The Use of 1-MCP as an Inhibitor of Ethylene Action in Tulip Bulbs under Laboratory and Practical Conditions

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1 The Use of 1-MCP as an Inhibitor of Ethylene Action in Tulip Bulbs under Laboratory and Practical Conditions H. Gude and M. Dijkema Applied Plant Research (PPO), Flowerbulbs P.O. Box AB Lisse The Netherlands Keywords: tulip bulbs, ethylene, 1-methylcyclopropene, 1-MCP, flower abortion, gummosis, bulb splitting Abstract Fusarium infected tulip bulbs produce large amounts of ethylene. During storage and shipping this ethylene causes severe damage in tulip bulbs: an increase in respiration, gummosis, flower abortion (saleable sizes) and excessive splitting (planting stock). The gas 1-methylcyclopropene (1-MCP) is an effective inhibitor of ethylene action in plants by binding to the ethylene receptor. The efficacy of 1-MCP in preventing ethylene effects in tulip bulbs was tested under laboratory and practical conditions. In all experiments, both on a laboratory scale and on a practical scale, the bulbs were fully protected from ethylene by treating them every 12 days for 24 h with.2 ppm 1-MCP. INTRODUCTION Ethylene produced by Fusarium infected tulip bulbs has many harmful effects on healthy bulbs stored in the same storage room or sea container. Well-known short term effects (1 or 2 days) are gummosis or an increase in respiration. Long term effects (3 to 8 months) are excessive splitting in planting stock and flower abortion, multiple shoots and poor rooting in saleable sizes (Kamerbeek and de Munk, 1976). Since it is impossible to remove all Fusarium infected bulbs, the only tool for growers, forcers and exporters to prevent ethylene problems is massive ventilation. In spite of this ventilation, which costs enormous amounts of energy, severe losses can occur during bulb storage and shipping. The gaseous 1-methylcyclopropene (1-MCP) is a powerful inhibitor of ethylene action in plants (Sisler et al., 1996). De Wild et al. (22) showed that the ethylene-induced increase in respiration in tulip bulbs could be prevented by 1-MCP. In this study the efficacy of 1-MCP as an inhibitor of ethylene-induced gummosis, splitting and flower abortion in tulip bulbs was investigated both under laboratory and practical conditions. MATERIALS AND METHODS Tulip bulbs were obtained from growers in July and stored at 2 C until the start of the experiments. In one experiment the duration of the 1-MCP effect was studied by treating bulbs of the cv. Apeldoorn, size 11/12 with.2 ppm 1-MCP for 24 h in a gas-tight tank. A control group was not treated with 1-MCP. Both treated and untreated bulbs were exposed to 6 ppm ethylene for 24 h 3, 6, 9, 12, 15, 2 and 25 days after the 1-MCP treatment. The percentage of bulbs showing gummosis was determined 3 days after the ethylene treatment. In another experiment the effects of 1-MCP on ethylene-induced splitting of planting stock were studied. Planting stock of the cultivars Apeldoorn (size 9/1), Christmas Marvel (size 9/1), Kees Nelis (size 8/1) and Monte Carlo (size 9/1) was stored in a storage room at 2 C from September 15 till November 21. The bulbs were subjected to the following treatments: - no 1-MCP, no ethylene continuously ( Air control) - exposure to 15 ppm ethylene for 24 h every 7 days in a gas-tight tank - exposure to 15 ppm ethylene for 24 h every 7 days and to.2 ppm 1-MCP every 12 days Proc. IX th Intl. Symp. on Flower Bulbs Eds.: H. Okubo, W.B. Miller and G.A. Chastagner Acta Hort. 673, ISHS

2 (in gas-tight tanks). The bulbs were planted in the field by the end of November and harvested in July the next year. The harvested bulbs were dried, cleaned and graded and the numbers and weight of the different sizes were determined. In a third experiment the effects of 1-MCP on ethylene-induced flower abortion in saleable sizes were studied. Saleable sizes of the cultivars Apeldoorn (size 11/12), Christmas Marvel (size 11/12) and Aladdin (size 11/12) were stored in a 2 C room from September 2 till November 18. The bulbs were subjected to the following treatments: - no 1-MCP, no ethylene continuously ( Air control) - exposure to 3 ppm ethylene for 24 h every 4 days in a gas-tight tank - exposure to 3 ppm ethylene for 24 h every 4 days combined with a 1-MCP treatment every 12 days (in gas-tight tanks) The bulbs were cooled, planted on boxes and forced in a greenhouse at 18 C in March the next year. After harvesting, flower length, weight, the number of additional shoots and the percentage of flower abortion were determined. RESULTS Duration of 1-MCP Effect Exposing non-mcp-treated Apeldoorn bulbs to 6 ppm ethylene for 24 h induced 8 to 9% gummosis in these bulbs (results not shown). Ethylene was unable to induce gummosis in 1-MCP treated bulbs until 12 days after the end of the 1-MCP treatment (Fig. 1). After this 12-day period the ethylene sensitivity gradually returned to its original level, causing a gummosis percentage of approximately 2%, 4% and 7% on day 15, 2 and 25 after 1-MCP treatment, respectively. Effects of 1-MCP on Ethylene-induced Splitting Treating planting stock of the cultivars Christmas Marvel and Monte Carlo with ethylene every week during the storage season strongly diminished the yield of saleable sizes in the next growing season compared with the yield of saleable sizes from bulbs that were not treated with ethylene or 1-MCP (the air column, Fig. 2). Treating the bulbs with 1-MCP every 12 days and with ethylene every 7 days resulted in a yield that was not significantly different from the air control, indicating that 1-MCP completely prevented ethylene induced splitting. The cultivars Apeldoorn and Kees Nelis responded in a similar way (results not shown). Effects of 1-MCP on Ethylene-induced Flower Abortion When saleable size bulbs were exposed to ethylene during storage, a high percentage of flower abortion was observed during forcing the following spring (Table 1). In the cultivars Apeldoorn, Aladdin and Christmas Marvel respectively, 19, 49 and 39% flower abortion was induced by exposure to ethylene, compared with 1% for all 3 cultivars in the Air control. In all cultivars ethylene-induced flower abortion was completely prevented by treating the bulbs with 1-MCP every 12 days. Also the negative effects of ethylene on stem length and weight were prevented by 1-MCP. Ethylene caused an increase in the number of additional shoots per plant. The 1-MCP treatment significantly reduced the number of additional shoots to an even lower level than in the Air control (Table 1). The effects on length, weight and additional shoots are only shown for the cultivar Christmas Marvel in Table 1. The cultivars Apeldoorn and Aladdin responded in an identical manner (results not shown). DISCUSSION This study shows that tulip bulbs can be made completely insensitive to ethylene for 12 days by a treatment with 1-MCP and that a prolonged protection from ethylene damage can be achieved by a repeated 1-MCP treatment every 12 days. In previous experiments the optimal 1-MCP concentration was determined. Concentrations of.5 to 244

3 1 ppm 1-MCP and different ethylene concentrations were tested. From these experiments it could be concluded that.2 ppm 1-MCP is the optimal concentration for protecting the bulbs from ethylene concentrations as high as 2 ppm. These results are not shown in this article. The first experiment described in this article shows that a 1-MCP treatment of tulip bulbs offers the bulbs complete protection from ethylene for 12 days. The duration of the 1-MCP effect is shorter than in apples (several months when stored at low temperatures; Fan et al., 1999) and longer than in some plants or fruits. It is assumed that de novo synthesis of ethylene receptors is the cause of the gradual recovery of ethylene sensitivity (Sisler and Serek, 1997). Currently, for bulb transport in sea containers, the bulbs can only be treated before shipping. For shipping periods shorter than 12 days the bulbs will be fully protected from ethylene during transport. When the shipping takes longer than 12 days the ethylene damage during transport will be relatively small compared with the transport of untreated bulbs because the ethylene sensitivity returns to its original level only slowly. After 21 days the ethylene sensitivity is still only 4% of the control situation (Fig. 1). In the other experiments described in this paper it was demonstrated that tulip bulbs can be protected from longer exposure times to ethylene (2 to 3 months) by repeated 1-MCP treatments every 12 days (Fig. 2, Table 1). This offers bulb growers and forcers a solution for the ethylene problem which causes huge financial losses for the bulb industry every year. The commonly used storage rooms on bulb farms are far from gas-tight. Due to leakage of gasses from these rooms the required exposure time and concentration of the 1-MCP treatment might not be met under practical conditions. To test the efficacy of 1-MCP in this type of storage room an experiment was carried out at the experimental bulb farm of Applied Plant Research at St. Maartensvlotbrug in a common type of storage room with planting stock in pallet boxes. A leakage of CO 2 from this room of 5% in 6 h was measured. During the storage period a continuous flow of ethylene from a gas cylinder was applied creating a continuous concentration of 5-1 ppm ethylene. Control samples were removed from the storage room during the 1-MCP treatment. Also in this experiment ethylene-induced splitting was prevented by 1-MCP indicating that the first hours of exposure to the gas are the most important for binding to the ethylene receptors inside the bulbs and that 1-MCP is also effective under practical conditions (results not shown). Early in 24 1-MCP was registered for the use in tulip bulbs under the name FreshStart. ACKNOWLEDGEMENTS This project was financed by the Dutch Ministry of Agriculture, Nature and Food Quality, the Product Board for Horticulture and The Netherlands Agency for Energy and Environment. Literature Cited De Wild, H.P.J., Gude, H. and Peppelenbos, H.W. 22. Carbon dioxide and ethylene interactions in tulip bulbs. Physiol. Plant. 114: Fan, X., Blankenship, S.M. and Mattheis, J.P Methylcyclopropene inhibits apple ripening. J. Amer. Soc. Hort. Sci. 124(6): Kamerbeek, G.A. and de Munk, W.J A review of ethylene effects in bulbous plants. Scientia Hort. 4: Sisler, E.C., Dupille, E. and Serek, M Effect of 1-methylcyclopropene and methylenecy-clopropane on ethylene action on cut carnations. Plant Growth Regul. 18: Sisler, E.C. and Serek, M Inhibitors of ethylene responses in plants at the receptor level: Recent developments. Physiol. Plant. 1:

4 Tables Table 1. Characteristics of Christmas Marvel flowers produced from bulbs stored in an atmosphere without ethylene or 1-MCP (Air), bulbs exposed to 3 ppm ethylene for 24 h every 4 days (Ethylene) or bulbs exposed to 3 ppm ethylene for 24 h every 4 days and treated (24 h) with.2 ppm 1-MCP every 12 days (Ethylene + 1-MCP). Mean values with standard deviation of 4 replicates of 5 bulbs. Figures with a letter in common are not significantly different at p =.5. Weight per flower (g) Length per flower (cm) Number of additional shoots % flower abortion Air 21 a 24 a 4.9 a 1 a Ethylene 15 b 17 b 5.3 a 39 b Ethylene + 1-MCP 21 a 25 a 3.6 b 1 a Figures 8 Duration of 1-MCP effect % Gummosis Days after 1-MCP treatment Fig. 1. Time course of the percentage of bulbs (cv. Apeldoorn; n = 3) showing gummosis after a 24 h exposure to 6 ppm ethylene. The bulbs were treated (24 h) with.2 ppm 1-MCP on day. Percentage of gummosis induced by ethylene in bulbs not treated with 1-MCP:

5 Yield cv. Christmas Marvel Yield cv. Monte Carlo number of saleable sizes a Air Ethylene Ethylene + 1-MCP b 1.2 a a number of saleable sizes Air Ethylene Ethylene + 1-MCP b a Fig. 2. Yield of saleable sizes (expressed as fraction of the number of bulbs planted) from bulbs stored in an atmosphere without ethylene or 1-MCP (Air), bulbs exposed to 15 ppm ethylene for 24 h every 7 days (Ethylene) or bulbs exposed to 15 ppm ethylene for 24 h every 7 days and treated (24 h) with.2 ppm 1-MCP every 12 days (Ethylene + 1-MCP). Mean values with standard deviation of 4 replicates of 3 bulbs. Columns with a letter in common are not significantly different at p =