Interaction of photoperiod and temperature in the control of growth and dormancy of Prunus species

Growth and dormancy induction of seedlings or micropropagated plants of three Prunus species were studied under controlled environment conditions. All the species tested, P. cerasus L. and P. insititia L. (two cultivars each), and P. avium L. were insensitive to photoperiod at high temperature and maintained continuous growth in both 10 and 24-h photoperiods at 21 °C. At lower temperatures, however, growth was controlled by the interaction of photoperiod and temperature, the species and cultivars varying somewhat in their responses. At 9 °C growth cessation was induced regardless of day-length conditions in the plum rootstocks ‘St. Julien A’ and ‘Weito’ as well as in the sour cherry rootstock ‘Weiroot’, whereas in the sour cherry rootstock ‘Gisela 5’ growth cessation took place in short day (SD) only. At intermediate temperatures (12 and 15 °C) growth cessation occurred in SD only in both sour cherry cultivars. In P. avium seedlings on the other hand, growth cessation in SD was only induced at 9 °C, continuous but reduced growth taking place also in SD at all higher temperatures. Growth rates increased progressively with increasing temperature under long day (LD) conditions in all species, and this was associated with increased internode length in LD compared with SD conditions. Production of new leaves was unaffected by photoperiod at high temperature, but was higher in LD than in SD at lower temperatures. After growth cessation at low temperature the plants developed winter buds and became dormant also in LD conditions. These results demonstrate that, like several species of the Pomoidae subfamily of the Rosaceae, these Prunus species are insensitive to short photoperiods at relatively high temperatures. However, the photoperiodic response of the Prunus species is highly temperature dependent, and the transition temperatures for shifts in the photoperiodic response mode vary among the species.     

Antioxidant capacity and phytochemical properties of cornelian cherry (Cornus mas L.) genotypes in Iran

Cornelian cherry (Cornus mas L.) is a naturally growing dogwood species in Arasbaran (East Azerbaijan, Iran). Antioxidant capacity, total anthocyanins, total phenols, ascorbic acid and total flavnoids of a number of selected cornelian cherry genotypes were investigated. The total phenolic and antioxidant activity of methanol extract of cornelian cherry fruits were determined according to Folin–Ciocalteu and DPPH method, respectively. The range of ascorbic acid content of genotypes was 183.25–299.5 mg/100 g fresh weight (FW). Genotype C24 had the highest total antioxidant capacity (82.37) and total phenolic (2695.75 mg galic acid per 100 g FW basis). The highest total anthocyanin was observed in C27 genotype (442.11 mg cyanidin-3-glucoside equivalents/100 g FW). This genotype also had the highest total flavonoid (669 mg catechin per 100 g FW basis). There are linear relationships between the antioxidant capacities with total phenols, total flavonoid and ascorbic acid. But, No statistically significant correlation was observed between antioxidant activity and total anthocyanins. According to Path analysis, the highest direct effect on antioxidant was observed in total flavonoid (0.38). The present study demonstrates the potential of certain cornelian cherry genotypes, notably C24 and C27, for improvement of nutritional value through germplasm enhancement programs.     

The effect of nitrogen source and concentration,medium pH and buffering on in vitro shoot growth and rooting in Eucalyptus marginata

This work examined the effect of nitrogen source and medium buffering on the micropropagation of Eucalyptus marginata Donn ex Sm. The number of shoots was increased when media contained 2-(N-morpholino) ethanesulfonic acid (MES) but this increase was minor and only applied to one of the two clones tested. Highest root production was obtained when the medium contained 7.5 mM nitrogen in a ratio of 2NO₃⁻:1NH₄⁺ and was buffered with 10 mM MES. In the rooting medium the pH was influenced most significantly by the nitrogen source, and then whether the medium was buffered. The media pH remained relatively constant when nitrate was the sole nitrogen source and this was assisted by the addition of 10 mM MES. Lower concentrations (<10 mM) of MES were less effective in buffering media over a four-week culture period in both shoot multiplication and rooting medium.     

Environmental control of growth and flowering of Rubus idaeus L. cv. Glen Ample

Environmental control of the annual growth cycle of ‘Glen Ample’ raspberry has been studied in order to facilitate crop manipulation for out-of-season production. Plants propagated from root buds were raised in long days (LD) at 21 °C and then exposed to different temperature and daylength conditions at varying ages. Shoot growth was monitored by weekly measurements and floral initiation by regular sampling and examination of axillary bud #5. Under natural summer daylight conditions at 60°N shoot growth was nearly doubled at 21 °C compared with 15 °C, while at 9 °C one half of the plants ceased growing and formed flower buds at midsummer. Developing shoots have a juvenile phase and could not be induced to flower before the 15-leaf stage. No significant reduction in induction requirements was found in larger plants. Plants exposed to natural light conditions from 10th August, had an immediate growth suppression at 9 and 12 °C with complete cessation after 4 weeks (by September 7). This coincided with the first appearance of floral primordia. At 15 °C both growth cessation and floral initiation occurred 2 weeks later (by September 21), while at 18 °C continuous growth with no floral initiation was maintained until early November when the photoperiod had fallen below 9 h. The critical photoperiod for growth cessation and floral initiation at 15 °C was 15 h. Plants exposed to 10-h photoperiods at 9 °C for 2–4 weeks had a transient growth suppression followed by resumed growth under subsequent high temperature and LD conditions, while exposure for 5 or 6 weeks resulted in complete growth cessation and dormancy induction. The critical induction period for floral initiation was 3 weeks although no transitional changes were visible in the bud before week 4. When exposed to inductive conditions for marginal periods of 3 or 4 weeks, an increasing proportion of the plants (20% and 67%, respectively), behaved as primocane flowering cultivars with recurrent growth and terminal flowering. It is concluded that growth cessation and floral initiation in raspberry are jointly controlled by low temperature and short day conditions and coincide in time as parallel outputs from the same internal induction mechanism.     

Growth and flowering of Nerine flexuosa alba

N. flexuosa alba is a perennial bulbous member of the Amaryllidaceae and an attractive new ornamental. In the bulb, inflorescence buds are formed periodically under any circumstances which allow growth. The problem was that quite often these buds do not elongate, and desiccate prematurely, so that poor flowering results.Light was found not to be a factor in flowering, neither energetically nor photo-periodically, but temperature turned out to be limiting. Good flowering occurred after growth at temperatures of 9 or 13°C, 17 and 21°C being too high. The combination of 9°C during growth and 21°C during storage resulted in 100% satisfactory flowering and an acceptable bulb growth. Gibberellic acid did not effect flowering.     

Agrobacterium tumefaciens mediated genetic transformation and regeneration of Morus alba L.

An efficient method was established for genetic transformation of Morus alba clone M5 using Agrobacterium tumefaciens mediated gene transfer. Cotyledon explants from in vitro grown seedlings were co-cultivated with disarmed strain LBA 4404 harbouring the binary vector p^BI121 carrying chimeric β-glucuronidase (GUS) and neomycin phosphotransferase (npt II) genes. Maximum transformation frequency of 18.60% was recorded with 48 h of pre-conditioning followed by co-cultivation for the same duration. Expression and presence of transgene was confirmed by histochemical test and polymerase chain reaction. The transgenic plants were micropropagated and successfully acclimatised.     

Effects of temperature and daylength on growth and flowering of roselle, Hibiscus sabdariffa L.

Hibiscus sabdariffa L. was found to show an ambiphotoperiodic reaction, flowering both in short days and in extremely long days, but remaining vegetative (at least at 21–25° C) in a 16 h day. Flowering had a dual effect on growth. When floral induction was strong, lateral buds developed into flowers and the number of branches was proportionally reduced. The first stage of floral induction, however, was accompanied by a decrease of apical dominance. Plants shifted to long days after only a short stay at an inductive daylength, and plants moved to short days after a prolonged stay in long days, formed many more branches and a much greater vegetative mass than plants grown in continuous short days or long days.Plants were already sensitive to daylength in the cotyledon stage. Floral induction was not carried over from short days into long days. After marginal induction, floral buds reverted to vegetative shoots, or aborted and were replaced by a shoot from the axil of a bract.In short days, seedlings form shallowly three-lobed leaves until the generative stage, when only entire leaves are formed. In long days, the leaves are deeply five-lobed, also when the plant flowers.     

Temperature integration of Hederahelix L.: Quality aspects and growth response

Reducing energy use in greenhouses contributes to the profitability of horticulture. Important energy savings can be realized through the use of temperature integration. However, such a greenhouse heating strategy is only acceptable for commercial purposes if there are no adverse effects on plant growth and quality. During this 3-month study, Hedera helix ‘Green Ripple’ and H. helix ‘Shamrock’ were subjected to a day/night temperature regime of 20/20 °C (control) and two treatments with temperature integration over 24 h and 4 d, respectively, based on a DIF of 13.5 °C, maintaining the average temperature at the same level of the control. Temperature treatments resulted in a promotion of stem elongation. After 3 months, shoot length rose up to maximum 37.3% when temperature integration was applied. However, temperature integration reduced total dry weight and particularly root dry weight was negatively affected. In addition, assessments of relative growth rate, shoot extension rate, specific leaf area, total leaf area and pigment concentrations were performed and it was concluded that dynamic temperature regimes with longer integration periods support commercial production of English ivy.     

Root development of Thuja plicata in peat-substitute rooting media

In this study we investigated the potential usefulness of different substrates produced from gorse (Ulex europaeus L.) for propagating cuttings of Thuja plicata ‘Atrovirens’. The gorse was composted by different methods, to produce four types of compost. These composts were then used as such (100% compost) or in mixes with coarse sand and pine bark compost (25% compost, 25% coarse sand and 50% pine bark compost, v/v/v) to prepare eight different substrates. The substrates were compared in cutting propagation trials carried out in a greenhouse, with a standard rooting medium consisting of 25% Sphagnum peat moss, 25% coarse sand and 50% pine bark compost (v/v/v). Cuttings were taken from a garden hedge in March 2003, and comprised shoots of the previous year's growth. The bases of the cuttings were treated with a 0.4% solution of IBA rooting hormone, then inserted into cells filled with the corresponding substrate and placed on a propagation bench. Rooting percentage and visual rooting score were determined in July. The quality of roots was evaluated, as total root length and number of root tips, in July, September and November 2003, by use of a Delta-T Scan system. The rooting success of the cuttings ranged from 75% to 90%, except when the substrate comprised the pure composted gorse, obtained after the shorter period in an enclosed composting system with addition of fertilizer and reuse of leachates. Most of the cuttings in this substrate died and only 4% of the cuttings rooted successfully. Physicochemical characteristics of this rooting medium included very high electrical conductivity, low C/N ratio and high water retention. Addition of coarse sand and pine bark compost to the composted gorse significantly increased the rooting success. The root quality variables differed depending on the substrate considered and date of harvest. The results showed that substrates made from gorse compost are of potential use as a peat substitute for propagating cuttings of T. plicata ‘Atrovirens’. The physicochemical properties of the composted gorse should be determined before its use to establish whether it can be used pure as a substrate for rooting or whether it should be mixed with other substances.     

A comparison of the gelling of isubgol,agar and gelrite on in vitro shoot regeneration and rooting of variety Samsun of tobacco (Nicotiana tabacum L.)

Agar is being used to solidify media for plant tissue culture since long. Both purity and type of agar or gelling agent influence the behaviour and growth of tissues in culture. The study using leaf disc explants of variety Samsun of tobacco compares adventitous shoot regeneration on 0.5 cm × 0.5 cm leaf discs cultured on MSD4X2 medium and rooting on MSO medium gelled with different blends of agar–isubgol, gelrite–isubgol, phytagel–isubgol or isubgol singly. It was found that irrespective of some problems associated with isubgol gel, the maximum number of shoot per explant were recorded on MSD4X2 medium gelled with 7 g/l isubgol. The longest shoots were recorded on MSD4X2 medium gelled with 9 g/l isubgol. Likewise, the highest number of roots were also recorded on MSO medium gelled with 7 g/l isubgol. For a given quantity of a medium, agar, gelrite/isubgol blends are very cheap compared to agar used singly. Moreover, blends of agar/isubgol, gelrite/isubgol gelled at low temperatures indicated safe use of these gels for heat labile substances in genetic transformation or tissue culture experiments. The results emphasized the potential of the isubgol used singly or in combination with agar and gelrite for economic commercial application, replacing the costliest, though not indispensable, gelling agent agar.     

Antioxidant potency of white (Brassica oleracea L. var. capitata) and Chinese (Brassica rapa L. var. pekinensis (Lour.)) cabbage: The influence of development stage,cultivar choice and seed selection

The accumulation of total phenols (TP, Folin-Ciocalteu method) and total flavonoids (TF, colorimetric assay with AlCl₃) and the evolution of antioxidant capacity (FRAP assay, DPPH and ABTS radical scavenging assays) have been monitored in juices of Croatian white cabbage (Brassica oleracea var. capitata) cultivars Vara?dinski and Ogulinski, as well as Chinese cabbage (Brassica rapa var. pekinensis), at various developmental stages. Measurements were performed every four weeks, starting from planting to full maturity, throughout the course of eight months. In the first 8–12 weeks, the TP and TF contents as well as antioxidant capacity increased significantly in all analyzed juice samples and in most even doubled. This rapid increase was followed by a gradual decrease in values derived from all assays, over the course of 12–30 weeks, to the final values which were in all cases lower than the values measured at week 4. The results also point to significant variability in TP and TF contents and antioxidant capacity at the fully mature stage between white and Chinese cabbage juices and between juices extracted from cultivars Ogulinski and Vara?dinski.     

Starch depletion and anatomical changes during the rooting of Castanea sativa Mill. cuttings

Starch depletion during rooting of juvenile chestnut cuttings was examined. A marked depletion occurred in the first 3 days following hormonal treatment; in untreated control cuttings there was no significant effect during the same period of time. Anatomical changes during the rooting-process were also studied. Greater starch depletion following hormonal treatment could provide the energy necessary for the great cell proliferation observed at 3–5 days, the organization of the primordia and the differentiation of the new xylem.     

Artificial cold treatment,gibberellin application and flowering response of kohlrabi (Brassica oleracea L. var. gongylodes L.)

Juvenility, cold requirement and the effect of GA₃-application on flowering have been studied for some cultivars. If present, the juvenile phase was very short. Cold treatment for 8–12 weeks at 4 °C followed by 2 weeks at 10 °C gave flowering in all cultivars. Gibberellin sprays (250 or 500 p.p.m., 3 times) after an incomplete cold treatment promoted bolting and flowering even in the slow-bolting ‘Trero’, having the highest cold requirement.     

Effect of glucose on in vitro rooting of mature plants of Bambusa nutans

A high-frequency in vitro rooting method was developed for Bambusa nutans, one of the economically important bamboos in India. Two clones of approximately 10-year-old B. nutans were used for axillary bud proliferation. The effect of carbohydrate source (glucose and sucrose) and auxins (IAA, IBA and NAA) on the in vitro rooting response was evaluated. Rooting percent, mean number of roots and root length were recorded after 14 days of treatment. Successful treatment (49.0 μM IBA and 88 mM glucose in the induction phase for 3 days followed by MS salts with 88 mM sucrose) was repeated four times each with 100 shoots to ascertain the practical utility of the protocol. Addition of glucose along with 49.0 μM IBA during the root induction phase gave 85% rooting success. Anatomical studies in the nodal regions were conducted to determine the effect of glucose on root primordial development and elongation. It was observed that the presence of glucose in the root induction medium is required to recruit more number of root initials. A simple protocol was developed for the large-scale production of B. nutans, where rooting of microshoots developed from mature tissues is always difficult. This study showed that glucose as carbon source and auxin type IBA is essential for in vitro root formation in the cultures raised from mature tissues.     

Effect of air humidity on the growth and morphology of Hydrangea macrophylla L.

Hydrangea macrophylla cv. Leuchfeuer is grown in the greenhouse under two different conditions of relative humidity (vapour pressure deficits (vpd) of 1.6 and 0.6 kPa). The relative humidity does not affect the initiation or the release of new pairs of leaves. However, it modifies the size of the plant and the total leaf area. After 79 days of growth, a decrease in the relative humidity from 80% to 50% leads to a 38% decrease in height growth and a 30% decrease in leaf growth. The effect of relative humidity on the growth of H. macrophylla influences the management of the size of the plant and, therefore, the quality of the product marketed. It is likely that it will have an effect on floral development as well.     

Effects of forcing,etiolation and indole butyric acid on rooting of cuttings of Artocarpus heterophyllus Lam.

Rooting of cuttings of jackfruit (Artocarpus heterophyllus Lam.) has been successfully induced through forcing of shoots, etiolation and application of indole butyric acid (IBA) under mist spray. Maximum rooting (84%) and maximum survival (50–75%) were obtained with the forced and etiolated shoots treated with 5000 mg/l IBA. The next best treatment was the forced and etiolated shoots treated with 10 000 mg/l IBA, which was somewhat similar to forced, non-etiolated shoots treated with 5000 mg/l IBA. In the control without IBA no success was obtained even under forcing and etiolation.     

Germination of Passiflora mollissima (Kunth) L.H.Bailey, Passiflora tricuspis Mast. and Passiflora nov sp. seeds

Passiflora mollissima, Passiflora tricuspis and Passiflora nov sp. are three passion fruit species occurring in Bolivia. Germination percentages and rates were determined for 11 different treatments. Per species, germination of 100 seeds was monitored every 3 days, during 90 days. Germination started after 9 days and 50% of final germination was reached within a month or less. Successful, recommended methods for P. mollissima are removing the basal point of seeds (27% germination) or removing the basal point in combination with pre-soaking seeds for 48 h in 50 ppm GA₃ (18%). Pre-soaking seeds for 24 h in 400 ppm GA₃ (42%) and removal of the basal point in combination with pre-soaking seeds for 48 h in 50 ppm GA₃ (36%) are suggested methods to improve germination of P. nov sp. Removing the apical point of P. tricuspis seeds resulted in maximal germination (57%). No unique treatment gave satisfactory results for the three species tested. Exogenous dormancy, probably a combination of mechanical and chemical dormancy is present in the three species studied. Presence of physical dormancy was found in P. mollissima.     

Temperature effects on dormancy,bud break and spear growth in asparagus (Asparagus officinalis L.)

Summary

The effects of the length of chilling, chilling temperature and growing temperature on dormancy of asparagus crown buds and subsequent rates of spear growth were examined. The results showed that prior chilling enhanced bud break at low growing temperatures and stimulated the growth of spears.Thus, chilling should facilitate commercial production by hastening bud break and spear growth rates at lower temperatures. If sufficient chilling was given, the minimum temperature for rapid bud break was approx. 12.5°C for ‘Rutgers Beacon’ and ‘Jersey Giant’, and around 10°C for ‘UC 157’ and ‘Apollo’. The optimum chilling temperature appeared to be closer to 5°C than to 10°C or 2°C for ‘Rutgers Beacon’ plants grown at 12.5°C. Increasing the growing temperature had a significant effect on the relative spear growth rate (RSGR) in all cultivars. Prior chilling had no effect on the RSGR for ‘Dariana’ and ‘Apollo’; but, for ‘UC 157’, chilling plants at 5°C for 5 or 10 weeks increased growth rates at 12.5°C and at 20°C. These results demonstrate that release of bud dormancy and spear growth rates depended not only on the growing temperature, but also, at least in some cultivars at some temperatures, on the duration and temperature of chilling during the previous Winter.     

Effect of some growth regulators on sex expression of Momordica charantia L.

Gibberellin (GA), benzyladenine (BA), and maleic hydrazide (MH) promoted formation of female flowers in Momordica charantia L. GA was most effective. Low concentration of 2-chloroethyl trimethyl ammonium chloride (CCC) showed femineity, whereas high concentration showed a masculinizing effect. The effects of different concentrations of GA, BA, MH and CCC on flowering and sex expression are discussed. GA should not be considered as a general male sex hormone for all cucurbits.     

Preservation of cuttings of Rhododendron obtusum Planch., R. ponticum L. and R. simsii Planch.

Owing to lack of space or time, cuttings of rhododendrons cannot always be rooted at the moment they are ready for propagation. We investigated how cuttings could be cold stored until the time they are to be rooted. The cuttings can best be preserved at temperatures just above freezing. At higher temperatures the period of successful storage is shortened. The greatest hazard is Botrytis cinerea attack, but this can be prevented by a prophylactic spray with benomyl. More lignified cuttings can be preserved longer than more herbaceous ones. The methods described can be used for storing cuttings of Rhododendron obtusum, ponticum and simsii hybrids.