1 Floral and Nursery Plants Research Unit, U.S. National Arboretum, Agricultural Research Service, U.S. Department of Agriculture, Tennessee State University Nursery Research Center, 472 Cadillac Lane, McMinnville, TN 37110
Japanese snowbell (Styrax japonicus Sieb. & Zucc.) is an outstanding small ornamental tree that is underused in the U.S. One of the reasons this Asian native is not more widely planted is that it is subject to spring freeze damage. The objectives of this study were to determine if there was variability within S. japonicus for time of budbreak and if this variability could be used for selecting plants better adapted to areas of the country that frequently experience late spring freezes. During Spring 1999 and 2000, budbreak was evaluated weekly in 224 open-pollinated seedlings. While weather conditions varied greatly between the 2 years, there was good consistency between 1999 and 2000 data. There was a 4-week difference between the earliest and latest plants to break dormancy. Based on the 1999 and 2000 data, 28 plants were selected and propagated. A replicated trial involving these selections and three cultivars was carried out in 2002, 2003 and 2004. All of the selections broke bud later and suffered less freeze damage than the cultivars `Emerald Pagoda' and `Carillon', but many performed similarly to `Pink Chimes'. Variation in height, width, caliper and canopy shape was observed among the selections. There is an opportunity to utilize the genetic variability in S. japonicus for developing cultivars with reduced susceptibility to spring freeze damage.
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