The Effects of Precooling Temperatures and Durations on Forcing of Lilium longiflorum, Nellie White Frankie L. Fanelli 1 Department of Horticultural Science North Carolina State University Raleigh, NC 27695-7609. Raleigh, NC 27695-7609 Tel: 1-919-515-1184 Tel: 1-919-515-1184 A.A. De Hertogh Department of Horticultural Science North Carolina State University Fax: 1-919-515-7744. Fax: 1-919-515-7744 E-mail: flfanell@mindspring.com E-mail: gus_dehertogh@ncsu.edu Keywords: Bulb maturity, cold-weeks, Easter lily, flower bulbs, forcing Abstract California-grown bulbs of Lilium longiflorum Nellie White (23/25 cm, in circumference) were precooled (PC) for 5, 6, or 7 weeks at 2, 5, or 7C. Prior to PC, the percent of bulbs with the meristem off the basal plate was 10, 10, and 0 percent for 2, 5, and 7C, respectively. After PC, the peat moisture content was 55, 43, and 55 percent for 2, 5, and 7C, respectively. Standard greenhouse forcing procedures were used. The fewest greenhouse days to flowering occurred with 6 weeks at 5 and 7C, and 7 weeks at 2, 5, and 7C. The earliest flowering dates were obtained with 5 and 7C with 5 or 6 weeks of PC. The latest dates of flowering were obtained with 2C at 5, 6, or 7 weeks and 5 and 7C for 7 weeks. The highest flower numbers were obtained with 2C with 5 weeks of PC and 7C with 5 and 6 weeks PC. The lowest flower numbers were obtained with 7 weeks of PC at 5 or 7C. The treatment that reduced total plant height was 7C for 7 weeks of PC, but it was not significantly different from six other treatments. The highest leaf numbers were obtained with 5C for 5, 6, or 7 weeks of PC. There was no difference in plant quality among the nine treatments. Thus, early flowering bulbs should be PC at 5C for 5 or 6 weeks; while for late flowering 2C for 5 or 6 weeks should be used. INTRODUCTION In North America, Lilium longiflorum Thunb. is primarily used as a forced flowering potted plant for Easter and there are three forcing goals (De Hertogh 1996). They are: (1) precise timing for Easter (Table 1), (2) maximizing the number of flowers produced, and (3) optimum height control of marketable plants. In the U.S., it has been reported that this crop represents five percent of the pot plant market (Miller 1999) and the annual value is about $45 million (USDA-NASS 1999). Currently, Nellie White is the only cultivar produced in California and Oregon for this market (R.O. Miller, Personal Communications). Since Easter varies annually (Table 1), it is essential that bulb forcers know precisely how to program this cultivar in order to have high quality plants available for Easter regardless of the date. Miller and Kiplinger (1966) have shown that temperature and duration significantly affect the flowering of Ace. No similar study has been conducted on Nellie White. In general, this cultivar has been programmed using 4 to 5 C. However, because of the commercial importance of Nellie White, this study was carried out to determine the effects of various PC temperatures and duration on its flowering and other horticultural characteristics. MATERIALS AND METHODS Nellie White bulbs (23/25 cm in circumference) were harvested in Northwest California in September, 1998. They were packed in moist peat in wooden boxes, stored under prevailing temperatures, and shipped to the United Bulb Company in Mt. Clemens, Michigan by refrigerated (2C) transport. The bulbs were stored for 3 days at 6-7C before being shipped to Raleigh, North Carolina on October 21, 1998 via United Parcel Service. Upon arrival on October 26, 1998, 300 bulbs were divided into three equal temperature Proc. 8th Int. Symp. on Flowerbulbs Eds. G. Littlejohn et al. Acta Hort. 570, ISHS 2002 147
groups. Subsequently, 10 bulbs of each temperature group were examined to determine the internal condition of the bulbs. The results were: (1) the 2C bulbs were 10 percent off the basal plate (approximately 2 mm) with some interior scale rot, (2) the 5C bulbs were 10 percent off the basal plate (3 mm) with some interior scale rot, and (3) the 7C bulbs were 0 percent off the basal plate and no interior scale rot. The wooden boxes with 90 bulbs in moist peat were stored at 17C until October 29, 1998, when the treatments were placed at 2, 5, or 7C. The percent moisture of the peat (after 7 weeks of PC) was 55, 43, and 55 percent for 2, 5, and 7C, respectively. A preplant fungicidal bulb dip of Etridiazole plus Thiophanate-methyl (Banrot ; The Scotts Company, Marysville, Ohio) was used at a rate of 19 grams per 11.4 liters of water for 5 minutes prior to planting. One bulb was planted per 15-cm diameter, standard depth plastic pot utilizing a peat and perlite planting media (Sunshine Mix No. 4; Fisons Horticulture, Vancouver, B.C.). The planting dates were December 3, 1998 (5 weeks PC), December 10, 1998 (6 weeks PC), and December 17, 1998 (7 weeks PC). At each planting the internal condition of 10 bulbs was determined (Table 2). Twenty pots (4 replications with 5 observations each) were used per temperature and duration treatment (Table 3). The pots were placed in the greenhouse (Latitude 35 46 N, Longitude 78 40 W) in a randomized complete block design. The plants were grown with night/day temperatures of 16-17/20-23C and prevailing light conditions (8.1 to 20.9 MJ d -1 from January through May). Six grams of 14-14-14 (14-6.2-11.6) Osmocote TM (The Scotts Company, Marysville, Ohio) were applied per pot at shoot emergence. Subsequently, a supplemental liquid fertilizer of Ca (NO 3 ) 2 at a rate of 27.3 grams per 11.4 liters and KNO 3 at a rate of 14.5 grams per 11.4 liters of water was applied twice weekly. A fungicidal drench of Etridiazole plus Thiophanate-methyl was applied at a rate of 19 grams per 11.4 liters of water every 4 weeks. The following data was collected and recorded for each plant. The number of greenhouse days to flowering was calculated based on the date the plant was placed in the greenhouse until the first flower opened. The days from buds visible to flowering followed the procedures of Roh and Wilkins (1973). All other data was collected on the date of flowering. They were: (1) total plant and pedicel height measured (cm) from the pot rim to the upper most part of the inflorescence and pedicel, respectively; (2) the length and width of the leaves measured (cm) at pot and half plant level; (3) the number of green, brown, and total leaves; (4) presence of leaf scorch; (5) the number of initial and raised primary, secondary, and total flowers; (6) presence of stem strength; and (7) overall plant quality. All data was analyzed as a randomized complete block using Macintosh SAS version 6.12. RESULTS AND DISCUSSION There were no significant differences in overall plant market quality among the nine PC treatments. The range was 3.7 to 3.9 out of 4.0. Thus, all plants were excellent quality. The lengths and widths of the leaves at pot and half plant level, the number of green leaves, the presence of leaf scorch, and stem strength were not significantly different among the treatments. Thus, we only discuss the three primary forcing goals for potted Easter lilies in North America. They are: (1) timing, (2) flower number, and (3) plant height (De Hertogh 1996). De Hertogh and Wilkins (1971) indicated that at least 11 factors can affect the timing of Easter lilies. Three major factors are: (1) bulb maturity (meristem movement off the basal plate), (2) the moisture content of the peat, and (3) temperature and duration of the programming treatment. In this experiment, the moisture of the peat after seven weeks of PC was 43 to 55 percent. They were in the acceptable moisture range for programming (Prince and Cunningham 1990). Also, bulb maturity at the start of all the PC treatments was low (immature) since fewer than 10 percent had elongated were not off the basal plate. Thus, this programming parameter was optimal to determine the effects of the PC 148
treatments. Precise timing for Easter (Table 1) must consider not only the number of greenhouse days to flowering but also the actual date of flowering (Table 3). With the exception of the two weeks difference in PC and planting, all plants in this experiment were subjected to the same greenhouse environment. No treatments were used to accelerate or delay flowering. These procedures were utilized in order to determine natural earliness and/or lateness of the programming treatments. The fewest greenhouse days to flowering were 119 to 121 days and they were obtained with 2, 5, and 7C for 7 weeks and 5 and 7C for 6 weeks. The greatest number of greenhouse days to flowering was 133 days and these bulbs received 2C for 5 PC weeks. The earliest dates of flowering were obtained with 5 and 7C with 5 or 6 PC weeks. The latest dates of flowering resulted from 2C for 5, 6, or 7 weeks. These data results are consistent with those of Miller and Kiplinger (1966) who PC Ace lilies for 0 to 7 weeks at 4-6C. Although there were significant differences in greenhouse days to flowering (Table 3), from visible bud, the range was extremely small (1.3 days). To significantly change the number of days for this stage of floral development, greenhouse temperatures have to be adjusted (Erwin and Heins 1990, Roh and Wilkins 1973). The highest flower number was obtained with seven treatments (Table 4). Only 7 weeks of PC at 5 or 7C reduced the number of flowers. These results are in agreement with those of Miller and Kiplinger (1966) who used Ace bulbs. They showed a decline in the number of flowers with increasing numbers of cold weeks. There was however, a marked change in the type of flowers (De Hertogh et al. 1976) produced (Table 4). Compared to other PC treatments, 7 weeks of PC at 2, 5,or 7C and 2C for 6 weeks produced significantly less initial primary flowers. However, the total number of flowers was not significantly different except for 5 and 7C for 7 weeks. In addition, 7C for 6 weeks and 5C for 7 weeks produced a few secondary flowers. These modifications of flower types have been reported by applying changes in greenhouse forcing temperatures by De Hertogh et al. (1976) and Kohl (1958) for Ace. All treatments produced plants with acceptable marketable heights. Although there were significant statistical differences in the plant heights to the pedicel and lengths of the leaves at the half plant level, the differences were extremely small. The shortest plants were obtained with 7 PC weeks and 7C. Easter lily height is affected by at least 12 factors (De Hertogh and Wilkins 1971). Therefore, the growth rate in the greenhouse must be carefully monitored and managed by calculating the leaf unfolding rate and using low day/high night temperatures (Hammer and Hopper 1989, Karlsson et al. 1988, Lieth and Carpenter 1990). The highest number of leaves was produced with 5C at 5, 6, and 7 weeks of PC. The fewest number of leaves was produced with 2 C for 6 or 7 weeks of PC and 7 C for 7 weeks. In some instances, these treatments were not significantly different from other treatments. Thus, this may be a trend and needs to be verified. The fewest number of lower brown leaves were obtained with 2 and 7C for 7 weeks. This could be a reflection of differences in senescence, root rot, and/or the total number of leaves produced by the treatment. CONCLUSIONS In Table 6, we summarized the essential characteristics of the programming treatments. For early forcing, it appears that 5 C for 5 or 6 weeks is the best programming treatment; while 2C for 5 or 6 weeks is optimum for late flowering. In addition to the programming treatments used, continued monitoring of the crop must be conducted utilizing the techniques and practices summarized in the Holland Bulb Forcer s Guide (De Hertogh 1996). These include: (1) the use of long days at emergence for programming for early Easters and/or very immature bulbs (Dole 1993; Dole and Wilkins 1994), (2) adjusting the greenhouse temperatures based on the rate of leaf unfolding (Karlsson et al. 1988), and (3) the use of exogenous plant growth regulators for marketable plant height control (Jiao et al. 1990). 149
Additional research is needed to confirm the results of this study using not only PC bulbs but also the programming for controlled-temperature forcing. In addition, the possibility of using temperature combinations with proper moisture levels for programming should be examined. For example, it may be possible to use 5 or 7 C for 3 weeks followed by 3 or 4 weeks at 2 C. These studies must include periodic examinations of the bulbs for: (1) stage of maturity, (2) meristem size, and (3) floral development. ACKNOWLEDGEMENTS The authors thank the United Bulb Company, Mt. Clemens, Michigan for supplying the bulbs. Literature Cited De Hertogh, A. 1996. Holland bulb forcer s guide. 5 th ed. International Flower Bulb Centre, Hillegom, The Netherlands. De Hertogh, A., Rasmussen, H.P. and Blakely, N. 1976. Morphological changes and factors influencing shoot apex development of Lilium longiflorum Thunb. during forcing. J. Amer. Soc. Hort. Sci. 101(4):463-471. De Hertogh, A. and Wilkins, H.F. 1971. The forcing of northwest-grown Ace and Nellie White Easter lilies. Florists Review. 149 (3858):104-111. Dole, J.M. 1993. Interaction of shoot emergence date and long days after controlledtemperature forcing of Nellie White Easter lilies. J. Amer. Soc. Hort. Sci. 118 (6):741-746. Dole, J.M. and Wilkins, H.F. 1994. Interaction of bulb vernalization and shoot photoperiod on Nellie White Easter lily. HortScience. 29(3):143-145. Erwin, J.E. and Heins, R.D. 1990. Temperature effects on lily development rate and morphology from the visible bud stage until anthesis. J. Amer. Soc. Hort. Sci. 115 (4):644-646. Hammer, P.A. and Hopper, D.A. 1989. Modeling stem elongation of Easter lilies grown under various production schemes. HortScience. 24(5):785-788. Jiao, J., Wang, X. and Tsujita, M.J. 1990. Comparative effects of uniconazole drench and spray on shoot elongation of hybrid lilies. HortScience. 25 (10):1244-1246. Karlsson, M.G., Heins, R.D. and Erwin, J.E. 1988. Qualifying temperature-controlled leaf unfolding rates in Nellie White Easter lily. J. Amer. Soc. Hort. Sci. 113(1):70-74. Kohl, H.C. Jr. 1958. Effects of temperature variation on forced Lilium longiflorum var. Ace. Proc. Amer. Soc. Hort. Sci. 72:477-480. Lieth, J.H. and Carpenter, P. 1990. Modeling stem elongation and leaf unfolding of Easter lily during greenhouse forcing. Scientia Hortic. 44:149-162. Miller, M.N. 1999. A year of change. GrowerTalks. 63(6):10-12, 14, 16, 19, 20. Miller, R.O. and Kiplinger, D.C. 1996. Interaction of temperature and time of vernalization on northwest Easter lilies. Proc. Amer. Soc. Hort. Sci. 88:635-645. Prince, T.A., and Cunningham, M.S. 1990. Response of Easter lily bulbs to peat moisture content and the use of peat or of polyethylene-lined cases during handling and vernalization. J. Amer. Soc. Hort. Sci. 115(1):68-72. Roh, S.M. and Wilkins, H.F. 1973. Influence of temperature on the development of flower buds from the visible bud stage to anthesis of Lilium longiflorum Thunb. Cv. Ace. HortScience 8(2):129-130. USDA-NASS. 1999. Floricultural crops 1998 summary. U. S. Government Printing Office, Washington DC. 150
Tables Table 1. Easter dates for 2001 to 2012. Year Date Year Date 2001 April 15 2007 April 8 2002 March 31 2008 March 23 2003 April 20 2009 April 12 2004 April 11 2010 April 4 2005 March 27 2011 April 24 2006 April 16 2012 April 8 Table 2. Meristem condition of 10 bulbs per temperature treatment of Lilium longiflorum Nellie White on date of planting. Temperature Planting date (C) December 3 December 10 December 17 2 20% off basal plate (1 to 2 mm with a mean of 1.5 mm) 30% off basal plate (1 to 3 mm with a mean of 2 mm) 60% off basal plate (1 to 4 mm with a mean of 2.2 mm) 5 80% off basal plate (2 to 5 mm with a mean of 3.5 mm) 7 70% off basal plate (2 to 4 mm with a mean of 2.9 mm) 60% off basal plate (1 to 12 mm with a mean of 5 mm) 60% off basal plate (1 to 58 mm with a mean of 12.5 mm) 100% off basal plate (1 to 6 mm with a mean of 3.1 mm) 70% off basal plate (2 to 4 mm with a mean of 2.7 mm) Table 3. Effects of precooling temperature and duration on greenhouse days to flowering, date of flowering, and days from visible bud to flowering of Lilium longiflorum Nellie White. PC Temperature Flowering Days from visible (C/weeks) Days Date bud to flowering 2/5 133 a April 15 40.0 ab 5/5 128 b April 11 41.1 a 7/5 128 b April 11 39.9 ab 2/6 125 bc April 14 40.1 ab 5/6 121 cd April 11 40.5 ab 7/6 121 cd April 11 40.1 ab 2/7 119 d April 16 40.6 ab 5/7 120 d April 15 39.8 b 7/7 119 d April 15 41.1 a 151
Table 4. Effects of precooling temperature and duration on total number of flowers, initial and raised primary flowers, and secondary flowers of Lilium longiflorum Nellie White. PC Treatment Flowers (C/weeks) Total Initial primary Raised primary Secondary 2/5 6.4 a 4.1 ab 2.3 ab 0.0 5/5 6.3 ab 4.3 a 2.1 ab 0.0 7/5 6.4 a 3.9 a-c 2.3 ab 0.2 2/6 5.9 ab 3.5 b-d 2.6 a 0.0 5/6 6.3 ab 4.1 ab 2.3 ab 0.0 7/6 6.6 a 4.3 a 2.3 ab 0.0 2/7 5.9 ab 3.4 dc 2.4 ab 0.0 5/7 5.4 b 3.1 d 1.9 b 0.4 7/7 5.5 b 3.1 d 2.3 ab 0.0 Table 5. Effects of precooling temperature and duration on total plant height, height to pedicel, length of leaves at pot and half plant level, total number of leaves, and number of brown leaves of Lilium longiflorum Nellie White. Plant height (cm) Leaves PC treatment Half plant Total No. (C/weeks) Total To pedicel level (cm) Total of brown 2/5 40.5 ab 16.7 ab 10.5 cd 89 b-d 18 a 5/5 39.7 ab 17.5 ab 10.3 d 97 a 16 ab 7/5 42.6 a 17.9 ab 11.3 ab 88 cd 15 ab 2/6 42.2 a 18.3 a 11.6 a 84 de 16 ab 5/6 39.8 ab 17.9 ab 11.0 bc 96 ad 16 ab 7/6 40.0 ab 17.4 ab 10.7 cd 84 de 15 ab 2/7 40.9 ab 18.2 ab 11.8 a 77 e 11 c 5/7 40.6 ab 17.5 ab 10.8 cd 93 a-c 18 a 7/7 38.5 b 16.3 b 11.0 bc 82 de 14 b Table 6. Summary of essential horticultural characteristics of case precooled and forced Lilium longiflorum Nellie White. PC treatment (C/weeks) Programming habit Total flowers Total plant height (cm) Total leaves 2/5 Late 6.4 a 40.5 ab 89 b-d 5/5 Early 6.3 ab 39.7 ab 97 a 7/5 Early 6.4 a 42.6 a 88 cd 2/6 Late 5.9 ab 42.2 a 84 de 5/6 Early 6.3 ab 39.8 ab 96 ad 7/6 Early 6.6 a 40.0 ab 84 de 2/7 Late 5.9 ab 40.9 ab 77 e 5/7 Late 5.4 b 40.6 ab 93 a-c 7/7 Late 5.5 b 38.5 b 82 de 152