A.R. Rees

The physiology of ornamental bulbous plants

ConclusionIt may be concluded that a great deal of work has been devoted to bulb physiology, and in particular to the temperature-treatment of bulbs in the dormant phase. Bulb growers are heavily indebted to the work carried out by the Dutch at Lisse and Wageningen in the first half of this century for the present success of the bulb industry. Despite these efforts, there are a number of aspects of bulb physiology which have never been adequately explained (the effect of low temperature in promoting rapid growth to flowering is an obvious example) and more work is required on other stages in the bulb life history, especially growth in the field. This aspect of bulb growing has been neglected because very little can be done to ameliorate adverse conditions-largely low temperatures—in the field. There is an urgent need in Britain for an appraisal of how far the Dutch recommendations are applicable to bulbs grown under different climatic and edaphic conditions and whether supplementary or different storage temperature treatments (e.g., those developed for the Southern United States) may be of benefit.In Britain, Dutch-recommended temperatures are generally very successful, but every grower has experienced difficulties due to climate or microclimate during storage treatments interacting with the great sensitivity of bulbs to their environment. The number and variety of these problems form a stimulus for continued physiological work on bulbs.

Growth of the tulip shoot

Abstract Tulip bulbs (cv. ‘Apeldoorn’) were grown under three commercial forcing treatments and in the field in two seasons, and changes in shoot dry weight and height were followed and compared with changes in epidermal cell length. Changes in storage temperature did not always result in changes in dry weight or extension growth of shoots. The final relative growth rates in the field were as high as those of the forced bulbs, and the larger size of the field-grown plants was due to their longer growth period. Stem and leaf extension were almost entirely due to elongation of cells produced early in development, but there were some indications of cell division in field-grown plants. In a late season (flower initiation 2–3 weeks later than normal) cell number appeared to be low. Stems were short because of inadequate cold treatment, except in one case where extra cold resulted in normal stem lengths but with very long cells. We suggest that low cell number in the shoot is associated with late flower initiation, and that this may be due to small apical size. Early forcing of such material is unsuccessful, although growth in the field is satisfactory, because a longer growing season allows further cell division to occur.

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.

Effects of growth-regulating chemicals on two cultivars of Mid-Century Hybrid lily

Abstract The effects on growth and flowering of Mid-Century Hybrid lilies ‘Enchantment’ and ‘Joan Evans’ of soil drench applications of ancymidol at 0, 5, 10 and 15 ppm have been compared with those produced by drenches of chlormequat chloride, chlorphonium chloride and ethephon at 25 000, 1000 and 1000 ppm, respectively. Ancymidol inhibited stem growth more effectively than a 5000-fold greater quantity of chlormequat chloride. Chlorphonium chloride had little dwarfing effect, and ethephon, although producing height reductions similar to those obtained with 5 ppm ancymidol, delayed flowering slightly in both cultivars (significantly in ‘Enchantment’), and adversely affected overall plant appearance. Ancymidol reduced the lateral spread of foliage, increased the proportion of the total stem length bearing dead leaves, did not significantly delay flowering in either cultivar and appeared to favour the initiation and survival of secondary flowers in ‘Enchantment’.

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.

The influence of timing of application and gibberellic acid on the effects of ancymidol on growth and flowering of Mid-Century Hybrid lily cv. Enchantment

The response of Mid-Century Hybrid lily ‘Enchantment’ to ancymidol has been investigated in two experiments. In the first, three dates of application were employed, the earliest at inflorescence initiation, the second and third 10 and 20 days later, respectively. Application (750 μg/plant as a 15 ppm soil drench) on the second date produced the shortest plants, a result attributed to more extensive uptake by a better-developed root system. Plants subjected to treatment on the third date were, by then, too tall for the maximum dwarfing effect to occur. Flower number was unaffected by treatment, but ancymidol delayed anthesis by between 4 and 6 days and promoted earlier senescence of basal leaves. In the second experiment, interactions between gibberellic acid (GA3) and ancymidol were demonstrated. Increasing amounts of GA3 (20, 200 and 2 000 μg/plant as aqueous applications to the shoot tip) progressively counteracted the dwarfing effect of ancymidol (500 μg/plant as a 10 ppm soil drench) and, in the absence of ancymidol, 2 000 μg GA3/plant significantly promoted stem extension. Flower number was slightly decreased by GA3 in the absence of ancymidol. An ancymidol-induced delay in anthesis of almost 5 days was progressively reduced by increasing levels of GA3, which, in the absence of ancymidol, did not significantly influence the time of anthesis. Applied separately, neither ancymidol nor GA3 significantly affected pedicel length of the first flower, but increasing levels of GA3 progressively promoted pedicel elongation in the presence of ancymidol.

An analysis of the growth of forced tulips. 2. Effects of low-temperature treatments during development on plant structure at anthesis

Abstract The effects of different periods of storage at low temperature on some plant parameters were examined at anthesis. The duration of the low-temperature storage affected the time taken for plants to reach anthesis, the stem lengths and shoot dry weights. However, flower size and dry weight scarcely altered with the duration of treatment. Despite large differences in the dry weights of the plant components at anthesis following different periods of low-temperature storage, the ratio of total plant dry weight at anthesis to the initial bulb dry weight at the commencement of treatment remained almost constant. Anthesis occurred in all treatments when the total plant dry weight fell to 70% of the original bulb mass. It is possible to relate flower quality to the fresh to dry weight ratio of the flower.

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.

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.