The response of partly cooled tulips to vacuum infiltration with gibberellins

Partly cooled (5°C) tulip ‘Apeldoorn’ were treated with gibberellins GA₃ and GA_{4 + 7} by vacuùm infiltration, with a view to defining conditions suitable for exploiting the effects of GA on forced tulips (faster flowering, control of stem extension, reduction of floral bud blasting).The first experiment showed that GA₃ and GA_{4 + 7} were equally effective in reducing the glasshouse period following 6 or more weeks cold storage; with less than 6 weeks cold storage, effects were less marked. Stem length at flowering was reduced by GA treatments, particularly by GA₃ and following more than 6 weeks cold storage. However, the vacuum infiltration method used (30 min at 10 torr) resulted in serious flower losses.Next, the effect of GA₃ concentration (up to 1500 mg 1^?1) was studied using vacuum infiltration treatments for 1–15 min at 20–510 torr, which resulted in fewer flower losses. Following 4 weeks cold storage, reducing pressure or increasing GA₃ concentration reduced both glasshouse period and stem length, with no effect of duration of treatment; GA₃ concentration was the only factor affecting flower length, which was increased. Following 8 weeks cold storage, increasing GA₃ concentration, vacuum or duration reduced glasshouse period. With all 3 factors at their maximum levels, 16 days earliness was obtained compared with controls. With maximum earliness, stem length was reduced to about 23 cm, compared to about 26 cm for treatments giving about 1 week's earliness, and 32 cm for untreated controls. Increasing vacuum appeared the most economical way of obtaining earliness, 20 torr giving 7 days earliness even at only 250 mg GA₃ 1^?1. Treatments giving earlier flowering also gave larger flowers. For comparison, there was little effect of soaking bulbs at atmospheric pressure even at 500 mg GA₃ 1^?1 for up to 20 h.Further experiments, conducted with vacuum infiltration at 260 torr for 15 min, confirmed these GA effects using formulated GA₃ (as “Berelex”) and GA_{4 + 7} (as “Regulex”). Effects of GA on stem length at flowering had disappeared by the time stems reached their final length. Comparisons with bulb injection of GA showed that this method required less GA than vacuum infiltration for similar effects, and that the greater effectiveness of GA_{4 + 7} compared with GA₃ was less marked using vacuum infiltration.     

Early forcing of narcissus: The effects of lifting date and stage of floral development at the start of cooling

Early Narcissus flowers may be obtained if bulbs are lifted early from the field, warm-stored (35°C) and then cool-stored (9°C) before forcing in a glasshouse. The earliest satisfactory forcing was investigated, in ‘Carlton’ and ‘Fortune’, by lifting weekly from 27 May to 22 June, and storing at 17°C for 0–7 weeks between warm- and cool-storage. Storage at 17°C is usually intercalated to allow the completion of flower differentiation prior to the start of cool storage.After warm-storage, the bulbs lifted on 27 May and 22 June had reached Stages Sp and A2 of flower differentiation, respectively; 5–7 weeks of 17°C-storage were then needed to reach complete flower differentiation (Stage Pc). Cool storage was therefore begun with bulbs ranging from Stage Sp to Stage Pc. The earliest cooled bulbs had progressed only to Stage A2, and all others to Stage Pc, after 14–16 weeks of cool storage. No floral defects (e.g., split paracorolla) were noted in any treatment, but in ‘Carlton’, about half the bulbs lifted on 27 May and stored for 0 or 1 week at 17°C did not yield a flower, due to failure of the scape to elongate and death of the flower bud within the spathe.Duration of the glasshouse period was reduced by later lifting and by longer 17°C-storage, but following lifting on 15 or 22 June and 2 or more weeks at 17°C, differences were trivial. For flowering within 30 days in the glasshouse, 5 or 6 weeks' 17°C-storage was needed with 27 May lifting, reducing to 1 week at 17°C after 22 June lifting. Flowering within 21 glasshouse days was achieved only after 15 or 22 June lifts followed by 4–5 weeks at 17°C. The earliest flowers in ‘Fortune’ (7 November) were produced following 3–5 weeks at 17°C after lifting on 27 May or 1 June, or following 1–2 weeks at 17°C after later lifting. In ‘Carlton’, the earliest flowers (23 November) followed 2–3 weeks at 17°C after lifting between 1 and 15 June, or 0–1 weeks at 17°C after the last lifting date (22 June). Following the use of 3 weeks' 17°C-storage, flowering date was about equal, irrespective of lifting date. However, further extension of 17°C-storage resulted in a delay in flowering date. Scape length increased irregularly with longer storage at 17°C; scapes were taller following later lifting (8–22 June) than following earlier lifting. Differences in flower diameter between treatments were relatively small.     

Gibberellic acid soak treatments for fully-cooled tulips

In attempts to reduce the glasshouse period of fully-cooled 5°C-forced tulips, ‘Apeldoorn’ bulbs were soaked before planting in aerated and non-aerated gibberellic acid (GA₃) solutions for 2–48 h. A 48-h treatment with 250–500 mg l^?1 GA₃ was the most effective, giving a glasshouse period 7–11 days shorter than for untreated bulbs. Soaks for 24 and 48 h caused root emergence, and 48-h soaks caused perianth segment splitting in one experiment. Aerated or non-aerated GA₃ solutions gave similar results. Soaking in water alone gave a smaller increase in earliness. In general, a shortened glasshouse period was associated with shorter whole stem and last internode lengths. In GA₃ treatments, flower losses were lower than for distilled water treated and untreated bulbs. A practical treatment would be a non-aerated soak for 24 h with between 250 and 500 mg l^?1 GA₃.     

Effect of exogenous growth regulators on flowering and cytokinin levels in azaleas

‘Alaska’ and ‘Redwing’ azaleas having dormant flower buds were sprayed with gibberellins (GA₃ or GA_{4 + 7}) alone and in combination with thiourea, N⁶ benzyl adenine (BA) or kinetin weekly for 3 or 4 weeks to test the efficacy of these materials in breaking bud dormancy. Additional plants received 6 weeks of cold storage at 4.5°C or glasshouse day temperatures of 21°C and above. The 2000 and 3000 mg l^?1 GA₃ and Ga_{4 + 7} sprays were better than 1000 mg l^?1 in promoting flowering, with ‘Redwing’ responding better than ‘Alaska’. GA-treated plants flowered in fewer days than those receiving cold storage. Flower diameter and pedicel length increased with higher levels of GA, and flower uniformity was comparable to cold-stored plants on most GA-treated ‘Redwing’-plants. Thiourea, BA and kinetin applied alone had no effect and considerable cytokinin activity was highest in GA-treated buds 14–21 days after treatment application. No increase in activity occurred on plants not receiving GA.     

Effects of cold storage on postharvest leaf and flower quality of potted Oriental-, Asiatic- and LA-hybrid lily cultivars

The effects of cold storage of mature potted plants on postharvest leaf and flower quality were investigated in several cultivars of three major groups (Oriental, Asiatic and LA) of hybrid lilies (Lilium spp.). Mature plants were stored in darkness at 3 °C for 2 weeks before placing them in a postharvest evaluation room (22 °C) and were compared with plants moved directly to the evaluation room. The efficacy of GA₄₊₇ plus benzyladenine (BA) treatments (applied just before cold storage) for preventing cold-induced postharvest disorders in each cultivar was also evaluated. In all cultivars, cold storage caused several adverse effects on postharvest quality, including accelerated leaf yellowing or browning, bud abortion and reduced flower or inflorescence longevity. Leaf abscission was observed only in Oriental-hybrids. Treatment with GA₄₊₇ plus BA significantly reduced these disorders and improved the overall postharvest quality after cold storage. While different cultivars differed greatly in their sensitivity to cold storage, all the cultivars benefited from GA₄₊₇ plus BA treatment. Experiments indicated that GA₄₊₇ plus BA treatments could be applied as early as 2 weeks before the mature bud stage without compromising the positive effects.     

Substitution of the cold requirement of tulip CV. ‘apeldoorn’ by GA3

To investigate whether GA₃ can substitute for the requirement, 1 mg GA₃ was injected in dry stored bulbs before, during or after the following treatments: (a) 12 weeks at 21°C, (b) 12 weeks at 5°C, (c) 6 weeks at 21°C followed by 6 weeks at 5°C, and (d) 6 weeks at 5°C followed by 6 weeks at 21°C. The bulbs were then planted in light at 15°C. Plants from bulbs previously subjected to (d) flowered earlier than bulbs from treatments (a) and (c) but later than those subjected to (b). Both the GA₃ and the 5°C treatments shortened the time from planting until flowering; however, GA₃ produced shorter plants and induced the formation of parthenocarpic fruits. Reduction of scape length by GA₃ was less when it was given at a later time during treatments (a) and (c) whereas the scape lengths of bulbs subjected to treatments (b) and (d) were hardly affected by the time chosen for GA₃ application.     

High-Temperature Treatment (Blindstoken) of Bulbs of Tulip cv Rose Copland for Flower Killing and Yield Improvement

A three-year experiment on the high-temperature treatment of tulip bulbs established that yield could be increased by between 8 and 31 % for bulb weight or between 14 and 29 % for numbers of large bulbs, depending upon season, associated with a near-complete flower kill. The optimum pre-treatment storage temperature was 17°C, and the best date (of the five tested) for starting blindstoken at 33°C for one week was 20th-21st September.

Yield increases were greater when the blindstoken treatment was applied to bulbs whose shoots were short; later treatment, or treatment after pre-treatments which allowed faster shoot growth, were less effective. For optimum flower kill and yield increase the shoot should be about 1 cm high at treatment. Bulb weight and large bulb number were correlated, suggesting that the treatment increases total bulb weight by increasing bulb size rather than by differentially affecting the growth of daughter bulbs.

No adverse effects of the treatments were observed when the bulbs were forced in a glasshouse the following season.     

Cold treatments enhance responsiveness to gibberellin in stock (Matthiola incana (L.) R. Br.)

Summary

Endogenous GAs have been suggested as regulators of stem elongation and flowering of cold-requiring plants. Here, the relationship between temperature conditions and responsiveness to GA₄ on stem elongation and flowering of stock (Matthiola incana) was investigated. The optimum temperature for induction of flower bud initiation was 10°C, and the minimum duration was 20 d in the late flowering cv. Banrei; the type of cold treatment effect on flowering was classified as a “direct effect”. Stem elongation was markedly promoted by cold treatment regardless of flower bud initiation. The cold treatment amplified the stem elongation response to GA₄. The GA₄ level necessary for flower bud initiation was lower in the 10°C treatment than in the 15°C treatment, and it became lower at longer durations of cold treatment. These results indicate that the cold treatments enhance responsiveness to GA₄ not only in the stem elongation process but also in the flower bud initiation process and that the development of responsiveness to GA₄ may correlate with the temperature and duration of cold treatment.     

Hormonal control of shoot elongation in tulips

Shoot elongation of both cooled and uncooled ‘Apeldoorn’ and ‘Oxford’ tulips, as regulated by the leaves and the flower-bud, was studied. Leaves and/or flower-buds were excised and IAA, BA, or GA₃ in lanolin paste, was applied at various sites.Excision of the leaves and flower-buds of cooled tulips inhibited the elongation of the stem internodes. Administration of auxin after leaf and flower excision restored the elongation, mainly basipetally from the site of application. The findings may indicate that both the leaves and the floral organs provide auxin-like substances which control the elongation growth of the stem.Stems of uncooled tulips also elongated after IAA administration to the stem, but the response was slower and weaker. One part of the effect of cooling might be the stimulation of an auxin-releasing activity in the leaves and the flowers, another part an effect on the auxin-response system.     

The cold requirement of tulip cultivars

Results of 8 years of trials have been used to assess the cold requirements of 116 tulip cultivars, expressed as the number of days of cold (9°C) required to produce flowers in 21 days at 18°C. The data are compared with commercial recommendations for the dates of transferring tulips to the glasshouse for forcing.     

Effects of chilling on the formation of secondary growing-centres in flowers of the glasshouse carnation

The incidence of secondary growing-centres within the flowers of carnation was increased when plants were chilled at 5°C for 1–3 weeks during flower development. Application of GA₃ to shoots in the early stages of flower formation also caused an increase in the number of secondary growing-centres formed. Shoot tips excised from plants that had been chilled yielded greater amounts of diffusible gibberellin-like substances than shoot tips excised from plants that had been grown at normal glasshouse temperatures. It is suggested that endogenous gibberellins have a role in controlling the formation of secondary growing-centres within the flower.     

The effect of gibberellic acid on sprouting and flowering of some tulip cultivars

The effect of gibberellic acid, GA₃, on breaking of dormancy, sprouting and flowering of 9 cultivars of tulips was investigated, using 4 cultivars recommended for forcing and 5 not suitable for forcing. GA₃ was applied to the basal plates of the bulbs in a lanolin paste before planting, or was injected into the bulbs prior to rooting or after 38 or 64 days of cold treatment. The application of GA₃ stimulated sprouting, growth of floral stalks and flowering in all investigated cultivars. Injection of GA₃ was more effective than topical application. The effect of GA₃ on sprouting and flowering of plants was especially effective after 38 or 64 days of cold treatment. The possibility of applying GA₃ in commercial horticulture is considered.     

The Effect of Cold Storage and Treatment with Gibberellic Acid on Flowering and Bulb Yields of Dutch Iris

Iris bulbs of the varieties Wedgewood and Prof. Blaauvv were injected with 50 or 500 μg. gibberellic acid (GA) before or after cold storage (10° C.) of 18 or 35 days. GA injection accelerated flowering by up to 19 days ; it had little or no effect on length of leaves or flower stem. It was most effective when applied at an early stage after flower initiation.

GA injection reduced bulb yield of Wedgiwood plants, and had no effect on, nor increased bulb yield of, Prof. Blaauw plants.

GA spraying (seven times at 10^-2M of GA) accelerated flowering and increased foliage growth in both varieties. It increased flower stem elongation and reduced bulb yield in Wedgfcwood plants.     

Effects of Gibberellic Acid and Temperature on the Growth of Young Seedlings of Syringa Vulgaris L.

The application of gibberellic acid (0, 5, 20 and 80 µg) to seedlings of Syringa vulgaris L. about two weeks after germination increased significantly the total length, the length of internodes and the dry weight (d.w.) of shoots and the net assimilation rate. GA₃ also had a small but significant positive effect on the number of pairs of leaves, especially at high temperatures; it increased the girth, but this effect was not significant.

GA₃ reduced significantly the d.w. of roots and leaves but did not affect the leaf/root ratio. GA₃ had no effect on the total plant d.w. or the relative growth rate.

The effect of GA₃ on shoot growth was dependent on temperature and on the stage of growth. One and two weeks after its application it had the maximum relative effect at high temperatures (21–24 °C) but at the end of the experiment (8.5 weeks) the maximum effect was reached at 12 °C; it decreased with increasing temperature and was not significant at 24 °C. By this stage there were, however, no statistical interactions between temperature and GA₃ for total length and for d.w. of shoots, roots, leaves and of the whole plant.

Increasing temperatures over the range 12–24 °C resulted in increases in the following characteristics: the number of pairs of leaves; length of internodes, diameter and total length of the shoot; the d.w. of shoots, roots, leaves and of the whole plant; the d.w. ratios of leaves/roots and shoots/roots; and the relative growth rate and net assimilation rate. High temperatures reduced the root/whole plant dry weight ratio. The effect of temperature on the number of pairs of leaves was linear, and results at alternating temperatures (24°/18° and 21°/15 °C, 8 hr/16 hr) did not deviate significantly from values expected on the basis of mean daily temperature.     

Effects of Environment on Flower Initiation in Carnation

The main object of the investigation was to attempt the separation of effects of photoperiod and total incident light energy in controlling flower initiation in the glasshouse carnation, variety White Sim.

Low light intensities delayed flower initiation. The delay was associated with reduced rates of growth in terms of dry weight, reduced rates of leaf initiation and increased number of leaves formed below the flower. Short days also delayed flower initiation and increased the number of leaves formed below the flower. Photoperiod, however, had no appreciable effect on growth in terms of dry weight or on rates of leaf initiation, but internode length was greater in long days than in short days. A period of illumination given in the middle of the night was more effective in promoting flower initiation than an equivalent period given to extend the day. Internode length was similar in these treatments. Effects of night temperature were less consistent than those of light intensity or daylength but, under most of the conditions tested, high night temperatures (minimum 65° F. (18° C.)) delayed flower initiation and increased the number of leaves formed below the flower. Low temperature treatment of plants at 40° F. (4.5° C.) for one month promoted subsequent flower initiation and reduced the number of leaves formed below the flower.     

Effect of stratification-temperature,chemical treatments and seed coat on the growth of peach seedlings cultivar ‘Sharbati’

In order to obtain normal seedlings of peach cultivar ‘Sharbati’ before the commencement of winter, treatments with GA₃, thiourea and kinetin were given to seeds before stratification at 7°C, 10°C or 24°C. The seedlings raised from the treated seeds and after-ripened at 24°C were dwarf. The seedling growth was increased when the treated seeds were stratified at 10°C or 7°C and the stratification period was prolonged from 15 days to 75 days. 10°C stratification-temperature was better than 7°C. The seedling growth was improved when the seed coat was removed before the treatments. With respect to both seed types, 1000 mg/l GA₃ produced the tallest seedlings at all the after-ripening temperatures and during each stratification period. The next best treatment was 100 mg/l kinetin.     

The influence of preplanting dips and postplanting temperatures on root growth and development of nonprecooled tulips,daffodils and hyacinths

The effects of preplanting dips and postplanting temperatures were studied, using nonprecooled bulbs of Tulipa gesneriana L. ‘Paul Richter’, Narcissus pseudonarcissus L. ‘Explorer’ and Hyacinthus orientalis L. ‘Pink Pearl’, for 2 consecutive years. Preplanting treatments consisted of a non-dip control, and 30-min dips of either tap water or benomyl—ethazol. After planting, the tulips and daffodils received temperatures of 5, 9, 13, 17 or 21° C for a 5-week period. Hyacinths received temperatures of 9, 13, 17, 21, 25, 29 or 33° C for 5 weeks in the first year and for 25 days in the second year.It was determined that 17° C for 3 weeks and 17° C for 3–4 weeks were the optimal temperatures and periods of time for root development of tulips and daffodils, respectively. For hyacinths, a range of from 17 to 25° C for 10–14 days was optimal. Under these conditions, a minimum root length of 70 mm was obtained and all bulbs of each species had rooted.The benomyl-ethazol and water preplanting dips stimulated root growth for the first 2 weeks for tulips. This effect was not observed for daffodils and hyacinths.     

Gibberellin-like stimulation of celery (Apium graveolens L.) seed germination by N-substituted phthalimides

Thermodormancy of celery seeds incubated in the dark at 22°C was alleviated by two N-substituted phthalimides to the same extent as that normally achieved with a mixture of the gibberellins A₄ and A₇. As previously demonstrated with GA₄₊₇, the highly dormant cultivar ‘Lathom Blanching’ responded more to phthalimides in the presence of cytokinin, whereas ‘Florida 683’ required no cytokinin to elicit the maximum response to phthalimide treatment. Seed-soak treatments with either N-substituted phthalimide improved both the rate of germination and the percentage seedling emergence of both cultivars sown in compost under glasshouse conditions.     

The response of bud break and flowering to cool winter temperatures in kiwifruit (Actinidia deliciosa)

Summary

A range of temperatures (7°C, 10°C or 13°C mean) were imposed under controlled conditions on four year old, container-grown ‘Hayward’ kiwifruit vines. The treatments were applied for periods of from one to four months during the dormant period from May to September (Southern Hemisphere). Following these treatments the vines were held at a “forcing” temperature of 16°C mean until flowering. The objective was to define the response of bud break and flowering in spring to temperatures experienced during the preceding winter. Cool winter temperatures dramatically increased flower numbers, increased the proportion of bud break, advanced the day of bud break, and increased the duration from bud break to flowering. These responses were much larger between 13°C and 10°C than they were between 10°C and 7°C. For any treatment duration, the temperature imposed during dormancy had no effect on the time of flowering. Two months at cool temperatures produced the greatest number of flowers per winter bud, with reduced numbers at three and four months. The proportion of winter buds that produced shoots showed a similar response. The Richardson chill unit is frequently used to describe the effects of winter chilling on kiwifruit. It proved unreliable as an index to integrate the effects of temperature and time on any of the developmental variables monitored in this experiment.     

The Effects of Temperature,Extent of Evaporation,and Restriction of Ventilation on the Storage Life of Tomatoes

The storage life of English glasshouse tomatoes is generally terminated by the onset of rotting which at temperatures above 50° F. (10° C.) generally starts from the calyx. As the temperature of storage is reduced below 50° F. the skins of tomatoes become increasingly susceptible to fungal invasion.

Storage at 59° F. (15° C.), under conditions of restricted ventilation in controlled-atmosphere storage which allow exposure to more than 5% CO₂, , also renders the skins of tomatoes susceptible to fungal infection.

The establishment of infection is also greatly influenced by the extent of evaporation, i.e. by the humidity of the storage atmosphere.

The conditions for the storage of tomatoes and the precautions to be observed in prepackaging are discussed in the light of these effects.