Search

It is well known that Fusarium oxysporum f. sp. tulipae (Fot), ethylene and jasmonates have a promoting effect on gum induction and its accumulation in tulip (Tulipa gesneriana L.) bulbs. The induction and production of gums are suggested to be regulated by a signal network of jasmonates and ethylene, especially by cross-talk between them. Tulip gums consist of glucuronoarabinoxylan with an average molecular weight of approximately 700 kDa. In this review some biological activity of tulip gums is presented. It is believed that gums have a function in limiting the spread of fungal and bacterial pathogens and insects by isolating the infected tissues. It was found that the addition of tulip gums at a concentration of 5 mg•cm3 to Czapek-Dox-Agar, Malt-Extract-Agar and Potato-Dextrose-Agar greatly stimulated mycelium growth of Fusarium oxysporum f. sp. tulipae and sporulation of the pathogen. Addition of tulip gums to the Czapek-Dox-Broth caused that the pathogen secreted the polysaccharide gum degrading enzymes. In further studies it was found that tulip gums induced by Fusarium oxysporum f. sp. tulipae, ethylene or jasmonates elicited red coloured secondary metabolite(s) in mycelium of the pathogen. The effect of homogenate of different tulip organs (scales, leaves, stem, pistils and roots), applied alone and simultaneously with tulip gums, on red pigment formation by mycelium of F. oxysporum f. sp. tulipae was investigated. It is interesting that a homogenate of tulip scales and pistils almost totally inhibited the formation of the red coloured pigment induced by tulip gums in the mycelium of Fot. It is possible that the polysaccharide of tulip gums, which is glucuronoarabinoxylan, may act as an elicitor that regulates some physiological and biochemical processes connected or responsible for mycelium growth of the Fusarium oxysporum f. sp. tulipae and induction of secondary metabolites by mycelium of the pathogen.

Tulip bulbs (Tulipa gesneriana ‘Apeldoorn’ and ‘Gudoshnik’) with a terminal bud containing a complete flower were treated with 2,3,5-triiodobenzoic acid (TIBA) at 0.2 and 0.5% (w/w in lanolin) on the scale around the basal plate of bulbs and then subjected to the cooled treatment. After different periods of dry-cooling at 5°C, bulbs were grown in a greenhouse under natural light conditions. The application of TIBA to the partially dry-cooled bulbs substantially promoted not only shoot growth but also flowering. The growth- and flowering-promoting effect of TIBA was weaker in the fully cooled than in the partially cooled bulbs. It should be mentioned that TIBA applied to the scale did not stimulate shoot growth and flowering in uncooled tulip bulbs. These results suggest that the application of TIBA to the scale of tulip bulbs partially replaces the cold treatment, or shortens the period of dry-cooled treatment for shoot growth and flowing in tulips bulbs. A possible explanation for TIBA-induced shoot growth and flowering in partially cooled tulip bulbs is proposed on the focus of the balance of endogenous plant hormones.

Genomic in situ hybridization (GISH) was used to understand the process of interspecific tulip hybrid diploid (2n = 2x = 24), triploid (2n = 3x = 36) and tetraploid (2n = 4x = 48) cultivar formation. Simultaneous hybridization of differentially labelled genomic probes enabled chromosomes derived from T. gesneriana and T. fosteriana to be distinguished in all cultivars tested. Diploid cultivar ‘Shirayukihime’ contained one set of chromosomes from T. gesneriana and one set from T. fosteriana. In triploid cultivars ‘Come Back’, ‘Diplomate’, ‘Pink Impression’ and ‘Oxford’, 24 chromosomes were derived from T. gesneriana and 12 chromosomes originated from T. fosteriana. The genome of tetraploid cultivar ‘Ollioules’ comprised 36 chromosomes from T. gesneriana and 12 chromosomes from T. fosteriana. In all tulip hybrids, GISH signals were localized predominately in telomeric/subtelomeric and intercalary regions of T. gesneriana chromosomes, whereas T. fosteriana chromosomes were painted more evenly along the chromosome length. In triploid and tetraploid cultivars, cross-hybridization to putative rRNA gene sites was observed at telomeric and intercalary locations of some chromosomes, although additional experiments are needed to identify what kind of repetitive DNA families are arranged as nested elements interspersed in the tulip genome. INTRODUCTION Tulip is one of the most important ornamental crops. Every year many new cultivars are introduced to the market, some of which have been made by interspecific hybridization between genotypes of cultivated tulips (Tulipa gesneriana) and other Tulipa species (Van Eijk et al., 1991; Van Creij et al., 1997). Crosses between T. gesneriana and T. fosteriana are especially successful (Van Eijk et al., 1991; Van Creij et al., 1997), most of which are triploid (2n=36), whereas a few are diploid (2n=24) and tetraploid (2n=48). Vigorous traits such as large flowers, sturdy stems and large plant size are exhibited primarily by the triploid forms. Because of their distinct traits, these vigorous forms were given a classification of their own in the tulip classification list (Killingback, 1990), and are referred to as Darwin Hybrid Tulips. Because most of the diploid forms obtained from crosses between T. gesneriana and T. fosteriana do not show vigorous growth, they are classified in other horicultural groups; for example, ‘Shirayukihime’, is registered under Single Late Tulips. From these crosses, over 50 cultivars of Darwin Hybrid Tulips have been developed so far; most are triploid, one cultivar ‘Spring Song’ is a diploid, and a few are tetraploids (e.g., cultivar ‘Ollioules’ (Van Scheepen, 1996; Okazaki et al., 2005)). The triploid Darwin Hybrid Tulips have spontaneously resulted from unreduced gametes. By studying karyotype in tulips, Marasek et al. (2006) demonstrated that the Darwin Hybrid Tulips tested have two copies of the T. gesneriana genome and one copy of the T. fosteriana genome, indicating that T. gesneriana has supplied the diploid gamete. However, identification of the genome constitution of Darwin Hybrid Tulips using GISH has thus far been limited to the triploid cultivar ‘Yellow Dover’. For most Darwin Hybrid Tulip cultivars, little is known about their genome consitution, especially for the tetraploid form. In addition, it is unknown whether homologous recombination has occurred in polyploid genotypes between T. gesneriana and T. fosteriana chromosomes. 133 Proc. XX Intl. Eucarpia Symp. (Sect. Ornamentals) on Breeding for Beauty (Vol II) Eds. A. Mercuri and T. Schiva Acta Hort. 743, ISHS 2007 The objective of the present study was to use GISH to determine the genome composition in diploid (2n = 2x = 24), triploid (2n = 3x = 36) and tetraploid (2n = 4x = 48) tulip cultivars, which were obtained from interspecific crosses between T. gesneriana and T. fosteriana. MATERIALS AND METHODS Plant Materials The following tulip genotypes were used in this study: diploid cultivar ‘Shirayukihime’ (2n = 2x = 24), which was obtained from the interspecific hybridization between T. gesneriana and T. fosteriana (Kimura, 2002) and belongs to the classification group Single Late Tulips; triploid cultivars ‘Come Back’, ‘Diplomate’, ‘Pink Impression’ and ‘Oxford’ (2n = 3x = 36) (Darwin Hybrid Tulips); and tetraploid cultivar ‘Ollioules’ (Darwin Hybrid Tulips) (2n = 4x = 48). Cultivars were classified according to Van Scheepen (1996). Bulbs were obtained from the Toyama Bulb Growers Association, Japan. Chromosome Preparation Root tips were pre-treated with 0.05% colchicine at 18°C for 2.5 h and fixed in 3:1 (v/v) absolute ethanol:glacial acetic acid and stored at −20C. Root tips were washed in enzyme buffer (0.01 M sodium citrate, pH 4.8) for 20 min prior to digestion in an enzyme mixture containing 2% (w/v) cellulase Onozuka-RS (Yakult Honsha Co., LTD. Japan) and 1% (w/v) pectolyase Y-23 (Kyowa Chemical Products Co., LTD. Japan) for 2.5 h at 37oC. Meristems were squashed in a drop of 45% acetic acid, cover slips were removed by freezing on dry ice and preparations were dehydrated in absolute ethanol and air-dried. DNA Probes and In Situ Hybridization Total genomic DNA from ‘Red Emperor’ (T. fosteriana; 2n = 2x = 24) and ‘Queen of Night’ (T. gesneriana; 2n = 2x = 24) was extracted from the leaves using the standard cetyltrimethylammonium bromide (CTAB) method (Murray and Thompson, 1980). DNA was sonicated to yield 1–10-kb fragments and labelled by nick translation with either tetramethyl-rhodamine-5-dUTP (T. fosteriana) or digoxigenin-11-dUTP (T. gesneriana) (Roche). Autoclaved T. sacstatila DNA (100–500 bp) was used as blocking DNA in 30–75× excess of the probes. The method for in situ hybridization and probe detection followed Hasterok et al. (2001) with minor modifications. Slides were pre-treated with RNase A (100 μg/ml) for 1 h at 37oC, then washed in 2× SSC, post-fixed in 1% formaldehyde in PBS buffer for 10 min, washed again in 2× SSC and dehydrated in absolute ethanol. The hybridization mixture consisted of 50% deionized formamide, 10% dextran sulphate, 2× SSC, 1% SDS and probe DNA (200 ng of each per slide). The hybridization mixture was denatured at 75oC for 10 min and chilled on ice. Chromosome preparations and pre-denatured probes were denatured at 70oC for 10 min. Hybridization was carried out overnight in a humid chamber at 37oC followed by stringent washes in 2× SSC for 15 min at room temperature and in 0.1× SSC for 30 min at 42oC. The digoxigenated probe was immunodetected using the standard protocol with FITC-conjugated anti-digoxigenin (Roche). The chromosomes were counterstained with 1 μg/ml 4,6-diamidino-2-phenylindole (DAPI, Sigma) in Vectashield (Vector Laboratories). Images of fluorescently stained chromosomes were acquired using a digital camera attached to a microscope (BX51N, Olympus, Japan) with an appropriate filter and then processed using software (DP Manager, Olympus, Japan). RESULTS AND DISCUSSION Distribution of GISH Signals Simultaneous application of differentially labelled ‘Queen of Night’ (T. gesneriana) (green) and ‘Red Emperor’ (T. fosteriana) (red) total genomic DNA probes

Flowering was slightly accelerated when iris was grown with 10.7:3.9 meq/L N:K and flowering percentage and vase life were increased when it was grown at a higher nitrogen level (17.9:3.9 meq/L N:K). CO2 concentration increased as the postharvest storage period was prolonged. Flowering of tulip was promoted by 14.3:3.9 meq/L N:K and internode diameter was significantly increased. Flowering of tulip, cultured with 10.7:3.9 meq/L N:K, 12.1:5.1 meq/L N:K and 14.3:3.9 meq/L N:K treatments, was somewhat delayed by postharvest sealing treatment, and quality was also maintained highly. Growth and flowering of lily was not significantly different between treatments. Vase life of the flowers 1-3 was increased (less than 1 day) by the highest nitrogen treatment, 17.9:3.9 meq/L N:K. In case of respiration rate in lily, cultured with 10.7:3.9 meq/L N:K, postharvest lily stored at 3°C was lower than 5°C. INTRODUCTION The cut iris, tulip, and lily are typical export flower crops in Korea. For plants, absorption of nutrient solution is an important factor during growth. Water and minerals are not taken up from a nutrient solution in the same proportion in which the components are present. The rate of absorption depends upon the plant, the climatic and environmental conditions such as light intensity and duration, temperature, and humidity, as well as the type of culture and the stage of development of the crop (Shim et al., 2001). The form of the nutrient is also important, for example, ammonium nitrogen has positive effects on the growth and development of carnations, including promotion of flowering time and increasing flowering percentage (Ishida and Masui, 1976). Modified atmosphere packaging (MAP) is widely used for both whole and fresh cut products to extend storability and shelf-life during the marketing period (Kader, 1986; Kim, 1998; Watada, 1997; Watada and Qi, 1999). For roses, with time, CO2 accumulates inside the bag, while the relative oxygen concentration is depleted, with the result that the quality of the flowers is improved (Salunkhe et al., 1990). Therefore, this experiment was performed to determine the effects of nutrient solution management and methods of storage and distribution on post-harvest quality in iris, tulip and lily. MATERIALS AND METHODS Effects of Culture Temperature and Nutrient Solution Management on Postharvest Quality in Cut Iris, Tulip and Lily This experiment was done in a greenhouse with a hydroponic system. Air temperature of the greenhouse was at 26/18°C (max./min.). Bulbs of Iris hollandica ‘Blue Magic’, 9-10 cm in circumference, were stored at 5°C for 8 weeks until planting. Bulbs of Tulipa gesneriana ‘Hollandia’, 10-12 cm in circumference, were stored at 5°C for 9 weeks until planting. Bulbs of Lilium ‘Siberia’, 13-15 cm in circumference, were stored at 5°C for 12 weeks until planting. Water was given during the first one week after planting, then nutrient solutions of four nitrogen and potassium levels were used. The Proc. IX Intl. Symp. on Flower Bulbs Eds.: H. Okubo, W.B. Miller and G.A. Chastagner Acta Hort. 673, ISHS 2005 514 nutrient solutions were as follows (all given as N:K, meq/L of each): 10.7:3.9, 12.1:5.1, 14.3:3.9, and 17.9:3.9. The basic nutrient solution also contained macro elements (P:Ca:Mg = 3.0:8.4:4.0 meq/L) and micro elements (Fe:3.0, Mn:0.5, B:0.5, Zn:0.25, Cu:0.03, Mo:0.05 ppm). The nutrient solution was given once per week during the experiment. The pH was maintained 6.5-6.7 and EC was 1.3-1.4 mmho/cm. Plant height, days to flowering, flowering rate, longevity, and diameter of the internode were measured. Effects of Storage and Distribution Conditions on the Postharvest Physiology of Iris, Tulip and Lily Grown in Different Nutrient Conditions Effect of modified atmospheres (MA) on flower longevity and possible interaction with nutrient solution composition was studied. Cut iris was stored at 0°C for pre-cooling after harvest. After pre-cooling, one cut iris was placed in a 1L sealed cylinder, and then, two kinds of gas (MAI: CO2 50% + O2 50%, MAII: CO2 5% + O2 3%) were introduced into the cylinder (15 ml/min for 1 minute). Also, cut iris sealed into cylinders without introduction of gas (MAIII) was dipped in distilled water. The control was dipping in distilled water with cut iris in open air. All treatments were stored at 4°C for 4 days, then the flowering degree and quality and CO2 concentration were measured. Cut tulip was treated with the two gasses, as described above. All treatments were stored at 4°C for 4 days, then the flower developmental index was measured. Flower development was evaluated visually using a scale (1 = green flower bud, 5 = full flowering). The flowering index was determined by multiplying the number of stems at each index value then dividing by the total number of stems. Cut lilies grown with the different nutrient solutions were stored at two temperatures (3 or 5°C) for 4 days, and then, stored at 6°C in a dry or wet condition to simulate transport. Respiration rate was measured every 4 days. Respiration rate was measured by gas production that was calculated from an analysis of 1 ml samples of the head space gas accumulated in 1.5 L chamber in which a cut lily was placed. Three replications were used in each treatment. Gas was analyzed by gas chromatography (GC) of which the operating condition is shown in Table 1. RESULTS AND DISCUSSION Effects of Culture Temperature and Nutrient Solution Management on Postharvest Quality in Cut Iris, Tulip and Lily Flowering was accelerated when iris was grown with 10.7:3.9 meq/L N:K as compared with other treatments (Table 2). The flowering percentage was increased when iris was grown with the highest nitrogen level (17.9:3.9 meq/L N:K) treatment. Also flower development was slightly increased by the highest nitrogen treatment. Nitrogen had no effect on plant height, leaf length and width, stem diameter, and degree of senescence and flower longevity. Plant height was decreased and plants flowered slightly faster when tulip was grown with 14.3 meq/L nitrogen as compared with other treatments (Table 3). Growth and flowering of lily were not significantly different between treatments but plant height was slightly decreased when lily was grown at the highest nitrogen level (Table 4). Leaf number and flower width were slightly increased by the 14.3:3.9 meq/L N:K treatment, but these differences are probably of no commercial significance. Vase life of flowers 1 to 3 was prolonged by less than 1 day by the highest nitrogen treatment. Nitrogen had no effect on lily stem diameter, days to flowering, leaf length and width, and flower length and number. Effects of Storage and Distribution Conditions on the Postharvest Physiology of Iris, Tulip and Lily Grown in Different Nutrient Conditions For iris, CO2 concentration increased as the postharvest storage period was prolonged (Fig. 1). Especially, CO2 concentration showed the lowest degree at MAIII treatment as compared with other treatments, and we could find that flowering was

Ethylene evolution is a well-known consequence of Fusarium infection of tulip (Tulipa gesneriana) bulbs, yet little is known about the bulb-pathogen interactions involved in the induction or the time course of ethylene production in the infected bulb. Bulbs of 36 tulip cultivars were wounded, inoculated with a liquid Fusarium suspension (isolated from infected bulbs, and grown on agar plates) and held at 21°C. Control bulbs were wounded, but not inoculated. Ethylene production was monitored by headspace accumulation and gas chromatography. The results indicated that ethylene could increase rapidly after a lag phase of at least 8 days after inoculation, but there was a great variability in ethylene production among cultivars. Of the cultivars tested, the highest ethylene producer was ‘Furand’, which evolved more than 340 µl/kg fwt wt/h (ca. 250 µl/bulb/day) on the 12 th day after infection. By 19 days, inoculated ‘Furand’ and ‘Nashville’ produced ethylene at ca. 800 µl/bulb/day. Approximately 40% of the cultivars produced ethylene at rates greater than 150 µl/bulb/day, and only 11% of them produced less than 5 µl/bulb/day. These results suggest high-ethylene producing tulips should be stored separately from other cultivars, or that increased ventilation should be maintained during storage or transportation. Knowledge of cultivar variation might also be useful in breeding programs.

We conducted biochemical and molecular analysis of tulip amylase. Enzyme extract was obtained from the scales of tulip bulbs after cold treatment for forcing cultivation, and some characteristics of the amylase were investigated. The amylase activity was measured by iodine-starch method. The degradation of soluble starch produced a series of maltooligosaccharides with different sizes. This indicates that the amylase in tulip bulb scale is endotype α -amylase. The optimum pH for amylase activity was about 5.6. The enzyme activity was stable at neutral and alkaline pH (pH 5-10) at 4°C for 24h, but the activity remarkably decreased in acidic pH (pH

Bulbs of Tulipa gesneriana ‘Queen of Night’ at stage G3 were treated with low temperature at 4°C or 8°C for 0 to 10 weeks and then grown under forcing conditions in a greenhouse. The developmental process of microspores with different low temperature treatments follows a similar developmental pattern, irrespective of the duration of low temperature. Pollen remained at the uninucleate stage for a long time after planting, then rapidly developed into the binuclear stage about one week before anthesis and then into mature pollen. Generally, the days from planting to anthesis decreased, while the percentage of stainable pollen and the floral stalk length increased with increasing chilling duration. However, the flowering percentage declined in the bulbs treated at 4°C for 8 and 10 weeks. Stainable pollen in all treatments ranged 70-90% at anthesis. Treatment of the bulbs with a higher stainable pollen percentage at the time of anthesis resulted in longer floral stalks too. This positive correlation suggests that the elongation of floral stalk induced by chilling probably affects the development of pollen and vice versa.

The propagation of tulip (Tulipa gesneriana L.) in vitro fully depends on vegetative bulb formation. To determine the internal and external factors influencing bulb development, the in vitro shoots of two cultivars of tulip were used for experiments: 'Blue Parrot' - with high rate of shoot multiplication but difficult-to-form bulbs, and 'Prominence' - well multiplying and easily forming bulbs. Effects of exogenous abscisic acid (ABA), methyl jasmonate (MeJA) and gibberellin (GA 3 ) as well as environmental factors (light, darkness and cooling period) and the kind of gelling agent on bulb formation were studied. Contents of endogenous plant hormones for in vitro shoots were determined by ELISA. The content of ABA and trans-zeatin riboside (t-ZR) in 'Blue Parrot' was significantly higher than in the shoots of 'Prominence'. After cooling (4°C), the content of endogenous ABA in shoots of 'Blue Parrot' decreased, but it was still 70% higher than in the 'Prominence' shoots before the low temperature treatment. The level of endogenous cytokinins (t-ZR and IPA - isopentenyladenosine) in 'Blue Parrot' significantly increased after cooling. Bulb formation of this cultivar was negatively influenced by ABA application. The results suggest that the poor capacity for bulbing observed in 'Blue Parrot' may result from high concentration of endogenous ABA and t-ZR in the shoots of this cultivar. A significant improvement of bulb development was obtained by extending the cooling period up to 14 weeks, as well as by application of MeJA and activated charcoal into the medium.

We investigated the application of the nutrient film technique (NFT) culture to tulip forcing to improve water circulation and rooting in tulip hydroponics. After precooling at 15C for 2 or 3 weeks, dry bulbs of ‘Gander’ and ‘Ben van Zanten’ tulips were chilled at 5C for 7 or 8 weeks. After chilling treatment, bulbs were planted using the NFT system and a plug tray. Tap water, controlled at 13C, 18C, or 23C, was supplied for 30 minutes every 3 hours without adding of fertilizer. Shoot growth increased with increasing water temperature. No stem topple or other growth disorders and flower abortions were observed. The number of days to flowering increased with decreasing water temperature. The cut flower quality improved at 13C water temperature. We conclude that NFT culture could be a good choice for tulip forcing by hydroponics. INTRODUCTION Tulip (Tulipa gesneriana L.) is considered to be suitable for forcing culture by hydroponics because 1) the plant size is relatively small, 2) the bulb accumulates a considerable amount of nutrition and grows rapidly, 3) chilling treatment can be used for to dry bulbs. The recent technique of tulip deep flow hydroponics using a special hydroponic tray (De Hertogh 1996) has the disadvantages of the occurrence of root rot caused by the restriction of water circulation or supply of oxygen, of the unstable way of fixing the bulbs on the tray, and of calcium deficiency symptoms caused by inadequate combination of nutrients and high root zone temperature (Klougart 1980; Nelson and Niedziela Jr. 1998a, 1998b) or the restricted root zone. We investigated the application of the nutrient film technique (NFT) to tulip forcing because it may improve the culture condition in the deep flow hydroponics. Figure 1 shows the NFT system we used was specially designed for a new nursery system of paddy rice seedlings called ‘Long Mat’ by Tasaka (1999). It was distinguished from the ordinary NFT system by only the length of the channel and the lack of root-covering materials. MATERIALS AND METHODS Bulbs of ‘Gander’ and ‘Ben van Zanten’ (grown in Japan, 11-12 cm in circumference) were obtained in early August and were kept at 25C. From August 16, dry bulbs were precooled at 15C for 2 or 3 weeks and then were chilled at 5C for 7 or 8 weeks. After the chilling treatment, the tunic was removed from the basal plate. Then, the bulbs were planted on the ‘Long Mat’ NFT system in a glasshouse using a plug tray for the vegetable seedling raising, which was used due to fix the bulbs and support the plants; each bulb was crammed firmly into a cell of a 50-cell plug tray (28 X 55 cm). In the channels of ‘Long Mat’, a polycarbonate corrugated sheet (Takiron Co. Ltd., Japan) was laid to improve the drainage (Figure 2). Tap water, controlled at 13C, 18C, or 23C, was supplied for 30 minutes every 3 hours without adding of fertilizer (the tap water contained 1 ppm NO3-N). The planting density was 50 bulbs per tray. In the glasshouse plants were grown at Proc. 8th Int. Symp. on Flowerbulbs Eds. G. Littlejohn et al. Acta Hort. 570, ISHS 2002 424 a minimum air temperature of 8C under 40% shading. At the flowering stage, flowers were cut, and the length of stalk and weight of cut flowers, and the length of the perianth, were measured. RESULTS AND DISCUSSION Although the basal plate of the bulb was not immersed in water because the highest water level was approximately 1cm below the rooting zone of the bulb, the root started rooting and elongated smoothly. Shoot growth until 2 weeks after the planting was retarded in all treatments (Figure 3). In these 2 weeks, plants seemed to develop the root system. The roots developed along the groove of the corrugated sheet and supported the plants firmly. The roots seemed healthy because rot or discoloration of roots was hardly observed. The shoot grew normally without adding special fertilizer. Shoot growth was vigorous from 3 weeks after planting, and increased with increasing water temperature. In all treatments of both cultivars, all plants flowered normally; abortions were not observed. Topple or other growth disorders due to calcium deficiency (Klougart 1980; Nelson and Niedziela Jr. 1998a, 1998b) were not also observed. The number of days to flowering increased with decreasing water temperature in all treatments (Table 1). At 23C water temperature, both cultivars flowered at about 50 days after planting, irrespective of the duration of the chilling treatment. In ‘Gander’, the cut flower quality (the stalk length and weight of cut flower) improved in plants at 13C compared with plants at higher temperatures, except the treatment of 3 weeks at 15C followed by 8 weeks chilling at 5C. In ‘Ben van Zanten’, water temperature affected the stalk length of cut flowers similar to ‘Gander’. We conclude that the number of days to anthesis increased, but the cut flower quality improved more in the lower root temperature treatment. Further investigation is necessary on the alternation of the water temperature according to the growth stage, because the suitable temperature is different for root growth and for shoot growth (Le Nard and De Hertogh 1993). In conclusion, tulip forcing by NFT is a practical and laborsaving culture technique, and it improved some weak points of the deep flow culture. We used no additional nutrients in this experiment, but if a solution containing appropriate mineral nutrients is supplied, growth will increase and the cut flower quality will improve. NFT culture may take more days for plants to flower than rooting room bulb forcing, but the growing period is variable to some extent with changing water temperature. ACKNOWLEDGEMENTS We wish to thank Dr. T. Motozu of Ibaraki Horticulture Research Institute for his critical reading of the manuscript and Dr. O. Urashima of Toyama Vegetable & Ornamental Crops Experiment Station for his helpful comments on the experiments. Literature cited De Hertogh, A.A. 1996. Holland bulb forcer ’s guide, 5th edition. The International Flower-bulb Center, The Netherlands. Klougart, A. 1980. Calcium uptake of tulips during forcing. Acta Hort. 109:89-95. Le Nard, M. and De Hertogh, A.A. 1993. Tulipa. In: M. Le Nard and A.A. De Hertogh, eds. The physiology of flower bulbs. pp.617-682, Elsevier, The Netherlands. Nelson, P.V. and Niedziela Jr., C.E. 1998a. Effects of calcium source and temperature regime on calcium deficiency during hydroponic forcing of tulip. Scientia Hort. 73:137-150. Nelson, P.V. and Niedziela Jr., C.E. 1998b. Effects of ancymidol in combination with temperature regime, calcium nitrate, and cultivar selection on calcium deficiency symptoms during hydroponic forcing of tulip. Scientia Hort. 74:207-218. Tasaka, K. 1999. Raising and transplanting technology for long mat with hydroponically grown rice seedlings. Japan Agriculture Research Quarterly 33:31-37.

The maximum ethylene level that can be permitted in storage rooms, without causing damage to tulip bulbs, is not exactly known. Therefore, a zero-tolerance for the presence of ethylene during storage of tulip bulbs is common practice. This results in excessive ventilation and coherent large energy costs. It is questioned whether this is always necessary. In different phases of the storage period the critical levels of ethylene were determined. Bulbs of eight economically important cultivars (‘Apeldoorn’, ‘Christmas Marvel’, ‘Leen van der Mark’, ‘Monte Carlo’, ‘Negrita’, ‘Prominence’, ‘White Dream’ and ‘Yokohama’) were exposed to various ethylene levels. In the first experiment bulbs were exposed to ethylene for two days shortly after harvest. Only in the cultivar ‘Apeldoorn’ this resulted in gummosis. In two subsequent experiments later during storage, bulbs were exposed to various ethylene levels during five weeks. Bulbs were investigated on visible internal damage, flower quality and bulb production. Damage depended on applied ethylene level, cultivar and period of storage. Research will be continued to define tolerable ethylene levels, taking into account the cultivar and the developmental stage of the bulb.

International audience

Large numbers of adventitious shoots have been induced to form in vitro on floral stem sections of Tulipa gesneriana L. cultivar Merry Widow. In comparison with explants of scale and axillary bud, floral stem tissues showed the greatest potential for shoot production. A modified Murashige & Skoog medium contained inorganic salts and vitamins at full strength and supplemented with benzylamino-purine and napthalene-acetic acid at 1 mg‾1 induced shoots on 70%-90% of floral stem explants. The stage of development of the bulb was found to be an important factor in determining the ability of explants to regenerate shoots. The shoot producing potential of floral stem tissues was greatest during the 'dormant' phase of the bulbs, but the ability to produce shoots was lost once rapid extension growth and greening of the floral stem had commenced. Morphogenesis in vitro was found to be influenced by the origin of explants from within the floral stem. A study of endogenous plant growth regulators was made within the floral stem in order to elucidate their role in the organogenetic processes occurring in vitro. A study of histological and morphological development in vitro showed that the shoot-like structures arise from the epidermal cell layer and have the potential to form whole plants.