Flowering, potted Easter lilies ranked among the top five potted flowering plants for economic value in the United States in 2004, with more than 9.3 million pots produced and a wholesale value of about $38.5 million (U.S. Department of Agriculture, 2005). Current Easter lily bulb propagation and field production for the North American market relies on one cultivar, Nellie White (>60-year-old clone), produced by less than 10 growers in a small coastal region between Smith River, Calif., and Brookings, Ore. (Dole and Wilkins, 1999; Zlesak and Anderson, 2003). Easter lily bulbs are 2 or 3 years old when field bulb producers ship them to greenhouse finishers. Bulbs are graded and sold according to bulb circumference: 17.8 to 20.3 cm, 20.3 to 22.9 cm, 22.9 to 25.4 cm, and more than 25.4 cm (Dole and Wilkins, 1999).
Although one clone predominates, greenhouse forcers recognize differences in forcing quality across grower bulb lots and years (Zlesak and Anderson, 2003). Forcers react by typically purchasing bulbs from multiple growers annually to ensure a salable crop during the narrow U.S. Easter lily marketing window, which is the 2 weeks before Easter (Zlesak and Anderson, 2003). Variability in forced plants [e.g., days to stem emergence (SEM), leaf number, flower number, internode length] can be attributed to factors such as variable temperatures during shipping and rooting, and variable bulb maturity and dormancy across bulb lots and years (Erwin and Engelen-Eigles, 1998). In addition, production duration and schedules change annually because the date of Easter is variable (22 Mar. to 25 Apr.), whereas greenhouse finishers consistently obtain harvested bulbs at the same time each year (weeks 42–44). To have salable, flowering plants within the 2 weeks before Easter, greenhouse finishers manipulate vernalization treatments, long-day photoperiod treatments after vernalization, and production temperatures. These production factors can alter plant morphology and therefore plant quality (Dole and Wilkins, 1999). Key traits that command a higher market price include high flower bud number, short plant stature (30–46 cm), and developmental milestones occurring in a timely manner to have the first flower opening within 2 weeks before Easter (Dole and Wilkins, 1999; Lange and Heins, 1990; Pi Alpha Xi, 1986; Wilkins and Roh, 1976).
There is the potential for mutation and other genetic changes within and across grower stocks of clonally propagated crops that can lead to variability in morphology (Veilleux and Johnson, 1998). ‘Nellie White’ is more than 60 years old and has emerged as the primary U.S. cultivar, almost to the exclusion of all others (Zlesak and Anderson, 2003). To minimize phenotypic variability during bulb production, Easter lily field growers independently select and propagate their own intraclonal strains (Zlesak and Anderson, 2003). Periodically (≈10 years), growers identify superior-performing lilies within the field with desirable production traits such as late stem emergence from the soil to avoid spring hail storms, quick growth to compensate for late emergence, high flower bud number, compact plants, and lack of premature daughter bulb sprouting (summer sprouting) before harvest (Zlesak and Anderson, 2003). Each grower prioritizes phenotypic characteristics during intraclonal selection according to their production needs and phenotypic preferences. Propagules from each intraclonal selection are kept distinct, and eventually those selections that are uniform and continue to perform well are propagated for commercial production (Zlesak and Anderson, 2003). As variability accumulates among ramets over clonal cycles, intraclonal selection is repeated.
As growers independently perform intraclonal selection and more cycles of intraclonal selection accrue, there is a greater possibility for genetic divergence among grower stocks of ‘Nellie White’. A survey of the relative performance of Easter lily bulb lots across the major growers has not been reported before. The objectives of this research were to determine 1) the extent of morphological variability of L. longiflorum ‘Nellie White’ among bulb lots from different growers across forcing cycles and years, and 2) the sources of the morphological variability.
Allen, T.C., Ballantyne, O., Goodell, J., Anderson, W.C. & Lin, W. 1980 Recent advances in research on lily symptomless virus Acta Hort. 109 479 485
Allen, T.C., Linderman, R.G., McRae, E.A. & Fernald, K. 1974 Performance of virus-free ‘Enchantment’ lilies North Amer. Lily Soc. Yrbk. 27 42 44
De Hertogh, A.A., Carlson, W.H. & Kays, S. 1969 Controlled temperature forcing of planted lily bulbs J. Amer. Soc. Hort. Sci. 94 433 436
De Hertogh, A.A., Rasmussen, H.P. & Blakely, N. 1976 Morphological changes and factors influencing shoot apex development of Lilium longiflorum Thunb. during forcing J. Amer. Soc. Hort. Sci. 101 463 471
Erwin, J.E. & Engelen-Eigles, G. 1998 Influence of simulated shipping and rooting temperature and production year on Easter lily (Lilium longiflorum Thunb.) development J. Amer. Soc. Hort. Sci. 123 230 233
Fay, M.F., Cowan, R.S. & Leitch, I.J. 2005 The effects of nuclear DNA content (C-value) on the quality and utility of AFLP fingerprints Ann. Bot. (Lond.) 95 237 246
Hale, A.L., Miller, J.C., Renganayaki, K., Fritz, A.K., Coombs, J.J., Frank, L.M. & Douches, D.S. 2005 Suitability of AFLP and microsatellite marker analysis for discriminating intraclonal variants of the potato cultivar Russet Norkotah J. Amer. Soc. Hort. Sci. 130 624 630
Larkin, P.J. & Scowcroft, W.R. 1981 Somaclonal variation: A novel source of variability from cell culture for plant improvement Theor. Appl. Genet. 60 197 214
Lim, K.B., Wennekes, J., de Jong, J.H., Jacobsen, E. & van Tuyl, J.M. 2001 Karyotype analysis of Lilium longiflorum and L. rubellum by chromosome banding and fluorescence in situ hybridization Genome 44 911 918
Lin, W.C. & Wilkins, H.F. 1973 The interaction of temperature on photoperiodic responses of Lilium longiflorum Thunb. Cv. ‘Nellie White.’ Florists Rev. 153 24 26
Linderman, R.G., Ames, R.N., Allen, T.C. & Ballentyne, O. 1976 Current efforts to eliminate viruses from Easter lilies in tissue culture North Amer. Lily. Soc. Yrbk. 29 106 108
Miller J.C. Jr, Tai, G.C.C., Ouellette, B. & Miller, J.P. 2004 Discriminating Russet Norkotah intraclonal selections using canonical and cluster analysis Amer. J. Pot. Res. 81 203 207
U.S. Department of Agriculture 2005 Floriculture crops 2004 summary. Sp Cr 6-1 (05) 1 Nov. 2005<http://usda.mannlib.cornell.edu/reports/nassr/other/zfc-bb/floran05.pdf>
U.S. Naval Observatory 2000 Rise and set for the sun for 2000. Astronomical Applications Department 30 June 2006<http://aa.usno.navy.mil/cgi-bin/aa_rstablew.pl>
Van Schadewijk, A.R. 1986 Detection of tulip breaking virus and lily symptomless virus in lily by means of ELISA Acta Hort. 177 121 128
Veilleux, R.E. & Johnson, A.A.T. 1998 Somaclonal variation: Molecular analysis, transformation interaction, and utilization Plant Breed. Rev. 16 229 268
Villordon, A.Q. & LaBonte, D.R. 1996 Genetic variation among sweet potatoes propagated through nodal and adventitious sprouts J. Amer. Soc. Hort. Sci. 121 170 174
Weiler, T.C. & Langhans, R.W. 1968 Determination of vernalizing temperatures in the vernalization requirement of Lilium longiflorum (Thunb.) cv “Ace.” Proc. Amer. Soc. Hort. Sci. 93 623 629
Weising, K., Nybom, H., Wolff, K. & Kahl, G. 2005 DNA fingerprinting in plants: Principles, methods, and applications 2nd ed. CRC Press Boca Raton, Fla
Wilkins, H.F. 2005 Lilium longiflorum Thunb.: A classic model to study temperature and photoperiod interactions on dormancy, flower induction, leaf unfolding, and flower development Acta Hort. 673 293 296
Wilkins, H.F. & Roh, S.M. 1976 Even higher flower bud numbers are now possible in Easter lilies by dipping your greenhouse temperature Minnesota State Florist Bul. Dec 8 12