Prohexadione-calcium affects growth and flowering of petunia and impatiens grown under photoselective films

The response of petunia (Petunia x hybrida Vilm.-Andr. ‘Countdown Burgundy’) and impatiens (Impatiens wallerana Hook ‘Accent Orange Tempo’) to Prohexadione-calcium was evaluated under a clear and a far-red light absorbing greenhouse (A_FR) film to investigate the dosage effect of Prohexadione-Ca and to determine if it can overcome the flowering delay under FR deficient greenhouse environments. Prohexadione-Ca reduced stem elongation of petunia and impatiens under A_FR and clear films when applied 3 weeks after germination. Late applications were less effective. In both crops, main stem length decreased in a quadratic pattern as the concentration of Prohexadione-Ca increased. Under both films, 50–100 mg l⁻¹ Prohexadione-Ca resulted in ≈30% shorter petunia plants. Greater concentrations (500 and 1000 mg l⁻¹) resulted in excessively short plants (over 70%). Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis of petunia by 8 and 3 days under the clear film and the A_FR film, respectively during less inductive photoperiods but had no effect during inductive photoperiods. In impatiens, Prohexadione-Ca at 100 mg l⁻¹ delayed anthesis over 10 days under clear or A_FR film. Greater concentrations (200 and 300 mg l⁻¹) inhibited flowering of impatiens. Prohexadione-Ca treatments significantly affected flower color development. Untreated petunia plants had dark burgundy flowers. Prohexadione-Ca treatment increased L*, a*, and C* values and decreased hue angle indicating that the flowers were faded. Flowers of untreated impatiens plants were bright orange color. Prohexadione-Ca at 100 mg l⁻¹ increased L* value and decreased a*, b*, and C* values indicating that significant petal fading had occurred. Flowers of treated plants were nearly white under both films. Although effective in height control, loss of color would be a major limitation to the use of Prohexadione-Ca on flowering crops.     

Environmental factors affecting flowering of rice flower (Ozothamnus diosmifolius,Vent.)

Rice flower (Ozothamnus diosmifolius, Vent.), native to east Australia, is a spring flowering perennial shrub. It is a new cut flower plant, recently introduced into cultivation in Australia and in Israel. Its response to environmental conditions, which affect growth and flowering, are not yet known. The purpose of the present study was to evaluate the effects of growth temperature, photoperiod and total solar energy on flowering. Experiments were conducted with plants of the cv. Cook’s Snow White. Plants were grown in three cycles under controlled conditions in the phytotron, at four day/night temperature regimes: 17/9, 20/12, 23/15 and 26/18°C. Two photoperiods — short day (SD) of 10 h natural day light and long day (LD) of 10 h natural light plus 10 h incandescent light — were employed. High temperatures enhanced vegetative growth but blocked flowering under both LD and SD. Under medium–moderate temperatures plants were absolute LD plants and did not flower under SD conditions. Under lower temperatures plants flowered under both LD and SD, but SD delayed flowering. High total solar radiation under LD did not affect flowering time but greatly promoted the number of flowering stems.     

Flowering of Primula malacoides in response to photoperiod and temperature

Primula malacoides Franch. ‘Prima Lilac’ was grown at 16 or 20 °C in combination with short days (SD, 8 h) or long days (LD, 16 h). In addition to uninterrupted growing conditions, plants within each temperature were moved at weekly intervals to the other photoperiod and left until termination. Temperature, but not photoperiod, significantly affected the rate of development from start of treatments (51 days from seeding) to 2 mm visible flower bud (VB). At 16 °C, VB averaged 30 days and at 20 °C, 48 days. Time to flower (first horizontal petals) at 16 °C increased from 56 to 64 days as SD increased from 1 week to continuous conditions while LD decreased time to flower from 64 to 56 days. Time to flower at 20 °C varied from 73 to 87 days with additional SD exposure resulting in slower and LD in faster flowering. These observations of the flowering response in ‘Prima’ are contrary to the photoperiodic classification of P. malacoides as a SD plant.     

The temperature and photoperiod regulation of flowering and runnering in the strawberries,Fragaria chiloensis,F. virginiana,and F. x ananassa

The temperature and photoperiod interactions of a number of elite genotypes of Fragaria virginiana, F. x ananassa, and F. chiloensis were studied in a series of growth chamber experiments. Several parameters were evaluated including: (1) the critical day-length (CDL) for flowering of short day (SD) genotypes under 8, 9, 10, and 11 h days at 18 °C, (2) the floral and runnering response of single and multiple cropping genotypes under 8 and 16 h days at 18 °C, and (3) the effect of temperature on flower bud formation in day-neutral (DN) genotypes held at 18, 22, 26, and 30 °C under 12 h day-lengths. The same number of flowers were initiated under 15 and 30 day induction periods, regardless of photoperiod. Frederick 9, LH 50-4 and RH 30 (F. virginiana), ‘Aromas’ and ‘Tribute’ (F. x ananassa) and CFRA 0368 of F. chiloensis flowered under both long days (LDs) and SDs; while Eagle-14 (F. virginiana), ‘Fort Laramie’ and ‘Quinalt’ (F. x ananassa) flowered only under long days. While those genotypes that flowered under both LD and SD can be considered day-neutral, they varied in the degree of floral response to the two photoperiods. CFRA 0368 and Frederick 9 produced the same number of flowers under both LDs and SDs, while ‘Aromas’ and ‘Tribute’ had more flowers under LDs and RH 30 had more under SDs. Of the DN genotypes, LH 50-4 and RH 30 were the only ones that produced runners under SDs. Flowering in ‘Fort Laramie’ was least affected of any genotype by high temperature, although its dry weight was negatively impacted. Based on these data, several genotypes show promise as breeding parents: CFRA 0368 and Frederick 9 to equalize flower production under LD and SD conditions, LH 50-4 and RH 30 to produce more freely runnering DNs, and ‘Fort Laramie’ for floral heat tolerance.     

Positive effect of salicylates on the flowering of African violet

Aqueous solutions of 1.0 μM to 0.1 nM concentrations of salicylic acid (SA) were sprayed on African violet grown under greenhouse conditions to estimate its effect on the flower expression of the plant. These solutions were sprayed on the shoots of the plant on three occasions, 21, 28 and 35 days after being potted. Salicyliclate at 0.1 nM increased the number of leaves from 16 to 19, the number of flower primordia from 8 to 14, the rosette diameter from 130 to 177 mm in comparison with the control. The same concentration induce flowering at 74 days of plant age whilest the control plants last 89 days to flower.     

The impact of photoperiod and irradiance on flowering of several herbaceous ornamentals

Forty-one herbaceous species were grown under short-days (8 h photoperiod, ambient irradiance averaged 12–13.2 and 6.4–8.3 mol m⁻² day⁻¹ for Experiments I and II, respectively) with or without supplemental high-pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹); or under long-days delivered using natural day lengths and irradiance with night interruption lighting (2200–0200 h at 2 μmol m⁻² s⁻¹ from incandescent lamps) or under ambient daylight plus supplemental irradiance during the day and as a day extension to 18 h (0800–0200 h) with supplemental high pressure sodium lighting (+50, 100, or 150 μmol m⁻² s⁻¹) to identify the impact of photoperiod and irradiance on flowering of each species. Days to first open flower, leaf number below first flower, and mean dry weight gain per day (MDWG) were measured when the first flower opened. Twenty-seven species were photoperiodic with examples of five photoperiodic response groups represented: obligate short-day (2), facultative short-day (5), obligate long-day (16), facultative long-day (4); 13 were day neutral (no photoperiod response in flowering). One species, Salvia sclarea L., did not flower. A facultative irradiance response was observed with 10 species; 28 species were irradiance indifferent; 2 had delayed flowering as irradiance increased. Photoperiod affected MDWG of 30 species. Increasing irradiance affected MDWG with 14 species. Photoperiod interacted with irradiance to affect MDWG of 11 species. Cobaea scandens had the greatest MDWG (0.40 g day⁻¹) while Amaranthus hybridus had the least MDWG (0.01 g day⁻¹) across photoperiod and irradiance levels.     

Investigation of plant growth and flower performance on a semi-extensive green roof

Understanding of plant growth and flower performance is crucial for appropriate planting design. This study was aimed to understand characteristics of growth pattern and flower performance in green roof plants and how plant species diversity effect these characteristics. A semi-extensive green roof was installed in 2005 and 54 species plant species were planted in 10 cm and 20 cm of the substrate in Rotherham, UK. Thirty-two quadrats (50 cm × 50 cm) were set up through the combinations of plant species diversity (high and low), planting density (high and low). Percentage of coverage and height of each species were recorded at every month from February to November 2006 in these 32 quadrates. Flowering time of each species was studied every two weeks from February to November 2006. Flowering time was various from plants; some showed a very long flowering time, over five months whereas some finished flowering within two weeks. The growth characteristics of individual plant species over time were categorized into six patterns of coverage and vertical growth pattern. Spread of individual plants was larger in high diversity of plants than those in low diversity of plants. Number of flowering was higher and overall flowering term was longer in the quadrats of higher plant species diversity than those of lower plant diversity. However, these tendencies were affected strongly by the combination of species used. Therefore, it is important to be aware of individual plant growth characteristics such as plant size, growth pattern and flower performance for planting design.     

The effects of NaCl pre-treatments on salt tolerance of melons grown under long-term salinity

The response of melon (Cucumis melo) plants to long-term salinity was investigated to determine the availability of the NaCl pre-treatments (seed priming + seedling conditioning) as an interesting strategy for increasing the salt tolerance. Seeds of melon cultivars “Hasanbey” and “Kirkagac” were primed with 18 dS m⁻¹ NaCl solution for 3 days at 20 °C. During emergence and seedling growth, non-primed seeds were irrigated with local irrigation water (EC: 0.3 dS m⁻¹) whereas primed groups were treated with 9.0 dS m⁻¹ saline solution for 35 days. Seedlings derived from pre-treated (P) and non-pre-treated (NP) groups were transplanted to 8 l pots. After transplanting, salinity treatments were started with the first irrigation. The salinity treatments consisted of five levels (control, 4.5, 9.0, 13.5 and 18.0 dS m⁻¹) of irrigation solution for a period of 90 days. NaCl pre-treatments diminished the inhibiting effect of salinity on growth of melon plants. However, competence for salt adaptation varied with cultivar and the level of salinity. The physiological response of the P plants was also maintained in the long-term. Stomatal conductance and relative chlorophyll content of P plants tended to be higher than those of the NP ones. In addition, NaCl pre-treatments enhanced K and Ca concentrations of leaves and stems, and prevented toxic effects of salinity because less Na accumulated in stems. These results suggest that the use of NaCl pre-treatments could be a useful strategy to increase the salt tolerance of melon plants in the long-term and also to permit the establishment of melon crop by direct sowing in a saline medium.     

Combining ability among male sterile two-type and restorer lines of Zinnia elegans and implications for the breeding of this ornamental species

Nineteen parental lines including five male sterile A-lines (AH002A, AH003A, AH209A, S5001A, J16A) and fourteen restorers (A1-GH, A3, S5, J6, J7N, J7J, J8, J9, J10, J11, J12, J13, J14, J17) were crossed using the North Carolina II statistical method. Studies of combining ability and heritability were conducted on selected parents along with their seventy F₁ hybrids for main ornamental traits. Plant height, crown size and length of node had obvious additive genetic effects, high (>0.50) broad sense heritability and high narrow sense heritability (length of node was medium). Pedicel length showed approximately equivalent maternal and paternal additive genetic effects, high broad sense heritability and medium (0.30–0.50) narrow sense heritability. Number of whorls of ray florets across capitulum and number of branches were able to take advantage of heterosis. The relationship between general combining ability and specific combining ability in Zinnia elegans depended on materials and traits. Male sterile two-type line was pivotal in the hybridization breeding of Z. elegans. S5001A, AH002A and A1-GH, A3, J14 which performed high negative GCA effects in PH, PL, LN and type I in PH, PL, NW, LN were ideal female and male parents of potted flowering plants; AH209A, J16A and S5, J10, J17 which displayed positive GCA effects and almost type I in PH, PL, LN were ideal female and male parents of cut flowers, respectively. For potted flowering plants, AH002A × J17, AH209A × A1-GH and S5001A × J6 with high negative SCA effects in PH, PL and LN were the most promising combinations, AH002A × S5, AH003A × A3 and J16A × J6 were the subprime combinations; for cut flowers, AH209A × S5, AH209A × J17 and J16A × J17 with high positive SCA effects in PH, PL and LN were the primary combinations, AH209A × J9 and S5001A × J10 were the secondary combinations.     

In vitro production of Prunus necrotic ringspot virus-free begonias through chemo- and thermotherapy

Prunus necrotic ringspot virus (PNRSV)-free Begonia spp. plants were raised from petioles of virus-infected plants using in vitro techniques. The petioles were grown on MS medium supplemented with 0.2 mg/l NAA and 0.2 mg/l BAP (pH 5.8). For rooting, half-strength MS medium without any plant growth regulators was used. On rooting medium, shoots were subjected to chemotherapy (virazole, 2-thiouracil or 6-azauracil) and thermotherapy (38 °C for 16 h light period and 22 °C for 8 h dark period) separately or in combination. Regenerated plants (treated with chemo- and thermotherapy) were indexed for PNRSV by DAS-ELISA and RT-PCR. An amplified product of 785 bp was obtained by RT-PCR in PNRSV-infected plants. Virazole at a concentration of 20 mg/l was found to be more effective (30 and 20% of PNRSV-free plants as indexed by ELISA and RT-PCR, respectively) in comparison to the other chemicals. Thermotherapy for 25 days gave 35 and 25% PNRSV-free plants as indexed by DAS-ELISA and RT-PCR, respectively. A combination of both treatments gave a good number of PNRSV-free plants (67.5 and 57.5% as indexed by DAS-ELISA and RT-PCR, respectively). At higher concentrations all three chemicals were found to be toxic. Thermotherapy for more than 25 days caused browning of leaves and shoots died.     

Shoot induction and plant regeneration from receptacle tissues of Lilium longiflorum

An efficient system has been developed for the in vitro plant regeneration of Lilium longiflorum Thunb. by culturing receptacle sections from flower buds. The sections were cultured on one-half MS medium plus 30 g l⁻¹ sucrose, 8 g l⁻¹ agar, 5.4 μM NAA or 4.9 μM IBA plus 2.2 μM BAP. A section size of 3–4 mm was found to be optimal. After 60 days an average of 41 shoots were formed per explant. More vigorous shoots were obtained by subculturing on hormone-free medium with 20 g l⁻¹ sucrose. Rooting occurred on one-half MS medium with 1.1 μM NAA. Rooted plants were hardened-off in a greenhouse for two months, and normal flowering plants were produced.     

Impact of branch reorientation on breaking stress in Liriodendron tulipifera L.

It has been observed that during ice, snow, and wind storms, branches oriented vertically tend to incur more damage than branches oriented horizontally. A study was conducted to determine breaking stress and breaking position of branches reoriented nearly horizontal and nearly vertical. Branches oriented 40–50° from horizontal with mean diameter 4.9 cm (SD ± 0.73) were removed from two trees and transferred to a custom branch pulling station. Branches were reoriented either nearly horizontal (76–89°) or vertical (6–29°) to a reinforced vertical post. Branches were pulled vertically downward from three equidistant positions along the branch until they broke. Failure stress for horizontal oriented branches (64 MPa) was double the stress required to pull vertical oriented branches to failure (32 MPa). Nine of ten horizontal branches failed between the branch base and the pull point closest to the base (proximal pull point); whereas seven of ten vertical branches failed farther from the base, between the proximal and middle pull points. Average length from branch base to failure point for horizontal branches was 12.8 cm, and 74.6 cm for vertical branches. Despite requiring less stress to break, branch angle change at the distal and middle pull points from the original position to the position at failure for vertical branches was greater than for horizontal branches; whereas angle change at the proximal pull point was greater for horizontal branches. Branch taper was not different between reorientation treatments. Implications on pruning strategies are discussed.     

Effect of photoperiod on flower bud initiation and development in myoga (Zingiber mioga Roscoe)

Selection of suitable production locations in Australia and New Zealand for production of myoga (Zingiber mioga Roscoe) has been limited by lack of information on climatic influences on flowering. This study focused on photoperiod as potential production sites within Australia differ considerably in daylength due to the geographical range. The two cultivars available in Australia (Inferior and Superior) were examined in this trial due to previously observed differences in vegetative and reproductive development.Plants grown under long-day conditions (16 h) and short-day conditions (8 h) with a night break produced flower buds, while those under short-day conditions (8 h) did not. The failure of plants under short-day conditions to produce flower buds was due to abortion of developing floral primordia rather than a failure to initiate inflorescences. It was concluded that for flower development in myoga a qualitative long-day requirement must be satisfied, but that flower initiation was day-neutral.Short-day conditions resulted in abortion of flower primordia, premature senescence of foliage and reduced foliage dry weight in both cultivars. Early senescence and low flower bud yield of the Inferior cultivar, but not the Superior cultivar have been observed in crop evaluation trials in Southern Australia and New Zealand. Differences in critical photoperiod between the two cultivars may explain this observation and therefore photoperiodic requirements may be an important consideration in site and planting date selection for different cultivars.     

Performance of geophytes on extensive green roofs in the United Kingdom

Dwarf geophytes have great potential for use on extensive green roofs because they often come from arid areas and can survive dry and hot summer in a dormant state. However, there has been little research regarding geophytes on green roofs. This experiment was conducted to study the performance of 26 species of geophytes on a green roof during 2005–2006 in Sheffield, UK. The geophytes were grown at two substrate depths (5 cm and 10 cm) of substrate on a green roof without irrigation. To investigate the susceptibility of geophytes to competition from a covering of permanent plants, the geophytes were grown with or without a surface vegetation layer of Sedum album. Overall, the growth, survival rate, regeneration and flowering of geophytes were more successful at a substrate depth of 10 cm than of 5 cm, probably because of improved moisture retention, fewer temperature fluctuations and the protection from digging by animals. The flowering period was limited to spring, therefore, it is recommended to combine with other plant species such as covering plants. Geophyte species did not compete much with S. album and Sedum cover had no significant effects on the growth, survival rate, regeneration and flowering of geophytes in most species. Iris bucharica, Muscari azureum, Tulipa clusiana var. chrysantha, Tulipa humilis, Tulipa tarda and Tulipa turkestanica had good performance at the substrate depth of 5 cm. In addition, Narcissus cyclamineus ‘February gold’ and Tulipa urumiensis exhibited a successful performance at the substrate depth of 10 cm.     

GA4+7 plus benzyladenine reduce foliar chlorosis of Lilium longiflorum

The effectiveness of two commercial formulations of gibberellin (GA) and benzyladenine (BA) for reducing foliar chlorosis on Easter lily (Lilium longiflorum Thunb.) was compared. On a per liter basis, plants were sprayed with 0, 100, 200, or 400 mg (BA equivalent) of Accel (GA₄₊₇:BA of 1:10) or Promalin (GA₄₊₇:BA of 1:1) when the crop leaf area index (LAI)=3. One group of plants was sprayed with 100 mg of Accel or Promalin (BA equivalent) per liter twice: once at LAI=3 and again 3 weeks later. Plants were harvested when the largest flower bud on each plant measured 13 cm in length, stored for 0 or 3 weeks at 2.5°C in the dark, and then moved into a post-harvest evaluation room at 21°C, where foliar chlorosis was monitored for 3 weeks. Senescence of some lower leaves on plants in every treatment was evident at harvest, and incidence of senescence increased during the 21 days of post-harvest evaluation. Cold storage increased the number of leaves senescing during the subsequent evaluation period. Application of Promalin or Accel significantly reduced leaf senescence compared to that of untreated plants. At harvest, 21% of the leaves on untreated plants were senescent, while plants treated with Promalin or Accel averaged 3 or 9% senescent leaves, respectively. Following 7 days of post-harvest evaluation, Promalin was more effective in preventing chlorosis than Accel at the 400 mg l⁻¹ (BA equivalent) level. Following 14 or 21 days of post-harvest evaluation, Promalin was more effective than Accel for the 100 mg l⁻¹ 2× and 400 mg l⁻¹ (BA equivalent) treatments.Plants in all Promalin and Accel treatments were taller than untreated plants 1 week after sprays were applied. At harvest, plants sprayed with Promalin were between 6 and 14 cm taller than untreated plants, but those treated with Accel were the same height as untreated plants.Neither Promalin nor Accel influenced the occurrence of malformed or aborted flowers in this study. However, cold storage significantly increased the number of plants with aborted buds and malformed flowers. Unstored plants averaged 0.16 aborted buds and 0.02 malformed flowers each, while those stored 3 weeks averaged 0.51 aborted buds and 0.18 malformed flowers each.     

Arsenic as a factor affecting virus infection in tomato plants: changes in plant growth,peroxidase activity and chloroplast pigments

The influence of arsenic and Cucumber mosaic virus (CMV), applied separately and simultaneously on young tomato plants was studied. The plants were cultivated in containers under glasshouse conditions. Four main variants were arranged. The first one was without additional As pollution of soil, named as a control, and the other three variants, with As added at 25, 50 and 100 mg kg⁻¹ to dry soil respectively. Half of the plants in each experimental container were inoculated with CMV and the rest uninoculated. A clear response in plant behavior under the conditions of biotic and abiotic stress was estimated. Both arsenic and virus infection had a negative effect on tomato plants by limiting the growth of their roots and above growth parts. The changes in roots were more significant than of stems. Virus infection was a stronger stress factor than arsenic applied at levels of 25 and 50 mg kg⁻¹. The effect of each stress factor applied separately was enhanced in cases of their simultaneous application. The strongest negative effect was manifested in the infected plants, treated with excess arsenic of 100 mg kg⁻¹. It was established that the infection, caused by CMV in tomatoes, was affected by the presence of arsenic in the soil and concentration of the latter. Doses of 25 and 50 mg kg⁻¹ were favorable for infection development, while the dose of 100 mg kg⁻¹ was an inhibitor.Virus infection induced stronger specific peroxidase activity (SPOA) than As treatment. The combination of both stress factors reduced the positive peroxidase response caused by virus infection. Arsenic at rate 50 and 100 mg kg⁻¹, virus infection and the combination of both stress factors at 25 mg kg⁻¹ reduced chlorophyll a, chlorophyll b and carotenoid content The virus infection in cases of the higher arsenic doses reduced the As effect. There was an interaction between the two effects of biotic and abiotic stress. When arsenic and virus infection were applied simultaneously, they caused modification of the effect of each stress on the plants, when applied separately.     

Temperature effects on corm dormancy and growth of Zephyra elegans D.Don

Experiments were performed with the Chilean geophyte Zephyra elegans, a potential cut flower, to evaluate the effect of corm weight and storage temperature on corm dormancy, and to determine the effect of day and night growing temperatures on its growth and flowering. Z. elegans has a deciduous and synanthous growth habit and the corm is replaced annually. Dormant corms were stored at different constant temperatures or temperature combinations from 20 to 40 °C. Corms released from their dormancy were grown at 15/10, 20/15, or 25/20 °C day/night temperatures. Corms of various weights were planted at the same date after being stored dry at 25 °C for 22 weeks. They all emerged 19–38 days after planting, showing that dormancy release was not affected by corm weight. A 20-week corm storage treatment at a constant 25 °C resulted in the most rapid corm sprouting. Sprouting percentage was reduced at higher or lower storage temperatures. Temperature also affected plant growth. When plants were grown at 15/10 or 20/15 °C they emerged and flowered more rapidly than when they were grown at 25/20 °C. The latter growing temperature also resulted in poor flower quality.     

Daylength and photon flux density influence the growth regulator effects on morphogenesis in epicotyl segments of Troyer citrange

The optimal growth regulator addenda for adventitious shoot regeneration in epicotyl cuttings of Troyer citrange (Citrus sinensis×Poncirus trifoliata) varied with the conditions of illumination. The response to illumination and to growth regulators differed for the direct and the indirect (through callusing) pathways of regeneration. Shoot formation through the direct organogenic pathway decreased as the concentration of benzyladenine (BA) in the medium was increased in the range 2.2–22 μM, when the explants were incubated in the dark or under an 8 h daylength. For explants incubated under a 16 h daylength, the number of shoots formed increased with BA concentration. Optimal conditions of incubation for shoot formation through the direct pathway were either an 8 h daylength with a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA, or a 16 h daylength with a photon flux density of 37 μmol m⁻² s⁻¹ in the presence of 22 μM BA. Irrespective of the conditions of incubation, shoot formation through the indirect organogenic pathway was suppressed by the addition of 22 μM BA to the medium. Optimal conditions for shoot formation through this pathway were incubation under an 8 h daylength at a photon flux density of 74 μmol m⁻² s⁻¹ in the presence of 2.2 μM BA. At the optimal conditions indicated, the addition of the synthetic auxin naphtaleneacetic acid (0.54 μM) reduced shoot formation. Irrespective of the pathway of regeneration, the number of shoots formed decreased markedly with the distance of the cutting from the cotyledonary node.     

Cold treatment modifies the photoperiodic flowering response of Lobelia×speciosa

Lobelia×speciosa Sweet ‘Compliment Scarlet' was grown under a range of photoperiods and low temperature treatments to determine their effects on flowering. In the first experiment, plants were held at 5°C for 0 or 15 weeks, then grown at 20°C under the following photoperiods: 10, 12, 14, 16, or 24 h of continual light or 9 h with a 4 h night interruption (NI). Non-cooled ‘Compliment Scarlet' flowered as a qualitative long-day plant (LDP) with a minimum flowering photoperiod of 14 h. Following cold, flowering was quantitative with respect to photoperiod, until ≈14.2 h, when the calculated rate of progress toward flowering reached a plateau. In cooled plants, node number below the inflorescence decreased from 27 to 16 as the photoperiod increased from 10 to 24 h. Cooled plants developed 61–149% more flowers and were ≥17% taller than non-cooled ones under the same photoperiod. To determine the cold duration required for flowering under short days (SD), plants were held at 0, 3, 6, 9, 12, or 15 weeks at 5°C then grown at 20°C under SD (9 h photoperiod) or long days (9 h photoperiod with a 4 h NI). Under SD, few plants flowered after ≤6 weeks of cold. As cold treatment increased from 9 to 15 weeks, flowering percentage increased, time to flower decreased from 93 to 64 days, and node count decreased from 24 to 13. Cold treatment did not affect flowering percentage or time under NI, but plants always had more flowers and were taller than reproductive ones under 9 h day lengths. Thus, ‘Compliment Scarlet', is a qualitative LDP, but an extended cold treatment can partially substitute for the long day (LD) photoperiodic requirement.     

珠三角地区稻后冬闲田直播油菜薹品质分析

为分析珠三角地区冬种油菜的菜薹采摘效益，以油菜“希望669”为材料，在广东江门新会区采用直播方式播种，分析比较不同播期（稻收后15 d和稻收前3 d）下油菜薹宜采期的品质差异。结果表明：不同播期下油菜不同生育时期品质存在显著性差异，均略优于菜心。其中，在油菜初花期之前（春节期间）的宜采期，油菜薹单位面积生物量与油菜薹维生素C、可溶性蛋白含量及叶片SPAD值均表现出稻收前播种优于稻收后，而纤维素含量则相反。在油菜初花期后，油菜薹可溶性糖含量表现为稻收前播种优于稻收后。2个播期下冬种油菜的菜用可采期均与珠三角蔬菜市场短缺期重合；因此，冬种油菜可以调节春节市场油菜薹的有效供给，产生良好的社会和经济效益。