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.     

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.     

The physiology of hyacinth bulbs. XI. The effect of gibberellic acid on the growth and flowering of variously chilled bulbs

The effect of gibberellic acid, GA₃, on the growth and flowering of hyacinth cultivars ‘Pink Pearl’, ‘Delft Blue’ and ‘Carnegie’, chilled in a cold room at 5°C or a garden frame for 28, 42 or 81 days, and either rooted or dry, unrooted, was investigated. GA, was applied to the basal plates of the bulbs in a lanolin paste on 10 October 1975.The growth of the inflorescence and leaves of plants originating from dry-chilled bulbs was generally the same as that of those grown from rooted plants. A similar response to GA₃ treatment was observed in all cultivars. Treatment of bulbs with GA₃ decreased the number of days to flowering, stimulated the growth of inflorescences and leaves, and its effect was most pronounced in the plants chilled for shorter periods.     

The physiology of hyacinth bulbs. XV. The effect of gibberellic acid and silver nitrate on dormancy release and growth

The effect of gibberellic acid (GA₃), supplied to dormant hyacinth bulbs of cultivars ‘Lady Derby’ and ‘L'Innocence’ by vacuum infiltration, on growth and flowering was investigated. Results showed that GA₃ in all applied concentrations (50, 500, 1000 and 5000 mg/l) accelerated growth and flowering in both cultivars, after chilling for 42 days in a garden frame in natural conditions or chilled dry in cold storage at 5°C. Bulb infiltration with 10 mg/l AgNO₃ resulted in the acceleration of flowering only in ‘L'Innocence’, but stimulated the growth of the inflorescence stalk and leaves in both cultivars regardless of the mode of chilling.The infiltration method was confirmed to be very promising.     

Long-day control of flowering in everbearing strawberries

Summary

Photoperiod and temperature control of flowering in a number of perpetual-flowering or everbearing strawberry cultivars of widely varying pedigree has been studied in controlled environments. Flower bud initiation in the cultivars ‘Flamenco’, ‘Ridder’, ‘Rita’ and ‘Rondo’ was significantly advanced by long-day (LD) conditions at temperatures of 15°C and 21ºC; while, at 27ºC, flowering took place under LD conditions only. Some plants of the seed-propagated F₁-hybrid ‘Elan’, raised at 21°C, also flowered under short-day (SD) conditions at 27°C, but reverted to the vegetative state after a few weeks when maintained under these conditions. When vegetative plants growing in SD at 27°C were transferred to LD conditions at the same temperature, they consistently initiated flower buds and started flowering after about 4 weeks. At such a high temperature, flowering could thus be turned on and off by switching between SD and LD conditions. This applied to all the cultivars studied. Also the cultivar ‘Everest’, which was tested only at 21°C, produced similar results. Night interruption for 2 h was effective in bringing about the LD response. At 9°C, flowering was substantially delayed, especially in ‘Flamenco’ and, at this temperature, flowering was unaffected by photoperiod. Runner formation was generally promoted by high temperature and SD conditions, but the photoperiodic effect varied between experiments. We conclude that everbearing strawberry cultivars, in general, whether of the older European-type or the modern Californian-type originating from crosses with selections of Fragaria virginiana ssp. glauca, are qualitative (obligatory) LD plants at high temperature (27°C), and quantitative LD plants at intermediate temperatures. Only at temperatures below 10°C are these cultivars day-neutral.     

Responses of Alstroemeria ‘Regina’ to temperature treatments prior to flower-inducing temperatures

Days to flower (DTF) were inversely related to the number of weeks (0–8) that Alstroemeria ‘Regina’ plants remained at 5°C, a vernalizing temperature, before being moved to 13°C, a vernalizing as well as a forcing temperature. However, when the number of weeks at 5°C was added to the DTF, no difference in the total time to flower was observed between plants treated at 5°C or those grown continuously at 13°C, as they both induced flowering. One-year-old plants maintained at 21°C, a non-inductive temperature, and not divided prior to the 5°C treatments, showed an increase in total shoot production, and delayed DTF, compared to plants which were divided. When divided plants were maintained for 16 weeks at 21°C prior to 5°C treatments, total shoot production was reduced but flowering was accelerated compared to plants maintained for 8 weeks at 21°C after dividing. Total shoot and flowering-shoot production was not affected by increasing the durations of time at 5°C when plants were grown at 21°C and divided prior to this treatment. Thus, the pre-treatment of dividing or maintaining plants at 21°C prior to a 5°C treatment affected subsequent shoot production and DTF.     

Effect of temperature on flowering in Primula vulgaris

When grown in a glasshouse, flowering in Primula vulgaris ‘Aalsmeer Giant’ (yellow) and ‘Ducat’ (blue) was delayed with increasing temperature from approximately 12°C to 18°C. In addition, size of the first open flower and the number of flowering axillary shoots decreased, whereas the number of leaves and leaf area increased with the temperature increase. All temperature responses were greater in ‘Aalsmeer’ than in ‘Ducat’.When grown in growth rooms at 9°C, flowering in P. vulgaris ‘Aalsmeer Giant’ (yellow) was inhibited compared with 15°C. However, when 9 weeks of 15°C was applied to plants grown for 9 weeks at 9°C, the inhibition was overcome; longer periods of 15°C being no more effective. This indicates than an early stage of flower formation, probably the initiation, in Primula vulgaris is inhibited by 9°C, and not the further development of the buds towards open flowers.     

Effect of day and night temperatures during short photoperiods on growth and flowering of Chrysanthemum morifolium Ramat

The effect of day and night temperatures of 10, 14 and 18°C on growth and flowering under short days was studied with six cultivais of chrysanthemum. A high day temperature resulted in earlier flowering and taller stems, but did not influence flower number and final total fresh weight, and only slightly influenced the distribution of fresh matter over stem, leaves and flowers. A high night temperature resulted in earlier flowering, more flowers and reduced stem and leaf weight. It did not affect leaf number and it influenced height and total fresh weight only slightly. Except for height, the day temperature acted independently from the night temperature. The cultivars responded similarly, except for two cultivars which generally did not flower at 10/10,10/14 and 14/10°C D/N. One cul-tivar produced more flowers at 14 than at 18°C.     

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.     

Increases in ethylene and carbon dioxide production by Tulipa gesneriana L. ‘Prominence’ after completion of the cold-requirement

Bulbs of Tulipa gesneriana L. ‘Prominence’ were either specially pre-cooled at 5 ± 0.5°C or held at 17 ± 0.5°C in a flow-through system equipped for atmospheric sampling. Bulbs at 17°C had low CO₂ and C₂H₄ production rates until January when they began to increase. An initial peak of C₂H₄ production occurred during the 2nd week of pre-cooling, followed by a major increase after 12 weeks. In addition, bulbs were specially pre-cooled for periods of 2–16 weeks (2-week increments). The bulbs were then transferred to 17 ± 0.5°C, where initial periods of special pre-cooling of greater than 12 weeks resulted in a dramatic increase in respiration rate over bulbs cooled for less than 12 weeks. These increases in C₂H₄ and CO₂ liberation appeared to be related to completion of the bulb cold-requirement. However, no surge of shoot elongation occurred after 12 weeks of pre-cooling and transfer to 17°C.     

Interaction of photoperiod and temperature in flowering-control of Gypsophila paniculata L

Long day promotes flowering of Gysophila paniculata L cultivar ‘Bristol Fairy’. Repeated treatments with GA₃ or GA_{4 + 7} in short days did not promote flowering. The long photoperiod is effective only at relatively high temperatures. At night temperatures below 12°C, the plants remain vegetative even in long days. Efficient artificial lighting is from incandescent lamps at 60–100 lux. Fluorescent lighting (Cool-White) is not effective. Lighting of 4 hours as a night-break or at the end of the night were equally effective, but 4 hours lighting as a day-extension was less effective. Whole-night lighting promoted flowering more than any of the 4-hour lighting regimes. Cyclic lighting of one third light in each cycle promoted flowering to the same extent as continuous lighting. Light intensity during the day has a decisive effect on flower production.     

Flower formation in Calceolaria × herbeohybrida Voss

At high light intensity Calceolaria × herbeohybrida ‘Zwerg Meisterstück’ is a long-day plant with a critical day-length of 14–15 h. At low light intensity (e.g. as in winter) flowering will take place if the long-day treatment is preceded by a chilling period (10°C) or by short days at 15–20°C. During the chilling period day-length is of little influence. With increasing duration of the chilling period the requirement for long days decreases and the critical day-length becomes shorter. After a sufficient chilling period, flowering occurs both in long and short days. If the chilling period lasts approx. 40 days, however, flowering in short days is delayed, phyllody occurs and only a small number of flowers develop in comparison to long days. After at least 70–75 days of chilling plants show almost the same reaction in short and long days. Plants not chilled under conditions of high light intensity and short days flower either in naturally long days or by day extension with incandescent light. After chilling, fluorescent light of the type L 39 is also effective for day extension. A night break with incandescent light in a 16-h dark period induces flowering only after a chilling period. Incandescent but not fluorescent light causes a slight yellowing and more upright position of the leaves and an elongation of the internodes.     

Effect of day and night temperatures during long photoperiods on the vegetative growth and flowering of Chrysanthemum morifolium Ramat

The influence of day and night temperatures in the range of 10–17°C on the vegetative growth under long days of 17 year-round cultivars of chrysanthemum was studied. The after-effect of the temperature regime on the time of flowering at 17°C under short days was also recorded.A decrease of the day or night temperature reduced growth, but the effect of the day temperature was much stronger than that of the night temperature. The temperature during the vegetative period had hardly any effect on the time of flowering at 17°C.The consequences for production and breeding are discussed.     

Flowering in pyrethrum (Tanacetum cinerariaefolium L.). I. Environmental requirements

SUMMARY

Floral evocation in pyrethrum {Tanacetum cinerariaefolium) is stimulated by a period of vernalization. Night temperatures of 6°C and 12°C for two weeks and three weeks, respectively, promote rapid inflorescence initiation and development. A night temperature of 18°C does not satisfy the vernalization requirement. Longer periods of vernalization stimulate more rapid inflorescence initiation and development and result in a larger number of inflorescences being initiated. The vernalization stimulus may be modified by the daily light integral. Both inflorescence initiation and inflorescence development are promoted by long days. The number of leaves formed before flower bud initiation is not affected by daylength. Night-break lighting does not promote flowering. It is suggested that the stimulatory effect of long days may be in supplying photosynthetic assimilates to the developing meristems. Floral development is retarded by low photon flux density conditions regardless of day temperature. High day temperatures (25°C) combined with low photon flux (350 umol m"2 s"' or less) prevented pyrethrum from flowering in otherwise inductive conditions.     

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.     

The effects of storage temperature and fruit size on firmness,extractable juice,woolliness and browning in two nectarine cultivars

Fruit firmness, extractable juice, woolliness and browning of the mesocarp tissue in ‘Independence’ and ‘Flavortop’ nectarines stored at —0.5°, 3°, 5° and 7°C for four weeks were determined during ripening at 15°C. The firmness of both ‘Independence’ and ‘Flavortop’ during ripening decreased as storage temperatures increased. The percentage extractable juice after cold storage and during ripening varied considerably between cultivars and between the storage temperatures. The extractable juice of fruit stored at higher temperatures tended to increase during ripening, whereas fruit stored at lower temperatures tended to decrease first before increasing. At storage temperatures of —0.5° and 3°C both cultivars passed through a stage of woolliness during ripening, while less woolliness occurred after storage at 5° and 7°C. In both cultivars the percentage extractable juice during ripening was higher on average at storage temperatures of 5° and 7°C. Severe browning of mesocarp tissue in both cultivars occurred during ripening after storage at 3°C. The effect of fruit size on changes in firmness, development of woolliness and mesocarp browning in ‘Flavortop’ nectarines stored at — 0.5°C for four weeks and ripened at 15°C was also determined. Larger nectarines lost firmness more rapidly, woolliness occurred sooner and the mesocarp tissue was more prone to browning than smaller fruit during ripening.     

Chilling requirements of Paeonia cultivars

Dormant second year potted plants of Paeonia ‘Coral Sunset’, ‘Monsieur Jules Elie’, and ‘Sarah Bernhardt’ were placed into three chilling regimes (constant 1, 4, or 7°C) for different durations (3, 6, 9, or 12 weeks) to ascertain their chilling requirements for shoot and flower production. Chilling was followed by forcing for up to 5 weeks at 18°C, then plants were maintained in a controlled greenhouse until flowering had finished. Mean number of shoots and flowers per plant were recorded and the time taken for shoots to sprout was calculated.Control plants (forced immediately without chilling) produced no shoots or flowers. For all cultivars, the proportion of plants that sprouted, and the mean number of shoots and flowers increased as plants were subjected to colder chilling temperatures, or longer chilling durations. However, there were no significant within-cultivar differences between different treatments of 9 weeks or more. The time taken for sprouting to occur after the completion of each chilling treatment consistently decreased as the duration of the chilling treatment increased. In most cases, lower chilling temperatures lead to more rapid sprouting once plants were placed in the 18°C forcing conditions.When a simple model was fitted where the chilling temperature and duration of each treatment was described by a cumulative normal curve rising from zero to some maximum value (or potential) once adequate chilling had been received, we found that temperatures of 4 and 7°C provided only 83 and 59%, respectively, of the chilling accumulated per unit time at 1°C. ‘Coral Sunset’, an interspecific hybrid early flowering type, required the greatest amount of chilling to sprout consistently, while ‘Sarah Bernhardt’, a very late flowering type, required the least. Of the three cultivars, ‘Sarah Bernhardt’ also required the least amount of chilling to achieve its potential shoot and flower numbers, while ‘Monsieur Jules Elie’, a mid-season flowering type, required the most chilling to achieve the same end for these two variables. This suggests that the response to spring temperatures as well as chilling influences the time of flowering.     

More rapid and uniform germination of Cyclamen persicum L.

Two pre-sowing treatments are described which permit the initial germination processes to proceed but prevent the emergence of any radicles prior to sowing. Such treatments can result in a distinct reduction in the time between sowing and germination and in the length of the germination period. One method employs an aerated osmotic solution, here polyethylene glycol (PEG) ‘6000’ at a water potential of ?8 to ?11 bars at 15°C for 3–5 weeks. The alternative method in which a thermodormancy-enforcing temperature (25–30 °C) is substituted for the osmotic solution is less effective. For best effects, treated seeds should only be surface dried and sown immediately, although some of the effect persists on air drying. It may be necessary to calibrate each batch of seeds for the conditions which advance the germination process as far as possible without permitting actual germination during the treatment.     

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.     

High frequency plant regeneration from microspore-derived embryos of ornamental kale (Brassica oleracea L. var. acephala)

The aim of this work was to study the effect of solid medium, developmental stage, embryonic age, cold treatment and additives to the medium on plant regeneration from microspore-derived embryos in four F₁ hybrids of ornamental kale (Brassica oleracea L. var. acephala). The results showed that all of the cultivars responded best when the embryos were cultured in solidified B5 medium with 1% agar. Optimal regeneration was gained when cotyledonary embryos were cultured for 25 days. Cold treatment significantly improved plant regeneration with a frequency of up to 79.0% under 4 °C for 2 d or 5 d. The addition of 3.0 or 5.0 mg/L silver nitrate (AgNO₃) increased the frequency of plant regeneration. In the Zhouyehongxin cultivar, the frequency of plantlet development reached 84.4%. The addition of activated charcoal reduced embryo hyperhydricity.