1 Floral and Nursery Plants Research Unit, U.S. National Arboretum, Agricultural Research Service, U.S. Department of Agriculture, Tennessee State University Nursery Crop Research Station, 472 Cadillac Lane, McMinnville, TN 37110
2 Floral and Nursery Plants Research Unit, U.S. National Arboretum, Agricultural Research Service, U.S. Department of Agriculture, 10300 Baltimore Avenue, Beltsville, MD 20705
The genus Clethra contains many ornamental species, of which the most adaptable and cold hardy is C. alnifolia L. The objective of this study was to obtain hybrids between C. alnifolia and three other ornamental Clethra species, C. acuminata Michx., C. fargesii Franch., and C. pringlei S. Wats. Viable plants were obtained from reciprocal crosses between C. alnifolia and C. fargesii, and from crosses between C. alnifolia and the other two species when C. alnifolia was used as the maternal parent. Randomly amplified polymorphic DNA (RAPD) markers were used to verify hybridity and to compare hybrids to their parents. In all cases, the hybrids had more RAPD markers in common with C. alnifolia than with their other parent. Close clustering by neighbor-joining analysis of RAPD markers and the morphological resemblance of C. alnifolia × C. acuminata and C. fargesii × C. alnifolia plants to their paternal parent indicated that these plants were of hybrid origin. The C. alnifolia × C. pringlei plants resembled C. alnifolia in many respects, but they stayed green much later in the year than did C. alnifolia with leaves remaining on the plants throughout the winter. These foliage characteristics were presumed to reflect the contribution of the evergreen C. pringlei, and thus were regarded as evidence of hybridity.
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