Prevention of hot-water treatment damage in narcissus bulbs by pre-warming

Summary

Hot-water treatment (HWT) used to control stem nematode in narcissus bulbs can lead to yield loss through damage to flower, leaf and root initials. Warm storage of bulbs, usually at 30°C, reduces this damage. The effects of two pre-warming treatments (18°C for two weeks or 30°C for one week before HWT) were investigated in bulbs hot-water treated at a range of dates (from early-July to late-September). Experiment 1 was conducted on bulbs of cv. Carlton lifted on three dates. In the year after HWT, flower numbers were much reduced when HWT was applied after mid-August following storage at ambient temperatures, or after late-August following storage at 30°C, but numbers were only slightly reduced even with late-September HWT when given after 18°C storage. Pre-warming was somewhat more effective after early lifting. Late HWT reduced yields of bulbs harvested after two years' growth, but 18°C treatment largely prevented these losses. In Experiment 2, the beneficial effects of 18°C treatment were confirmed in cvs Carlton and Golden Harvest but not in cv. Barrett Browning. These findings are discussed in terms of growth retardation by warm temperatures.     

Factors affecting the response of tulips to gibberellin

Gibberellic acid (GA₃) treatment of forced tulip crops has potential for producing faster growth to anthesis in the glasshouse, for reducing losses due to floral bud blasting, and for reducing the duration of cold storage needed to obtain satisfactory flowers. Using partly and fully cooled direct-forced tulips, cultivar ‘Apeldoorn’, several factors (relevant to the definition of GA₃ treatments) were studied. Experiments confirmed the previously recorded effects of gibberellins in tulips: GA₃ injections reduced the duration of the glasshouse period, enhanced flower survival and flower length, and reduced stem length at flowering.Following bulb storage at temperatures from ?2 to 20°C, GA₃ reduced the glasshouse period by 15–25% and increased flower length, compared to controls, irrespective of storage temperature. Stem length was also reduced by GA₃, this effect being greater following a storage temperature of 5°C or lower. When GA₃ was applied during the period of 17°C-storage which precedes cool storage, or during or after storage at 5°C, it was found that treatments during or at the end of cool storage were more effective in producing the characteristic effects of GA₃ than were pre-cooling applications. In partly cooled bulbs (but not fully cooled ones), the GA₃-induced earliness of flowering was about doubled when GA₃ injections were given repeatedly at 2-week intervals throughout storage. The responses to GA₃ injections were found to be unmodified by early-lifting and heat-treatment (for earlier forcing), by delaying the start of 5°C storage (for later forcing), by glasshouse temperature (16 and 18°C), and by shading treatments; there was little effect of bulb size.     

The prevention of “three-leaved plants” in the forcing of iris × hollandica by early heat treatment of stored bulbs or by ethephon field spraying

The number of non-flowering three-leaved plants occurring in the forcing of Iris ‘Wedgwood’ and Iris ‘Ideal’ can be drastically reduced if the bulbs are lifted several weeks before the normal lifting time and receive a 10-day 30°-treatment prior to the standard treatment for early flowering. The early lifting, however, leads to an appreciable reduction of the yield.An ethephon spray applied to the plants in the field several weeks before they die has a similar effect without the consequence of reduced yield because the bulbs can be lifted at normal time.     

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.     

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.     

The growth and flowering of Hymenocallis × festalis

Bulbs of Hymenocallis (including Ismene) have showy, fragrant flowers. Little is known of the horticultural potential of these plants, and observations and trials on a stock of Hymenocallis × festalis are described.

In a stock of glasshouse-raised bulbs, bulb grade exerted a marked effect of the number of florets produced, which increased from 2 in 9–10-cm-circumference bulbs, to 7 in 18–19-cm-grade bulbs. Field-raised bulbs of the same grades produced fewer florets. Bulbs were usually planted for flower production in the glasshouse in April; earlier planting (February) leading to greater floret size but a longer period in the glasshouse before anthesis. Planting could be delayed at least until June, or later flowering could be achieved by storing the dry bulbs over winter at a low temperature (5°C), but the latter treatment reduced the percentage of bulbs which flowered. The long scapes could be dwarfed by ethephon (as Ethrel). Hot-water treatment, as a pest and disease control measure, did not result in damage to the flowers provided it was delayed until after the staminal cup initial had been formed.

In the field, growth of the main bulb was more vigorous than in the glasshouse, but pot culture in the glasshouse led to copious offset production. Data are presented for bulb increases for various grades of bulbs planted in outdoor beds at rates of 350–1050 g per metre row.     

Effect of precooling at 5 or −1°C on shoot growth,flowering and carbohydrate metabolism in tulip bulbs

Precooling of dry tulip bulbs at ?1°C may be advantageous, compared with precooling at 5°C. Increasing the duration of precooling enhanced the growth of the shoots after planting, improved flower quality, and reduced the number of days to flower. The positive benefit of a stepwise precooling (5°C for 3 weeks, then ?1°C) was evident.Shoot elongation was promoted, and number of days to flower was reduced when the bulbs were precooled at ?1°C for less than 12 weeks. Extension of precooling beyond 12 weeks, however, was more effective with 5°C precooling. With few exceptions, sufficient precooling at either 5 or ?1°C gave a high percentage of flowering plants with first-quality flowers. Short durations (6–8 weeks) of precooling sometimes promoted flower blasting.Precooling at 5 or ?1°C had a similar effect upon the carbohydrate interconversion in scales and shoots of the bulbs, which as a rule is more pronounced at the lower temperature. The shoots accumulated sucrose, and to some extent fructosyl sucroses, during the 15 weeks precooling. Starch was also accumulated, the highest concentration being obtained at 5°C. The amount of starch was reduced in the scales during precooling, while the concentration of sucrose and fructosyl sucroses increased to a maximum value and then slowly diminished after about 9 weeks of precooling. The monosaccharides, glucose and fructose showed very small variations.     

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.     

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.     

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.     

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.     

Flower-bud formation and shoot growth in apple as affected by temperature

Under controlled conditions, 3-year old ‘Golden Delicious’ and ‘Cox's Orange Pippin’ trees were exposed to 2 temperatures (high: 24° and low: 17° or 19° C) in various treatments in a 4-month period starting at full bloom. In general, shoot growth was reduced at the low temperature. For ‘Golden Delicious’ flowering did not respond to the various treatments; in ‘Cox's Orange Pippin’ it was stimulated at the low temperature.A rise in temperature from 17° to 24° C seven weeks before harvest, given to ‘Cox's Orange Pippin’ trees kept at 17° C from full bloom, reduced flower-bud formation and stimulated growth. A similar temperature increase applied to trees maintained at 24° C for 4–5 weeks after full bloom favoured flower-bud formation, but did not affect growth.The inhibitory effect of the high temperature on flowering is discussed in terms of an increase of the plastochron under the influence of gibberellins produced by the growing shoot tips.     

Effects of exposure of bulbs to smoke and ethylene on flowering of Narcissus tazetta cultivar ‘Grand Soleil d'Or’

Bulbs of ‘Soleil d'Or’, exposed to smoke generated from smouldering wood and fresh leaves for several hours on each of 4 consecutive days during storage, produced flowers earlier and at a higher rate, even when using bulbs which were too small to flower using normal methods. The smoked bulbs showed an earlier start of floral initiation and faster development. A temperature of 25°C was optimal for storage. Application of ethylene also gave similar promotive effects when repeated 4 times at 10 μl 1^?1 for 1–5 h per day. Longer exposure to ethylene or smoke was less effective or had no promotive effect.     

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.     

An analysis of the growth of forced tulips. 1. Changes in plant fresh and dry weights during growth at two temperatures

Changes in the fresh and dry weights of the component parts of plants of tulip cv. ‘Apeldoorn’ were followed in bulbs kept at low and high temperatures (9 and 18°C respectively) from the time of completion of flower differentiation until anthesis.There were marked differences between shoot dry weights at the two temperatures. At 9°C the stem, leaves and flower grew exponentially throughout the whole period, but at 18°C the specific growth rate of the stem and leaves declined throughout the period of the experiment. At 9°C the proportion of total dry weight in shoots and daughter bulbs was higher than at 18°C, and the proportion in the mother bulb was correspondingly smaller.At both temperatures the $\text{fresh weight}\text{dry weight}$ ratios of the mother bulb, shoot and daughter bulbs declined during dry storage, the decline being greater at 9°C. After planting, the ratio for all plant parts increased at 9°C, but scarcely changed at 18°C.These results are discussed in relation to dormancy, to the low-temperature requirement for successful and rapid flowering and to flower quality.     

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.     

Starch content of freeze-dried anthers and α-amylase activity of their extracts as criteria that dry-stored bulbs (Tulipa gesneriana, L.) cultivar ‘Apeldoorn’ have been exposed to 5°C

Starch and sucrose were estimated selectively in freeze-dried anthers from tulip bulbs pre-cooled at 5°C for 12 weeks and from a control batch maintained at 17°C. α-Amylase activity in anther extracts was also estimated. Based on data from our own trials (1981, 1982 and 1983) and from 18 batches from typical bulb-producing regions in The Netherlands (year 1983), sucrose was discarded as indicator. The following tentative criteria are proposed for detecting whether dry bulbs cultivar ‘Apeldoorn’ have been exposed to 5°C: starch content of freeze-dried anthers should exceed 10% and specific activity of α-amylase should be below 0.16 (arbitrary unit per mg protein). These criteria are not indicative of the duration of the 5°C period.     

Flower-bud formation in apple under various day and night temperature-regimes

Starting at full bloom, 4 temperature treatments were applied to 3-year-old ‘Golden Delicious’ and ‘Cox's Orange Pippin’ trees. Either 17 or 24° C were applied in 3 successive periods of 5–6 weeks each.In ‘Golden Delicious’, exposure to 24° C during the first 5 weeks after full bloom enhanced shoot growth and reduced flower-bud formation in spur buds. The difference in temperature-regime during the third period did not affect either growth or flowering. Almost all apical shoot buds became floral, irrespective of treatment.‘Cox's Orange Pippin’ trees maintained at 24° C throughout grew more vigorously than did those kept at 17° C continuously, but flowering-abundancy was the same. Lowering of the temperature in the last period before harvest did not influence shoot growth, but markedly reduced flowering of both spur buds and apical shoot buds.In a second experiment, a night temperature of either 20 or 10° C was applied in 2 successive periods to 3-year-old ‘Cox's Orange Pippin’ trees kept at a day temperature of 20° C throughout. Lowering of the night temperature in the middle of the season reduced flower-bud production, but there was no difference in growth vigour compared with 20° C continuously.It is postulated that temperature affects flowering in two opposite ways, whose relative importance determines the net result.     

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.     

Effect of temperature on bulb growth capacity and sensitivity to summer sprouting in Lilium longiflorum Thunb.

The production of Lilium longiflorum bulbs in The Netherlands, with its cool climate, has been a problem because of unsatisfactory bulb growth and the risk of premature sprouting of the daughter bulbs (summer sprouting). To investigate the possibilities of breeding a type of L. longiflorum that can be grown under cool climatic conditions, a collection of 27 L. longiflorum cultivars from Japan, The Netherlands and the United States was tested, together with two Asiatic hybrids and a L. speciosum cultivar, under low phytotron temperatures (10, 14, 17°C) and in field experiments.‘Mount Everest’, ‘Saeki’, ‘Indian Summer’ and ‘White American’ were among the best L. longiflorum cultivars, with less than 20% summer sprouting and good bulb production. This was in contrast to ‘Hinomoto’, ‘Ace’ and some American introductions, which showed more than 60% summer sprouting and low bulb production. The lower the phytotron temperature, the more summer sprouting occurred. The differences observed between the cultivars in the field experiments were in agreement with those observed in the phytotron. The genetic variation proved large enough to start a breeding program for L. longiflorum adapted to cool climate conditions.