Environmental interaction between day length,night temperature,and photon flux density on growth and flowering in Boronia megastigma Nees.

Summary

Boronia plants were placed in a range of environmental conditions, two night temperatures (6 and 15°C), three photon flux densities (full sunlight, 50% and 30%), and two day lengths (natural autumn to winter cycle and natural autumn to winter cycle plus synthetic to 16 h total light). Flowering occurred to some extent under all conditions; generally conditions suitable for high growth rates were not optimum for flowering, maximum numbers of flowers were achieved with low night temperatures (6°C), short days (10 h), and full to 50% sunlight. Floral development was influenced by all treatments.     

Changes in apical morphology during floral initiation and development in pyrethrum (Tanacetum cinerariaefolium L.)

Summary

Changes in apical morphology during floral initiation and development in pyrethrum (Tanacetum cinerariaefolium L.) were investigated by scanning electron microscopy. The sequence of events may be divided into eleven stages of apical development which are distinctive in both morphology and size. The environmental stimulus promoting rapid flower initiation was demonstrated to be vernalization. Flower initiation occurred after four months under non-vernalizing conditions through an autonomous flower induction process. Devernalization was observed under short day (10 h daylength), low photon flux density (200 µmol m² s^?1) conditions. Apices were never observed to revert to vegetative growth after the initiation of the first involucral bract and therefore this was considered to be the developmental stage at which the apex was committed to generative development.     

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.     

Effect of photoperiods before,during and after vernalization on flower initiation and development and its varietal difference in Japanese bunching onion (Allium fistulosum L.)

Summary

To control the bolting of Japanese bunching onion (Allium fistulosum L.) photoperiodically, the effect of photoperiods before, during and after vernalization on flower initiation and development and the varietal differences were investigated using the two mid-season flowering cvs Kincho and Asagi-kujo, and a late-season flowering cv. Cho-etsu. A long-day photoperiod (LD, 16 h) given before vernalization inhibited flower initiation. Especially, the bolting rate of ‘Asagi-kujo’ decreased by about a half, compared with the short-day photoperiod (SD, 8 h). The interaction between the effect of night temperature (3°C, 7°C, 11°C or 15°C) and the effect of the photoperiod (SD and LD) during vernalization was also investigated. In ‘Kincho’, LD did not affect flower initiation at 3°C, but inhibited flower initiation at 7°C, 11°C and 15°C. In ‘Asagi-kujo’, flower initiation was significantly inhibited by LD under all temperature conditions. This inhibitory effect was stronger at 11°C and 15°C than at 3°C and 7°C. In ‘Cho- etsu’, LD significantly inhibited flower initiation at 3°C and 7°C, and flower initiation rarely occurred at 11°C and 15°C. In this study, generally, LD during vernalization inhibited flower initiation in all cultivars. Thus Japanese bunching onion required a short-day photoperiod in flower initiation, which was stronger in ‘Asagi-kujo’ and ‘Cho-etsu’ than in ‘Kincho’. From these results, we conclude that low temperature and a short-day photoperiod complementarily induce flower initiation in Japanese bunching onion. Varietal differences exist in the requirement of low temperature and a short-day photoperiod: the primary requirement in ‘Kincho’ is low temperature and that in ‘Asagi-kujo’ is a short-day. After flower initiation, the early stage of flower development is day-neutral, and after the floret formation stage, a long-day photoperiod promotes flower development and elongation of the seedstalk.     

Effect of temperature on growth and flowering of litchi (Litchi chinensis Sonn.) cultivars

Summary

Moderate day/night temperatures (20/15° v. 15/10°C) increased vegetative growth and reduced flowering in the seven litchi cvs Tai So, Bengal, Souey Tung, Kwai May Pink, Kwai May Red, Salathiel and Wai Chee. At higher temperatures (25/20° and 30/25°C), vegetative growth was promoted further and flowering eliminated. Temperature also influenced the type of inflorescence formed. More leaves were formed on the panicles of trees growing at 20/15° than at 15/10°C. All terminal shoots on all cultivars produced panicles at 15/10°C. The relative order for the amount of flowering at 20/15°C was: ‘Wai Chee’>‘Salathiel’>‘Kwai May Pink’>‘Tai So’>‘Bengal’>‘Souey Tung’>‘Kwai May Red’. Cultivars which were vigorous at high temperatures produced fewer panicles at 20/15°C and fewer leafless panicles at 15/10°C. Only small differences were observed in the leaf water potential and the nutrient status of the shoots at different temperatures. Vigour and flowering of the cultivars in the glasshouse generally reflected field performance in subtropical Australia (Lat. 27°S). Low vigour could be useful for selecting litchi cultivars for good fruiting in environments with warm autumns and winters.     

The effects of day and night temperature on Chrysanthemum morifolium: investigating the safe limits for temperature integration

Summary

The impact of day and night temperatures on pot chrysanthemum (cultivars ‘Covington’ and ‘Irvine’) was assessed by exposing cuttings, stuck in weeks 39, 44, and 49, to different temperature regimes in short-days. Glasshouse heating set-points of 12°, 15°, 18°, and 21°C, were used during the day, with venting at 2°C above these set-points. Night temperatures were then automatically manipulated to ensure that all of the treatments achieved similar mean diurnal temperatures. Plants were grown according to commercial practice and the experiment was repeated over 2 years. Increasing the day temperature from approx. 19°C to 21°C, and compensating by reducing the night temperature, did not have a significant impact on flowering time, although plant height was increased. This suggests that a temperature integration strategy which involves higher vent temperatures, and exploiting solar gain to give higher than normal day temperatures, should have minimal impact on crop scheduling. However, lowering the day-time temperature to approx. 16°C, and compensating with a warmer night, delayed flowering by up to 2 weeks. Therefore, a strategy whereby, in Winter, more heat is added at night under a thermally-efficient blackout screen may result in flowering delays. Transfers between the temperature regimes showed that the flowering delays were proportional to the amount of time spent in a low day-time temperature regime. Plants flowered at the same time, irrespective of whether they were transferred on a 1-, 2-, or 4-week cycle.     

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.     

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.     

A model for leaf production and apex development in calabrese

Summary

A single, temperature based model was developed, accounting for both leaf initiation and changes in the apex diameter of calabrese cv. Shogun associated with vernalization. The model was derived using data from an experiment in controlled environment cabinets, which had ten constant temperatures between 7.3 and 22.6°C. It was tested on data from 20 field-grown crops of cvs Shogun and Corvet and 24 treatments of an experiment in growing rooms involving transfer of plants between different temperatures. The model predicted changes in both number of leaves and apex diameter of field plants accurately, except for some early values. In growth rooms, predictions were accurate for nearly all treatments. Simulation of leaf production and apex development for 100 d at temperatures from 0 to 35°C, predicted that apex initiation would not occur at 0, 30 and 35°C, and would take 96, 51, 36 and 64 d respectively at 5,10,15 and 20°C.     

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.     

Flowering and bolting in carrot. II. Prediction in growth room,glasshouse and field environments

Rates of bolting and flowering in carrots cv. Chantenay Red Cored, measured as the reciprocals of days to first internode visibility and flower bud appearance respectively, were shown to relate linearly to a thermal time of vernalization derived from data obtained in controlled environments. Days elapsed from the end of vernalization to the start of visible bolting and flowering bore a curved relationship to thermal time of vernalization. The model curves also predicted closely the bolting and flowering responses of carrots to vernalization at different temperatures in controlled environments and under markedly different conditions in the field. Time taken from the end of vernalization to flowering and bolting decreased with increasing thermal time of vernalization, particularly between ca. 110 and 400°Cd. Vernalization beyond 400°Cd had less effect on the timing of these processes. The percentage of plants flowering increased asymptotically with increasing thermal time of vernalization up to ca. 400°Cd whereas shoot extension increased linearly up to ca. 650°Cd.     

Inhibition of flowering of Mexican- and Guatemalan-type avocados under tropical conditions

Avocado trees of a range of cultivars growing in Darwin, northern Australia (average yearly maximum 33°C, minimum 23°C), were observed for flower and shoot development. Terminal buds of the cultivars ‘Fuerte’, ‘Rincon’ and ‘Edranol’ sampled in July were not floral. Buds which did not burst were sampled in September and they contained developing flowers with perianth primordia. Vegetative extension growth resulted from laterals proximal to the inhibited terminal buds.Avocado trees of the cultivars ‘Fuerte’ and ‘Hass’ which had initiated floral buds were transferred to controlled environment chambers with 33°C day, 23°C night ($\text{33}\text{23}$) or 25°C day, 15°C night ($\text{25}\text{15}$) with a 12-h photoperiod and photon flux density of 400 μmol m^?2 s^?1 (400–700 nm). At $\text{33}\text{23}$ the trees had fewer flowers and a shorter flowering period than at $\text{25}\text{15}$. Inhibited floral buds and lateral vegetative extension resulted at $\text{33}\text{23}$, as observed in northern Australia. The unburst buds had developing flowers with perianth and stamen primordia.The controlled environment experiments showed that the abnormal flushing behaviour of Mexican- and Guatemalan-type avocados growing in northern Australia was due to high temperature. Floral development was inhibited at the stage of stamen differentiation.     

Flower formation of Chinese cabbage. I. Response to vernalization and photoperiods

The influence of temperature, vernalization duration and photoperiods on the leaf number and beginning of bolting of Chinese cabbage was tested in growth chambers. An increasing effect of vernalization was indicated by decreasing leaf number and premature bolting. Sensitiveness for vernalization started with germination and remained constant with increasing plant age. During their development on mother plants, seeds were not vernalized.Inductive temperature ranged between 0 and 20°C. The necessary vernalization duration was lowest at 5–8°C. For slight vernalization effects one week was sufficient; for complete vernalization about 3 weeks were needed. To achieve the same effect, the necessary vernalization duration increased considerably at temperatures below 5°C, but increased only slightly at temperatures above 8°C.Long days promoted bolting when the temperature rose after incomplete vernalization. In constant low or high temperature, no photoperiodic effect was perceptible.     

Vernalization promotes flowering of a heat tolerant Calandrinia while long days replace vernalization for early flowering of Brunonia

The flowering responses of Brunonia australis (blue pincushion) and Calandrinia sp. to vernalization, photoperiod, temperature and plant age were investigated to provide a foundation for manipulating flowering in these potential potted plants. Plants were vernalized at 4.8 °C for 0, 3 or 6 weeks at the plant age of 1–4 or 8–14 leaves. Following vernalization, plants were grown at 25/10 or 35/20 °C (day/night) under short days (11 h, ambient daylight averaged 380 ± 44 μmol m⁻² s⁻¹) or long days (16 h) provided by an additional 5 h night break (21:00–2:00 h at <4.5 μmol m⁻² s⁻¹ from incandescent lamps), for 85 days. This is the first work to investigate flowering of these ornamental species. Both species showed enhanced flowering following vernalization and a quantitative requirement for long days. The reduction of the time until the first visible inflorescence (Brunonia) or flower (Calandrinia) buds by 8–13 days was affected by vernalization for 3 or 6 weeks, respectively. Long days were effective for reducing the time to first visible floral bud and increasing the number of inflorescence or flowers per plant for both species. For Brunonia, LDs replaced vernalization when applied to plants with 1–4 leaves. Raising temperature from 25/10 to 35/20 °C increased the number of flowers per plant of Calandrinia by 2–2.5-fold for plants with 1–4 or 8–14 leaves respectively.     

Optimization of agrotechniques in the cultivation of Luffa acutangula

Germination requirements, flowering pattern, planting density and growing regimes were examined for Luffa acutangula (L.) Roxb. Maximum germination (50%) was obtained at 35°C, and at 8, 12, and 45°C germination was completely inhibited. Partial removal of the seed coat increased the percentage of germination while vernalization and exposure to salinity 5=50 mM NaCl reduced it. Planting season influenced flowering pattern, with significantly more female flowers being produced in spring-summer (long days and high temperatures) than in autumn-winter (short days and low temperatures). A high yield of 44.5-47.3 Mg ha 1 was obtained for plants trained on trellises at planting densities of 10,000 and 20,000 plants ha-1. Fruits kept at low temperatures showed the least deterioration during storage, a shelf life of about two weeks being demonstrated at 4°C.     

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.     

Manipulation of bolting and flowering in celery (Apium graveolens L. var. dulce). III. Effects of photoperiod and irradiance

SUMMARY

Photoperiods of 8 and 16 h during chilling at 5°C had no effect on bolting and macroscopic flower appearance in celery cv. New Dwarf White. Eight hour photoperiods during chilling however markedly increased the number of plants forming sessile flowers. Short photoperiods (8 h) after chilling decreased the proportion of young, but competent plants that bolted and flowered. Total darkness during chilling completely prevented any subsequent vernalization response either as bolting or as flowering. Reducing irradiance receipt by the plants during chilling from 85 to W m"2 (PAR) had no effect on their vernalization response. After chilling, a reduction in mean daily total irradiance in the glasshouse from 4.05 to 1.57 MJ m"2 d-1 had no effect on bolting and flowering. Confinement of competent plants to darkness for 4-8 d at 20°C just prior to chilling resulted in a highly significant delay (F>0.001) to bolting and reduced the number of plants flowering. Two days of darkness had no significant effect. The inhibitory effects of dark treatments prior to chilling was greater in plants chilled subsequently for six weeks than for nine weeks.     

Effect of temperature on inflorescence development and sex expression of mono- and poly-embryonic mango (Mangifera indica L.) cultivars

Summary

The effect of temperature on inflorescence development and sex expression in two mono-embryonic (`Irwin' and `Sensation'), and two poly-embryonic (`Nam Dok Mai' and `Kensington') mango cultivars was studied. Trees were subjected to natural winter temperatures to induce flowering prior to transfer into controlled environment glasshouse rooms under day/night temperature regimes of 15/5, 20/10, 25/15 and 30/208C for 20 weeks. Inflorescence development did not progress when trees were held at 15/58C. Cooler temperatures (20/108C) delayed the start of anthesis (42.4.d) compared with trees grown at 25/158C (23.d) and 30/208C (16.1.d). At 20/108C, the delay in the start of anthesis was greatest for `Sensation' (55.5.d) and least for `Nam Dok Mai' (25.5.d) while at other temperatures there was little difference between cultivars. The distribution of hermaphrodite flowers within the inflorescence was independent of temperature with the highest percentage found in the apical half of the inflorescence. There was an inverse relationship between the length of the anthesis period and temperature, with anthesis occurring over 30.d at 20/108C and reducing to fewer than 10.d at 30/208C. Temperature also had an inverse effect on the total number of flowers per inflorescence with 619.6.6.108.0 (mean for all cultivars) at 20/108C decreasing to 431.3.6.80.5 at 30/208C.     

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.