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.     

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.     

Flushing and Leaf Growth of Cacao Under Controlled Temperature Conditions

Young clonal cacao trees have been grown for nine months in controlled- environment rooms at 74° F.,80°F. or 86° F. (23·3° C., 26·7° C., or 30·0° C.), or at one of these temperatures during the day and another during the night.

No specific temperature requirements for leaf flushing, which occurred in all the treatments, were found. Flushing was considerably greater at the higher temperatures, partly as a result of the loss of apical dominance, and was especially sensitive to day temperature.

The number of expanded leaves per flush and mean area per leaf increased with a decrease in day or night temperature, as did the duration of the leaves on the trees. The biggest net leaf area increases were made by plants given a day at 80° F. and a night at either 80° F. or 74° F. A night temperature of 86° F. resulted in a rapid turn-over of small unhealthy leaves having a low chlorophyll content.

The gain in total plant dry weight was greatest at a night temperature of 74° F., smallest at a night temperature of 86° F., and the plants which maintained the greatest leaf areas also gained the most dry weight. Leaf dry weight per unit leaf area was greatest at the lowest temperatures, as was the ratio of total plant dry weight to leaf area. The ratio of leaf weight to plant weight showed a small but significant increase with increase in day temperature.     

Temperature effects on flower formation in saffron (Crocus sativus L.)

The temperature conditions for shoot growth and flower formation were characterised for saffron (Crocus sativus L.). Leaf withering occurred during late winter or spring depending on location, and coincided with a rise in temperature. No growth was detectable in the buds during the first 30 days after leaf withering, neither in underground corms nor in lifted corms incubated in the laboratory under controlled conditions. Flower initiation occurred during the first growth stages of the buds. The optimal temperature for flower formation was in the range from 23 to 27 °C, 23 °C temperature being marginally better. To ensure the formation of a maximum number of flowers, the incubation at these temperatures should exceed 50 days, although incubation longer than 150 days resulted in flower abortion. Flower emergence required the transfer of the corms from the conditions of flower formation to a markedly lower temperature (17 °C). Incubation of the corms after lifting at a higher temperature (30 °C), reduced flower initiation and caused the abortion of some of the initiated flowers. No flowers formed in corms incubated at 9 °C. A variable proportion (20–100%) of the corms forced directly at 17 °C without a previous incubation at 23–27 °C formed a single flower. The wide differences in the timing of the phenological stages in different locations we found in this study seemed related to the ambient temperature. Leaf withering was followed shortly by flower initiation, which occurred during late spring or early summer as the rising temperature reached 20 °C. A long hot summer delayed flower emergence which occurred in late autumn as the temperature fell to the range of 15–17 °C.     

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.     

Interactions between root-zone temperature and light levels on growth,development and photosynthesis of Lycopersicon esculentum Mill. cultivar ‘Vendor’

Six-week-old tomato plants were subjected to 5 root-zone temperatures, ranging from 12 to 36°C, and 4 light levels in a factorial design. Large increases in shoot dry weight, leaf area and fruit development resulted from soil warming to 24°C when plants were grown under high light conditions. Shoot growth and fruit weight were reduced at 24°C root temperature under low light conditions. Total plant photosynthesis, leaf area index, net assimilation rates and leaf chlorophyll content were related to plant growth and flower development for the various treatments. Our experiments have shown an interaction between root-zone temperature and light levels for greenhouse tomatoes. Soil warming caused large increases in shoot dry weight and fruit development when light was not limiting plant growth, but had deleterious effects on flowering and fruit set under shaded conditions.     

Influence of the environment on growth and development of chives (Allium schoenoprasum L.). I. Induction of the rest period

The effect of environmental factors on the activity of chive plants has been investigated in model experiments in growth chambers, greenhouses and in the field. The rest period of chives was induced in medium temperatures by short days. The critical day-length was about 14 h, the critical photoperiodically active light intensity about 50 lx. Light intensity in the range of 4–8 klx during the basic light period has no clear influence on the induction of the rest period, but darkness prevents it. The active temperature for the induction of the rest period ranged from over 6 to below 20° C with an optimum at 14° C. Low temperature (below 6° C) preserved, or even promoted, activity of the plants. Changing day/night temperatures act approximately like the constant mean of the day and night temperatures. The action was slightly promoted by a very high amplitude within the range 6–22° C.The necessary duration of the induction period ranged from 4 weeks for a partial, to 8 weeks for a full induction of the rest period. The induction was retarded by dryness. The inductive conditions worked out in the growth chambers agree well with those prevailing in the field during the induction period. For early leaf production in autumn, chives can be kept active by a long day or by storage at low temperature, provided that necroses at the tops of the cuts of the old leaves do not lead to objections at the market. For production of undamaged, newly grown leaves the induction of the rest period is necessary.     

Temperature and development in Iris × hollandica during preplanting storage. I. Leaf initiation

Summary

Leaf initiation was examined in Dutch iris bulbs during pre-planting storage temperature treatments in the dark. The number of leaves initiated before inflorescence evocation increased with increasing temperature. The base, optimum and maximum temperature for leaf initiation were established as –0.4, 13.1 and 26.7°C respectively. The rate of leaf initiation was shown to be linearly related to temperature. The average thermal-time required for each leaf to be initiated under constant temperatures was 79°Cd but leaves initiated during the transfer temperature treatments required an average of 92°Cd. Rates of leaf initiation predicted from thermal-time equations were similar to those observed in bulbs stored at the lower temperatures (2–13°C) but rates observed at warmer temperature (17–25°C) never reached the predicted high value.     

Effect of photoperiod and light integral on flowering and growth of Eustoma grandiflorum (Raf.) Shinn.

The aim of the study was to examine the effects of different photoperiod and light integral on floral initiation, development and subsequent growth of Eustoma grandiflorum (Raf.) Shinn. Six-weeks-old seedlings of ‘Echo Blue’ and ‘Fuji Deep Blue’ were placed under short day (SD, 10 h) and were transferred to long days (LD, 20 h) at 2-week intervals from 6 to 14 weeks after seeding. Plants initiated flower buds regardless of light regimes. Flower bud initiation was delayed by SD compared to LD; plants transferred after 6 weeks from seeding initiated flower buds at least 21 and 10 days earlier at LD at high (HL) and low (LL) daily light integral, respectively, compared to those at SD. Light regimes had little or no effect on time to flower bud development after initiation. Thus, it seems likely that LD and HL affected the initiation rather than development. Both the photoperiod and light integral strongly influenced the subsequent growth after initiation. SD delayed the time to visible bud (VB), increased the number of nodes to first open flower, number of branches, stem diameter and shoot dry weight compared to LD. HL promoted flowering and increased several shoot characteristics and flowering compared to LL.The results indicate that Eustoma is a quantitative long-day plant. LD, and more specifically HL, enhanced flower bud initiation, development and subsequent growth. An initial SD period is preferred to increase the number of branches, number of flowering buds and flowers, stem diameter and shoot dry weight.     

Response of the chrysanthemum to soil heating

Chrysanthemum plants were exposed to 16°C day-temperature, 11°C night-temperature, 13°C soil-temperature, to be indicated as 16/11/13°C, or to 16/11/25°C, 20/16/18°C, or 20/16/25°C, first long day, then short day, (long day = 12-h light period with 3-h night break; short day = 12-h light period) from planting to harvest in controlled environments to study the effects of soil heating on growth and flowering. There were significant, but not substantial, effects of soil heating on leaf area, percent soluble carbohydrate, flower bud diameter, days to visible bud and some other parameters. Two winter cultivars responded similarly, while 2 summer cultivars differed in flowering-response to soil heating. An experiment was also conducted using 16/11/25°C day/night/soil temperatures during long days, short days or throughout the complete growth cycle, with 16/11/13°C day/night/soil temperatures at other times. Soil heating during long days resulted in the highest quality flowers. Soil heating during short days or throughout the growth period resulted in most rapid flowering but decreased flower quality.     

Increasing Flower Number in Single-Truss Tomatoes

Flower number in the first truss (inflorescence) of glasshouse tomatoes was increased by growing the seedlings at low temperatures shortly after pricking off. The optimal timing for this treatment varied by only a few days over most of the year. The longest chilling duration (14 days) was most effective, possibly because of variability between plants. In summer flower number could be doubled, but in winter only 30% to 40% increases were obtained. Chilling delayed anthesis by up to ten days, the delay being proportional to the duration of chilling.

Day/night temperatures of either 10°/10° C. or 16°/4° C. during chilling had similar effects on flowering, and resulted in similar delays to growth and anthesis.

The mechanism by which chilling may increase flower number and the distinctions between this process and vernalization are discussed.     

Factors Controlling Flowering in Seed-Raised Freesia Plants

The effect of plant age, temperature and day-length on flower initiation and development in “ K. & M. Super ” freesias has been studied.

The flowering response decreased with increasing temperature and the critical temperature for flower initiation was found to be about 21°C. An interaction of plant age, temperature, and duration of treatment was present. Short days (9 hrs.) slightly stimulated flower initiation in“ Yellow K. & M. Super” but delayed it in “ Blue K. & M. Super” freesias. Short-day treatment in the open during the summer had no significant effect, whereas shading markedly hastened flowering.

Flowering could be initiated at an early stage, but older plants were more responsive, especially those of “Blue K. & M. Super”. Optimum temperatures for flower initiation were 12-15°C., applied for 6-9 weeks after the plants had formed about seven visible leaves.

Abnormal inflorescences in freesias, recognized by enlarged bracts and irregular spacing of the florets (so-called “gladiolus-like flowers”), appeared to result from incomplete flower initiation. In extreme cases flower stalks without any flowers were formed. In order to avoid such abnormal flowering it was important that the first floret in the inflorescence should have reached a certain stage (P₂) of development before low-temperature treatment was discontinued.     

Apple Rootstock Studies: Thirty-Five Years’ Results with Cox’s orange Pippin on Clonal Rootstocks

With the aim of obtaining information about light and temperature relationships during the early weeks of growth of young tomato plants, measurements of the weekly dry weight increments were made with plants up to six weeks old. Growth took place in natural light conditions during a number of winter periods (October to March). The daily light-time integrals (foot candle hours) were recorded throughout the investigation. In three experiments, each extending over a whole winter period, plants were grown at one-day temperature, but at three levels of night temperature, namely (a) 4° F. lower than the day, (6) equal with the day, and (c) 4° F. higher than the day. The day temperature was 6o° F. (15 ? 5° C.), 64° F. (68°C.) and 68°F. (20°C.) respectively for the three experiments. The results are summarized as follows :

1. With each day temperature, growth rates were lowest when night temperature was lower than the day.

2. Comparison of the effects of the constant temperature regimes with the high night temperature regimes showed that with the day temperature at 60° F. the growth rate was generally higher when the night temperature was high. With higher day temperatures, however, this was not the case.

3. There was little evidence that over this temperature range the temperature inducing maximum growth was related either to the light conditions or to the age of the plant.

4. The response to night temperature was small by comparison with response to that of the day.

5. The results suggest that in winter highest growth rates will be achieved if the night temperature is not lower than 64° F. and the day not lower than 68° F.

The results of an experiment designed to evaluate the separate effects of day and night temperatures showed that, over the temperature range 6o° F. to 68° F., dry weight increased with the night temperature. However, a much larger increase resulted with a comparable temperature rise during the day. Stem length was unaffected by the level of the night temperature but increased markedly with the day temperature.

The periods from pricking-out to both initiation and anthesis of the first two inflorescences were recorded for plants growing at 6o° F., 64° F. and 68° F. The temperature effect on the period to initiation was small. The inverse relationship between temperature and the period to anthesis was especially marked in low light conditions.

The value of adjusting both the day and night temperatures in accordance with the day-to-day fluctuations of the natural light was assessed by comparison with other temperature regimes having the same mean over each 24 hours. In general, flowering and fruiting was earliest when the day and night temperatures were equal. No evidence was found to justify the technique of adjusting the temperature in accordance with the natural light.     

Day and night temperatures,daily light integral,and CO2 enrichment affect growth and flower development of Campanula carpatica ‘Blue Clips’

Campanula carpatica Jacq. ‘Blue Clips’ plants were grown in a greenhouse under nine combinations of day and night temperatures created by moving plants every 12 h among three day/night temperatures (15, 20, and 25°C). At each temperature, there were three daily light integrals (DLI; 4.2, 10.8, and 15.8 mol m⁻² per day, averaged over the experimental period) created with varying supplemental light, and ambient (≈400 μmol mol⁻¹) and enriched (≈600 μmol mol⁻¹) CO₂ concentrations. Time to flower was closely related to average daily temperature (ADT), and was not significantly affected by the day or night temperatures delivered to achieve a specific ADT. Time to flower was not largely affected by DLI or CO₂ enrichment. As plant ADT increased between 15 and 25°C, flower diameter decreased about 1 mm per degree and was not related to the difference between day and night temperatures (DIF). Flower diameter was smallest and least sensitive to changes in temperature at lower DLI and at ambient CO₂ levels. There were 10 less flower buds and 0.3 g less dry mass per plant at first flower for every 1° increase in plant ADT at high and medium DLIs. Flower bud number and dry mass were relatively low and less sensitive to changes in ADT at low DLI, and increased slightly with CO₂ enrichment at medium and high but not at low DLI. Plant height was not related to ADT, but increased linearly as DIF increased from −6 to 12°C at all DLIs, but the response was stronger under low DLI than high and medium DLIs. Flower bud number and dry mass were correlated closely with the ratio of DLI to daily thermal time (base temperature of 0°C). Flower bud number and dry mass were highest when C. carpatica plants were grown at 15°C with a DLI of 10–15 mol m⁻² per day.     

Flowering in pyrethrum (Tanacetum cinerariaefolium L.). II. Changes in plant growth regulator concentrations

Radioimmunoassays were used to quantify the endogenous concentrations of plant growth regulators (PGRs) in pyrethrum during flower initiation and development. The concentrations of gibberellins, abscisic acid, indole acetic acid, zeatin and zeatin riboside, dihydrozeatin and dihydrozeatin riboside, and isopentenyladenine and isopentyladenosine were assayed. Fluctuations in PGR concentrations were correlated with flower bud initiation, flower stem elongation and floral differentiation. The gibberellin concentration increased during vernalization (6°C night temperature), a treatment known to promote floral initiation. A marked increase in gibberellin concentration was correlated with the onset of flower stem elongation. The concentration of the auxin indole acetic acid declined significantly at this time and remained low during flower bud development. Low photon flux density conditions, which retard floral initiation in otherwise inductive vernalizing conditions, failed to induce a decrease in indole acetic acid concentration.     

Environmental and chemical control of growth and flowering of Chamelaucium uncinatum Schauer

The main factor affecting floral initiation of Geraldton Wax-Flower (Chamelaucium uncinatum) is the photoperiod, while temperature is the major factor affecting flower development. Four weeks of short days (SD) are generally required for obtaining full flowering. The number of flowers produced per plant increases with increasing the number of SD. Under mild temperatures of $\text{20}\text{14°}\text{C}$ (day/night), plants initiated flowers even in long days (LD). However, fewer flowers were produced and on higher nodes as compared to SD plants. Chlormequat promoted flowering under prevailing summer conditions of high temperatures and LD. Under prevailing autumn conditions favourable for flower initiation, LD treatment or weekly sprays with gibberellic acid (GA) reduced the number of flowers per plant. Combined treatment of LD and GA reduced both the flowering percentage and the number of flowers per plant. Discontinuing the LD or the GA treatments caused a resumption of full flower initiation.     

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.     

Manipulation of bolting and flowering in celery (Apium graveolens L. var. dulce). II. Juvenility

After germination, a juvenile phase of development was apparent in cvs New Dwarf White and Celebrity. During this incompetent phase, plants were not induced flower even when subjected to chilling at 5°C for nine weeks. Juvenility ended and the plants became competent to perceive chilling as a vernalization stimulus when they had initiated 17 leaves including leaf primordia in cv. New Dwarf White and between 17 and 20 leaves in cv. Celebrity. After phase transition, the level of competence was not affected by plant age. The rate of leaf initiation in cv. New Dwarf White during juvenile and competent vegetative growth related linearly to temperature, increasing between 3 and 22.8°C and then declining over the range 22.8 to 37.4°C. The first 17 leaves of celery cv. New Dwarf White had longer plastochrons of 43° Cd (>3°C) each than subsequently initiated leaves with 29° Cd for each leaf. The thermal time requirement for completion of juvenile development after radicle emergence was 731° Cd> 3°C. In cv. Celebrity the first 17 leaves required 42° Cd each for initiation.     

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.     

Promotion of floral initiation in ‘Fuerte’ avocado by low temperature and short daylength

Potted avocado (Persea americana Mill., cv. ‘Fuerte’) plants were maintained in growth cabinets for up to 32 weeks and new growth observed for flower formation. Flowers were formed if temperatures were 20°C or below, but with 25° or 30°, even if only for 1 hour per day, flower formation was inhibited. Time to flowering was accelerated, but number of flowers reduced, if daylength was shortened from 15 h to 9 h. With low temperature and short days, full bloom was about 4 months after starting experiments. Spring flowering of cv. ‘Fuerte’ in the field could follow flower induction about 4 months previously with the onset of winter temperatures and daylengths.