SMALL FRUIT AND ORNAMENTAL GENETIC RESEARCH FOR THE MID-SOUTH
Location: Southern Horticultural Research
Title: Evaluation of genetic diversity and pedigree within crapemyrtle (Lagerstroemia spp.) cultivars using simple sequence repeat (SSR) markers
Submitted to: Journal of the American Society for Horticultural Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 8, 2010
Publication Date: March 1, 2011
Citation: Wang, X., Wadl, P.A., Cabrera, R.I., Pounders Jr, C.T., Scheffler, B.E., Pooler, M.R., Rinehart, T.A., Trigiano, R.N. 2011. Evaluation of genetic diversity and pedigree within crapemyrtle (Lagerstroemia spp.) cultivars using simple sequence repeat (SSR) markers. Journal of the American Society for Horticultural Science. 136(2):116-128.
Interpretive Summary: There are more than 50 species of Lagerstroemia, but L. indica and L. fauriei have been the most extensively used in horticultural breeding programs. These species have desirable ornamental traits such as interesting growth habits and bark colors, a wide range of flower colors including white, pink, purple, and red, and resistance to powdery mildew and insect pests. When crossed, L. indica and L. faurei produce various appealing combinations of ornamental traits. Interspecific hybrids between these species are the most popular cultivars in the industry and are often used as parents in crapemyrtle breeding programs. Over 200 named varieties of crapemyrtles exist, with at least half of these available from wholesale and retail nurseries. There are 32 crapemyrtle cultivars that are protected by patents.Genetic variation for crapemyrtle breeding is limited primarily to L. indica and L. fauriei but this existing genetic variability could be efficiently combined in novel ways. The objectives of this study were to compare pedigree information and parentage of selected cultivars released by the U.S. National Arboretum and other breeders with molecular diversity data; to assess the genetic diversity between L. indica and L. fauriei taxa using SSRs; and to evaluate the possible shared haplotypes using pedigree-based analyses. Alleles associated with important horticultural traits could be used to accelerate future crapemyrtle breeding.
Genetic diversity was estimated for 93 crapemyrtle (Lagerstroemia spp.) cultivars (51 L. indica cultivars, 5 L. fauriei cultivars, and 37 interspecific hybrids) using 78 simple sequence repeat (SSR) markers. SSR loci were highly variable among the cultivars, detecting an average of 6.6 alleles per locus. Each locus detected 13.6 genotypes on average. Overall allelic richness was moderately high at 6.4 alleles per locus. Cluster analysis identified three main groups that consisted of individual cultivars from L. indica, L. fauriei and their interspecific hybrids. However, only 18.1% of the overall variation was due to differences between these groups, which may be due to pedigree-based breeding strategies that use current cultivars as parents for future selections. Clustering within each group generally reflected breeding pedigrees but was not supported by bootstrap replicates. Low statistic support was likely due to low genetic diversity estimates, which indicated that only 25.5% of the total allele size variation was due to differences between the species L. indica and L. fauriei. Most allele size variation, or 74.5%, was common to L. indica and L. fauriei. Thus, introgression of other Lagestroemia species, such as L. limii, L. speciosa and L. subcostata may significantly expand crapemyrtle breeding programs. This study verified relationships between existing cultivars and identified potentially untapped sources of germplasm.