43 Inbreeding Depression in Seed-Propagated Lilium x-formolongi Inbreds Neil O. Anderson Bruce Dunn Department of Horticultural Science Dept. of Horticultural Science & University of Minnesota Landscape Architecture 1970 Folwell Avenue Oklahoma State University St. Paul, MN 55108, USA Stillwater, OK 74078, USA Keywords: germination, flowering, leaf number, male sterility, shoot number, pollen stainability, height Abstract Lilium longiflorum, Easter lily, remains among the top ten potted flowering plants in the United States. L. formosanum is a closely related white trumpet lily. Currently one Easter lily cultivar predominates in the U.S. market, ‘Nellie White’. In an effort to increase the crop germplasm base, interspecific hybrids were generated. Commercial, interspecific seed-propagated hybrids, from crossing L. formosanum (female) x L. longiflorum (male), were used in this study. Hybrids segregated for self incompatibility (SI) and self compatibility (SC). SC hybrids were self pollinated to generate 11 F 2 inbred populations (N=151). F 2 seedlings were grown to anthesis under glasshouse conditions of 21°C and long day photoperiods. Data were collected on % pollen stainability, no. days to visible bud, no. days to anthesis (flowering date), plant height, inflorescence length, no. of leaves, internode length, flower bud count, no. of shoots/bulb, stem color, and any morphological abnormalities. A single, dominant gene may control SC. Pollen stainability was significantly lower than the parents in two inbred families, but not significantly different in all others. The no. of days to visible bud ranged from 175 to 253 days, while flowering ranged from 196 to 283 days. All other traits showed significant inbreeding depression and varied depending on the inbred population. Additional abnormal symptoms indicating inbreeding repression included malformed flowers with petals/tepals becoming leaves, lack of anthers or pollen dehiscence. While inbreeding depression is severe, several early flowering inbreds with reduced depression could be selected to continue inbreeding in future generations. INTRODUCTION Commercial potted and cut lilies are primarily vegetatively propagated, rather than sexually (McRae, 1998). Easter lily (Lilium longiflorum) is the best-known trumpet lily. Potted Easter lilies rank in the top ten flowering potted plants sold in the U.S.A., with a $35.273 million wholesale, farm-gate value (U.S. Dept. Agri., 2001). In the U.S.A., Nellie White is the sole Easter lily cultivar grown, while in Europe, Israel, and Japan other cultivars are produced. A related white trumpet lily, L. formosanum, is easily seed-propagated and flowers in the first year after sowing. This species crosses with Easter lily and the hybrids are known as L. x-formolongi (Okazaki, 1996). L. formosanum, a self-compatible (SC) species, is the female parent due to unilateral incompatibility (Ascher and Peloquin, 1968). L. longiflorum, on the other hand, is self-incompatible (SI). The species differ cytologically with L. longiflorum having three more intercalary C-bands than L. formosanum (Smyth, et al., 1989). L. x-formolongi flower within a year from seed; both parental species and the hybrids have white trumpet flowers. L. x-formolongi are currently grown as cut flowers in Japan (Okazaki, 1996). Since the interspecific L. x-formolongi hybrids flower in less than one year from seed and are often SC, inbred lines can be created. Such inbreds would have commercial value to produce uniform hybrid, seed-propagated potted Easter lilies. The research objective of this study was to determine the level of inbreeding depression for several traits (self seed set, SI:SC frequency, pollen stainability, flowering, height, flower Proc. XXVI IHC  Elegant Science in Floriculture Eds. Th. Blom and R. Criley Acta Hort. 624, ISHS 2003 Publication supported by Can. Int. Dev. Agency (CIDA)