing, was normally applied at slightly higher than the recommended rate on-farm and left an average residue of 30 mg/kg greasy wool at the following shearing 12 months later. Diflubenzuron, applied by dipping or jetting, was usually applied at lower than the recommended rates, and left an average residue of 40 mg/kg on the wool at shearing 12 months later. When treatment was applied to very short wool (<3 weeks after shearing) the residue was only about 20 mg/kg, but when applied at later times after shearing the residue at the following shearing was not closely related to the time of treatment. The model can be used to estimate the expected residue level and likely range of results from most standard insect growth regulator treatments. This will improve advice to producers so most can meet specified industry standards.

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N1-(2-chloro-4-pyridyl)-N2-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10(-5) m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Key Words. Maize-Putrescine-4-PU-30-ABA-Drought

Adventitious root initiation, plasticity, and response to plant growth regulator treatments of seedling, juvenile, and adult Elaeocarpus hookerianus plants

We characterise the propagation success of cuttings from juvenile and adult plants of the New Zealand endemic tree Elaeocarpus hookerianus, and describe the response of seedling, juvenile, and adult plants to various environmental and plant growth regulator treatments. Unexpectedly, more adult cuttings formed roots than juveniles when cuttings were taken during winter, but this was reversed when cuttings were taken during summer. Juvenile plants displayed more variability in leaf properties in response to shaded or glasshouse environments, and to gibberellic acid, benzyladenine, or paclobutrazol treatments than seedlings or adult plants. Juvenile plants displayed larger episodic changes in internode length along the vertical axis than seedling or adult plants. No substantial maturation of juvenile plants or rejuvenation of adult plants was observed following any of the treatments. Age of the shoot appeared to be more important than the size of the plant for control of the transition between juvenile and adult phases, and for the expression of morphological and physiological properties characteristic of each on‐togenetic phase.

In Vitro Germination of Native Terrestrial Orchids

Scarification treatments (a control, a 10-minute vacuum, or a 1.5-minute ultrasound), different media (modified Norstog and Van Waes) and growth regulators [benzyladenine (BA) at 0, 1, 1.5, or 2 mg·L-1 and 6-(r,r-dimethylallylamino)-purine riboside (2iPR) at 0, 1, 1.5 or 2 mg·L-1] were used in combination to increase seed germination of Cypripedium calceolus var. parviflorum. Seeds treated with ultrasound had higher germination (58.0%) than those treated with vacuum (27.4%) or controls (19.2%). Germination rates increased with 2iPR level and reached a maximum between 1.5 and 2 mg·L-1. Seeds on Van Waes medium, which were not transferred to fresh medium after germination, had a severe browning problem causing many protocorms to die. Those on Norstog medium continued to grow into seedlings with less browning. Germination rates of Calopogon tuberosus × Calopogon `Adventure' and Liparis liliifolia were determined on the different media and growth regulator treatments. Multiple shoots of Calopogon developed from single seeds on media containing growth regulators. Flower buds formed in vitro on Calopogon in media containing 1 mg·L-1 or higher BA 5 months after germination. L. Iiliifolia seeds in Norstog medium had a higher proportion of germination than those in Van Waes medium.

Production of doubled haploids in triticale (×Triticosecale Wittm.) by means of crosses with maize (Zea mays L.) using picloram and dicamba

AbstractThe aim of the present study of triticale × maize crosses was to find an appropriate growth regulator treatment to improve the yield of triticale haploids and the subsequent production of doubled haploids. The growth effect in unpollinated ovaries of triticale was examined after treatment with 1000 mg/1 indole‐3‐acetic acid (IAA) or 100 mg/1 solutions of the following auxin analogues: 2,4‐dichlorophenoxyacetic acid (2,4‐D), 3,6‐dichloro‐o‐anisic acid (dicamba), 4‐chloro‐o‐tolyloxyacetic acid (MCPA), phenylacetic acid (PAA), 4‐amino‐3,5,6‐trichloropicolinic acid (picloram) and 2,4,5‐trichlorophenoxyacetic acid (2,4,5‐ T), respectively. Dicamba stimulated growth of the ovaries significantly more than picloram and both stimulated more growth than the other growth regulators tested. Neither dicamba nor picloram induced embryo development in unpollinated pistils. Dicamba and picloram solutions, at concentrations of 25, 50, 75 and 100 mg/1, were subsequently applied to pistils of triticale pollinated with maize. On average, between 17.1 and 21.5 embryos/100 fiorets were excised after treatment with 75 or 100 mg/1 solutions of picloram or dicamba but the concentrations of 20 and 50 mg were less effective. The frequencies of excised embryos did not differ between genotypes. Seventy‐six green haploids were obtained from 100 embryos rescued in vitro on the 190–2 and modified B5 media, the first medium being superior. The plants were subjected to colchicine treatment at the 3–4 tiller stage. Out of 68 plants brought to maturity, 25 exhibited fertile sectors. In comparison with previous studies, picloram and dicamba significantly improved the efficiency of the triticale × maize crossing. The low dependence on the mother germplasm makes triticale × maize crossing an efficient alternative to the androgenetic methods of doubled haploid production in triticale.

Optimizing Graft Union Formation between Sweetpotato (Ipomoea batatas) and Bush Morning Glory (Ipomoea carnea ssp. fistulosa) as a Prelude to Chimera Development

Bush morning glory (Ipomoea carnea ssp. fistulosa) and ornamental sweetpotato (Ipomoea batatas `Blackie') were grafted using various procedures. Lanolin pastes containing 3% BA, 3% NAA, and a mixture of 3% BA/3% NAA were tested as a means of promoting adventitious shoot development at the graft union. Excellent “take” was obtained with all graft types tested. The growth regulator treatments resulted in marked differences in callus formation at the wounded graft union. Lateral shoot development below the graft union also was affected by the growth regulator treatments. The highest quantity of callus was formed using the mixed paste, while BA enhanced lateral shoot formation below the union. Results indicate that in-vivo grafting of these two species may not be the best procedure for obtaining interspecific chimeras.

Effects of AVG, NAA, Ethephon, and Summer Pruning on Preharvest Drop and Fruit Quality of `McIntosh'

Ethylene production increases dramatically during maturation and ripening of `McIntosh' apples, frequently resulting in preharvest drop and accelerated fruit softening. As harvest approaches, commercial growers must balance the need for color development with minimizing fruit softening and drop. The effects of plant growth regulators and summer pruning on this balance were evaluated in this study. Treatments were applied to trees in the Mid-Hudson in 1995 and 1996 and a subset of growth regulator treatments was applied in the Champlain Valley in 1996. NAA (naphthalene acetic acid) significantly reduced drop on only one sample date in only one of the three trials. Ethephon (2-chloroethylphosphonic acid) at 150 ppm plus 10 ppm NAA, accelerated ripening and permitted harvest before substantial drop occurred, but earlier harvest resulted in smaller fruit size. AVG (aminoethoxy vinyl glycine) at 124 gram a.i./ha, on otherwise untreated trees, significantly delayed drop compared to the controls in two of three trials and resulted in better fruit firmness out of storage. Use of ethephon on AVG-treated trees significantly enhanced red color but also accelerated drop, although drop was reduced compared to ethephon only treatment. Late summer pruning significantly accelerated red color development, drop and ripening in both years. Pruning 16 Aug. 1996 significantly accelerated drop compared to pruning 1 Aug. 1996. Combining AVG application and pruning on 16 Aug. 1996 resulted in improved color without increasing drop compared to controls.

Effect of Pot Size and Timing of Plant Growth Regulator Treatments on Growth and Tuber Yield in Greenhouse-Grown Norland and Russet Burbank Potatoes

The effects of pot size, timing of the applica- tion of paclobutrazol (PTZ) and gibberellic acid (GA3), and the counteractive effect of these two compounds on growth and tuber yield of greenhouse-grown Norland and Russet Burbank potatoes were investigated. Plants were grown either in 1.5-liter pots (15 cm deep) or 3.0- liter pots (18 cm deep) and received a foliar application of either 1.5 mM PTZ or 9◊1 0 ˛3 mM GA3 at early or late stolon initiation. Some plants that had been foliar treated with 1.5 mM PTZ at early stolon initiation were foliar treated wit h9◊1 0 ˛3 mM GA3 at late stolon initiation. PTZ reduced haulm length in both cultivars significantly, particularly when the treatment was applied at early sto- lon initiation, but the late treatment reduced haulm length only when growing in 3.0-liter pots. Irrespective of the timing of treatment, GA 3 increased haulm length in Nor- land growing in both pot sizes, but the treatment in- creased haulm length in Russet Burbank only when ap- plied at late stolon initiation. GA 3 applied after PTZ did not overcome the growth-inhibiting effect of the PTZ treatment. The PTZ treatment effectively increased us- able tuber number/plant (UTN) in Norland, but PTZ had no effect on UTN in Russet Burbank. PTZ reduced us- able tuber weight/plant (UTW) only in Norland growing in 1.5-liter pots. By contrast, GA3 increased UTN only when treated at late stolon initiation of 1.5-liter pot- grown Norland, whereas the same treatment was effec- tive when applied only at early stolon initiation for Rus- set Burbank. For Norland, the increase in UTN by early applied PTZ was reduced by the subsequent application of GA 3 . The use of 3.0-liter pots for minituber produc- tion in both Norland and Russet Burbank appears to have no advantage over growing in 1.5-liter pots, particularly when PTZ or GA3 is used to enhance tuberization.

Somatic embryogenesis and plantlet regeneration from immature and mature tissues of sweetgum ( Liquidambar styraciflua)

Source tree, explant developmental stage and plant growth regulator treatments were tested for their relationship to induction of somatic embryogenesis from different explanted tissues of sweetgum ( Liquidambar styraciflua), a common hardwood tree of the southern US. Induction of indirect somatic embryogenesis from staminate inflorescence explants was related to all three independent variables. The highest induction frequencies were obtained from the least elongated inflorescences cultured on medium with 0.01 or 0.1 mg/l thidiazuron. While inflorescence explants from eight of nine source trees yielded embryogenic cultures, two trees were the source of the majority of the embryogenic cultures. Conversely, induction of direct somatic embryogenesis from seed explants was only related to fruit collection week, an index of explant developmental stage, with more immature seeds giving a higher frequency of induction than mature seeds. Culture on medium with 0.5 mg/l or 3 mg/l 2,4-D induced embryogenesis from seed explants. Proembryogenic masses (PEMs) derived from inflorescence tissues and seed tissues produced somatic embryos when transferred to basal medium supplemented with activated charcoal. Germination and conversion frequencies of the somatic embryos were not related to cold pretreatment. Germination frequency, which ranged as high as 90%, varied significantly among clones, while conversion frequency, with a maximum of 60%, did not.

Effect of some plant growth regulator treatments on apple fruit ripening

The activity of IAA oxidase (IAAox), peroxidases (POD), and polyphenoloxidases (PPO), as affected by different pre-harvest growth regulator treatments (ABA, AVG, NAA, PDJ), was determined in on-tree ripening apples (cv. “Golden Delicious”) before and during the ethylene climacteric. The production of ethylene was inhibited by AVG and delayed by NAA, whereas ABA and PDJ treatments caused, in the on-tree remaining fruits, a marked fruit drop and a decrease or a slight increase in ethylene levels respectively. While all treatments reduced POD activity, jasmonate increased IAAox and PPO activity. The inhibitory effect of NAA on all enzyme activity seems related to interference with C2H2 action or to a reduced sensitivity of the fruit abscission zone tissues to the hormone. The observed high fruit drop induced by ABA treatment made it impossible to detect differences in enzyme activity. AVG-treated fruits showed no substantial effects on IAAox and PPO activity in comparison to the control, a finding that seems to be related to a delay in all senescence processes caused by the very low level of the inhibited ethylene production. In control fruits IAAox activity increased during the initial ripening stages and decreased thereafter, POD activity increased throughout ripening and PPO showed little variation.

In vitro morphogenetic responses of mature wheat embryos to different NaCl concentrations and growth regulator treatments

AbstractCallus cultures were initiated from mature excised embryos of winter wheat on Murashige and Skoog (MS) medium supplemented with either 0, 3, 6 or 9g/l NaCl and various combinations of growth regulators. Callus induction rates were virtually 100% on every medium used, while the growth of calli during the induction phase was retarded at higher NaCl concentrations. Application of NaCl and auxin at high concentrations during the induction and proliferation phases strongly inhibited shoot induction. In addition, a competition between root induction and shoot induction was clearly observed. Conversely, rhizogenesis was not significantly decreased under saline conditions and was actually favoured at high NaCl (≥6 g/1) concentrations, especially when 2,4‐D was used as the only auxin for callus induction. Roots induced at lower NaCl levels were significantly longer, thinner, lighter‐coloured and had fewer hairs than roots induced on 6 or 9 g/1 NaCl. Roots induced on NaCl‐free medium also had fewer but larger cortex parenchymatic cell layers and a wider stele compared with roots induced on the highest NaCl level. The best plant regeneration (simultaneous root and shoot formation) rates were observed when calli were induced on 2 mg/1 2,4‐D and subcultured on 1 mg/1 NAA and 3 g/1 NaCl.

Effect of a plant growth regulator regime on internode length and weight of tillers in conventional and hybrid rye and the impact of nitrogen on crop performance

The effect of nitrogen and a plant growth regulator regime (chlormequat chloride followed by 2-chloroethylphosphonic acid) on the crop performance of a hybrid (cv. Luchs) and a conventionally bred winter rye (cv. Sentinel) were investigated in two field experiments each year between 1993 and 1995 at Winchester, UK. Internode length and dry weight/unit length of internodes was measured in order to assess the effect of the growth regulator regime on stem structure. Grain yields were 15% higher in the hybrid Luchs than in Sentinel. With high levels of applied nitrogen, both cultivars lodged in all seasons and this was most severe in 1994 when 88% of the crop lodged in Sentinel and 52% in Luchs. Plant growth regulator treatment consistently reduced lodging but did not eliminate it. Reductions in lodging were not always associated with an increase in grain yield. In the hybrid cultivar, the growth regulator treatment reduced yield in 1993 and 1995 when 2-chloroethyl-phosphonic acid was applied at GS49 and GS39 respectively, but increased yield in 1994 when applied at GS37. Growth regulator consistently reduced stem length, and the percentage reduction in length of the individual internodes within the stem was strongly influenced by the timing of the 2-chloroethylphosphonic acid component of the PGR treatment. Growth regulator reduced internode lengths by up to 25% in Sentinel and 35% in Luchs, and this was associated with reductions in the dry weight of internodes by up to 32% in Sentinel and 38% in Luchs. Consequently, dry weight/unit length of the stem was not increased by growth regulator treatment. Yield reductions in Luchs following growth regulator treatment may have been due to reduced stem reserves which have been associated with tolerance of stress in rye. Both cultivars were highly responsive to nitrogen. Economic optima varied from season to season, but they ranged over three years, from 175–273 kg/ha nitrogen, and were greater than the currently recommended application rates. Crop lodging increased with increasing nitrogen rate even when plant growth regulator was applied and yield penalties from lodging would have been high, if weather conditions during grain maturity had been unfavourable.

Transplanted maize (Zea mays) for grain production in southern England. III. Effects of plant growth regulator treatments on maize transplant morphology

Maize kernels were soaked for 16 h in solutions containing the growth regulators BAS 106.W at 40 or 80 mg/l, PP333 at 80 or 160 mg/l, or BNO 0184 at 100 or 150 mg/l. The plant growth regulator (PGR)-treated kernels and water-soaked controls were sown in planting trays, and seedling transplants were raised in a glasshouse for 24 days. When they were planted in the field, the PGR-treated plants were significantly shorter than controls, with average plant heights (measured from soil level to uppermost leaf collar) of 4·7 cm (BAS 106.W, 40 mg/l), 3·7 cm (BAS 106.W, 80 mg/l), 6·1 cm (PP333, 80 mg/l), 8·0 cm (PP333, 160 mg/l), 6·4 cm (BNO 0184, 100 mg/l), 7·1 cm (BNO 0184, 150 mg/l) and 11·0 cm (controls). The dwarfing of PGR-treated transplants was mainly due to shortened leaf insertions of the lower leaves. Shoot weights were little affected by PGR-treatment, since decreased plant heights were partly compensated for by thicker stems and broader leaves. PGR effects on leaf numbers were negligible. At crop maturity, PGR-treated plants and controls showed similar grain weights and harvest indices. A partial leaf removal treatment at planting using untreated seedlings was associated with rapid crop establishment in the field and like the PGR treatments, it had no significant effect on final yield. It is suggested that a PGR-treatment with a short term dwarfing effect would facilitate the production and handling of maize seedling transplants and may improve establishment and early growth in the field.

Direct Shoot Regeneration from Vaccinium pahalae (Ohelo) and V. myrtillus (Bilberry) Leaf Explants

Ohelo (V. pahalae Skottsb.) and bilberry (V. myrtillus L.) shoots were regenerated via direct organogenesis from whole leaves and leaf sections and also from hypocotyl explants of bilberry. Explants preincubated for 1 to 2 weeks in darkness yielded ≈75% regeneration frequencies and the highest number of regenerating shoots/explant on TDZ-supplemented media (0.9 to 2.7 μm). When 2iP or zeatin were substituted as the cytokinin source, frequencies of regeneration and shoot productivity were significantly lower. Explants held under constant illumination (no dark pretreatment) had significantly lower regeneration frequencies in all tested cytokinin-supplemented media. 2,4-D stimulated callus formation, but did not support regeneration from vegetative explants. Cells from callus and suspension cultures did not exhibit regeneration in any of the media that supported organogenesis from leaves. Regenerants were successfully micropropagated, although callus formation caused by zeatin and high 2iP levels interfered with shoot proliferation. Zeatin induced hyperhydricity in shoots from both species, but more severely in ohelo. Ex vitro rooting after treatment with 4.9 μm IBA or 5.4 μm NAA was 95% and 60% successful for bilberry and ohelo, respectively, and plants were readily acclimatized after an interval in a fog chamber. Bilberry microshoots also rooted in vitro in the absence of growth regulator treatment. Chemical names used: 1H-indole-3-butanoic acid (IBA); N-(3-methyl-2-butenyl)-1-H-purine-6-amine (2iP); 6-furfurylaminopurine (kinetin); 1-naphthaleneacetic acid (NAA); thidiazuron=1-phenyl-3-(1,2,3-thiadiazio-5-yl)urea (TDZ); 2,4-dichlorophenoxyacetic acid (2,4-D); 6-(4-hydroxy-3-methylbut-2-enylamino) purine (zeatin).