Gordon R. Hanks

Twin-scale propagation of narcissus: A review

Abstract Natural rates of multiplication of many important bulbous ornamentals are low because they produce few daughter bulbs, and various techniques have been developed to overcome this deficiency. In narcissus the most effective method (other than shoot proliferation by tissue culture) is twin-scaling: parent bulbs are cut into longitudinal segments which are then separated into adjacent scale-pairs joined by a portion of the basal plate (twin-scales). On incubating these propagules in moist vermiculite (or planting in compost), bulbils develop at the edge of the basal plate. This review begins by describing the background to twin-scaling work and the general characteristics of bulbil growth. Factors affecting twin-scale propagation are then considered in detail: date of twin-scaling, twin-scale size and cutting rate, scale age, disinfection and other factors relating to incubation technique, temperature and duration of incubation, pre-scaling and post-incubation temperatures, varietal and clonal effects, and first-year dormancy. The twin-scaling technique has potential value in current programmes to multiply rapidly virus-free narcissus bulbs for the replacement of infected commercial stocks. The review ends by discussing the multiplication rates which can be expected, and examines the potential roles of twin-scaling and tissue culture in current multiplication programmes.

Factors affecting the response of tulips to gibberellin

Abstract Gibberellic acid (GA 3 ) 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 GA 3 treatments) were studied. Experiments confirmed the previously recorded effects of gibberellins in tulips: GA 3 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, GA 3 reduced the glasshouse period by 15–25% and increased flower length, compared to controls, irrespective of storage temperature. Stem length was also reduced by GA 3 , this effect being greater following a storage temperature of 5°C or lower. When GA 3 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 GA 3 than were pre-cooling applications. In partly cooled bulbs (but not fully cooled ones), the GA 3 -induced earliness of flowering was about doubled when GA 3 injections were given repeatedly at 2-week intervals throughout storage. The responses to GA 3 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.

Growth Substances of Tulip: The Activity of Gibberellin-like Substances in Field-grown Tulips from Planting until Flowering

Summary The activity of gibberellin-like substances (GLS) was determined, using a lettuce hypocotyl bioassay, for the various bulb and plant components of tulip cv. «Apeldoorn» growing in the field in southern England. Plants were sampled at intervals from October (planting time) until the following April (flowering time). Two peaks of GLS activity were found over the course of the samples. The first of these occurred in December or early-January in most components, prior to the satisfaction of the cold requirement. In the acidic fraction there was a peak of GLS activity in the December sample in leaf and daughter bulb (DB) extracts, and in the early-January sample in extracts of the stem and mother bulb scale components; high activity was also found in the young flowers sampled in October and in the basal plate (BP) region containing actively growing root initials sampled on the same date. In the basic fraction, the peak occurred in the December samples of all components (except the outer fleshy bulb scales) preceding the main peak in the acidic fraction. In the bound fraction the peak occurred in December in the flower extracts and in early-January in root, BP, inner scale, leaf and stem extracts, but was absent in extracts of the other components. During this time, the GLS activity of the acidic, basic and bound fractions of the whole bulb increased from 83, 1 and less than 1 to 1308, 431 and 130 ng/bulb, respectively. The second peak occurred around rapid shoot extension and flower maturation (February to April samples), but there was less consistency in its date in the various plant components.

Response of potted tulips to new and established growth-retarding chemicals

Abstract A range of growth-retarding chemicals was evaluated for their potential in the production of compact pot-grown tulips: ancymidol, piproctanyl bromide (Alden), dikegulac-sodium (Atrinal), a phenyl tetrazole compound (coded PP528), 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293), chlorphonium chloride (Phosfon), 2-chloroethylphosphonic acid (Ethrel), and 5 morphactins. All chemicals were applied as single soil drenches 1–2 days after transferring plants to the glasshouse. Mid- and late-season forced bulbs of cultivars ‘Apeldoorn’, ‘Paul Richter’ and ‘Rose Copland’ were used. Piproctanyl bromide and chlorphonium chloride were ineffective, the former causing some stimulation of top internode extension. Ethrel at high concentrations gave a slight reduction in first internode length only, associated with a degree of flower-bud blasting. Dikegulac-sodium gave some reduction in stem and petal length, depending on cultivar. PP528 induced flower-bud blasting, adverse changes in flower colour and reduced petal length at concentrations which effectively shortened stems. Morphactins were toxic or caused flower-bud blasting and other floral abnormalities at high concentrations; at lower doses most morphactins reduced first internode length, while some increased length of the upper internodes, inducing nastic curvature and occasionally altering flower shape. Most effective height control was achieved with ancymidol and UBI-P293, the latter being the more active (at the concentrations tested); flower quality was good. In one experiment only, ancymidol slightly delayed flowering. High concentrations of UBI-P293 gave rise to some flower-bud blasting, especially in ‘Rose Copland’ which showed other adverse side-effects such as decreased length and longevity of the flowers, not only with UBI-P293 but also with higher doses of some other retardants.

Gibberellic acid soak treatments for fully-cooled tulips

Abstract 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.

The response of partly cooled tulips to vacuum infiltration with gibberellins

Abstract Partly cooled (5°C) tulip ‘Apeldoorn’ were treated with gibberellins GA 3 and GA 4 + 7 by vacuum 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 GA 3 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 GA 3 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 GA 3 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 GA 3 concentration reduced both glasshouse period and stem length, with no effect of duration of treatment; GA 3 concentration was the only factor affecting flower length, which was increased. Following 8 weeks cold storage, increasing GA 3 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 weeks 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 GA 3 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 GA 3 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 GA 3 (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 GA 3 was less marked using vacuum infiltration.

Growth regulator treatments to improve the yield of twin-scaled narcissus

Abstract Twin-scaling is a method for the rapid propagation of valuable stocks of bulbous ornamentals. Bulbil production from twin-scales cut from narcissus bulbs was investigated by incorporating plant growth regulators into the vermiculite in which the twin-scales were incubated. Gibberellic acid (1–100 p.p.m.) reduced the number and weight of bulbils produced. Abscisic acid (1–100 p.p.m.), indol-3-ylacetic acid (1–10 p.p.m.) and kinetin (1–100 p.p.m.) increased the weight of bulbils produced by stimulating sprouting of the bulbils, some of which normally remain dormant in their first year.

The response of 9°C-tulips to gibberellins

Abstract In direct-forced (5°C) tulips, gibberellin (GA) application results in earlier anthesis, shorter stem length, and reduced floral bud blasting. Studies with GA were extended to tulips forced following traditional (9°C-cooling) methods. Except in non-cooled bulbs, where anthesis was greatly delayed, GA injections advanced the anthesis date. GA 4+7 was more effective than GA 3 , especially in ‘Rose Copland’ which was less responsive than ‘Apeldoorn’. A study of the effect of time of GA injection revealed that application 4 weeks after the beginning of cold storage was most effective. However, the date of injection of GA had little effect on internode or flower length; GA increased flower and first internode length, but reduced overall stem length at anthesis. GA appeared to have potential for producing short pot-grown tulips with a reduced growing period in the glasshouse.

An evaluation of new growth retardants on Mid-Century Hybrid lilies

Abstract The new growth retardants piproctanyl bromide (Alden or Stemtrol), dikegulac-sodium (Atrinal), PP 528 (a phenyl tetrazole compound) and 2,3-dihydro-5,6-diphenyl-1,4-oxathiin (coded UBI-P293) were compared with the established compounds chlormequat chloride (Cycocel), ancymidol (A-Rest or Reducymol) and chlorphonium chloride (Phosfon), for their ability to dwarf Mid-Century Hybrid lily cultivars ‘Enchantment’ and ‘Joan Evans’. Single compost drenches were given 2–3 weeks after transferring plants to the glasshouse. Piproctanyl bromide at high concentrations (2000 mg a.i. per plant) produced some dwarfing, as did chlorphonium chloride (at 250 mg a.i. per plant). Chlormequat chloride produced a similar response at 1250 mg a.i. per plant, but on a concentration basis ancymidol was by far the most active compound (only 0.25–0.50 mg a.i. per plant was required). Plant and flower quality was generally good with these 3 chemicals. Dikegulac-sodium reduced stem length but prevented the development of flower buds and the plants senesced. PP 528 also restricted stem extension but plant quality was unsatisfactory; increasing concentrations led to smaller florets, weaker stems and drooping leaves. UBI-P293 produced as great a reduction in stem length as did ancymidol, and 100 mg a.i. per plant was as active as 500 mg. However, as the concentration was raised there was a decrease in floret size and number.

Factors affecting twin-scale propagation of narcissus

Abstract The effects of several factors on bulbil yields obtained by twin-scaling were examined in 4 narcissus cultivars (representing poeticus, trumpet and large-cup types). Bulbils were initiated on twin-scales prepared at any time of year, but grew satisfactorily only if twin-scaling was carried out between June and September. Large twin-scales initiated more bulbils, but smaller twin-scales were also effective propagules and gave high rates of multiplication and bulbils with high relative growth rates. Twin-scales cut from the outer-most scales initiated most bulbils, but more of those bulbils produced from the more central scales were recovered after 1 year; those from intermediate scales produced most and heaviest bulbils after 1 year. Partial loss of the basal plate had no effect on bulbil initiation. Optimum bulbil initiation, emergence and first-year recovery rates occurred following incubation at 15 or 20°C; at 25°C these responses were cultivar-dependent. Bulbil yield after 1 year was greater following incubation for 16 weeks compared with 12 weeks. There was little effect on bulbil yield of cold (9°C) or warm (35°C) treatments of the parent bulbs prior to twin-scaling, except for a marked reduction in the numbers of bulbils initiated when the warm treatment immediately preceded twin-scaling. When the propagules were grown on in a frost-free greenhouse (minimum, 5°C) bulbil yields were higher than from those grown either in a warm glasshouse (minimum, 18°C) or in the open; an initial cold period (5°C) given before the propagules were placed in the frost-free house also reduced yield.