Genetic characterization of Liriodendron seed orchards with EST-SSR markers

Liriodendron tulipifera L., is a wide-spread, fast-growing pioneering tree species native to eastern North America. Commonly known as yellow-poplar, tulip tree, or tulip-poplar, the species is valued, both ecologically and economically. It is perhaps the most commonly used utility hardwood in the USA, and is planted widely for reforestation and, in varietal forms, as an ornamental. Although most seedlings used for reforestation today derive from collections in natural populations, two known seed orchards, established from plus-tree selections, i.e. superior phenotypes, in the 1960’s and 1970’s have been used for local and regional planting needs in Tennessee and South Carolina. However, very little is known about the population genetics of yellow-poplar nor the genetic composition of the existing seed orchards. In this study, 194 grafted yellow-poplar trees from a Clemson, SC orchard and a Knoxville, TN orchard were genetically characterized with 15 simple sequence repeat (SSR) markers developed from expressed sequence tags (ESTs). Of the 15 EST-SSR markers, 14 had a polymorphic information content (PIC) of at least 0.5. There was no significant difference between the Clemson and Knoxville orchards in average effective number of alleles (5.93 vs 3.95), observed and expected heterozygosity (Ho: 0.64 vs 0.58; He: 0.74 vs 0.70), Nei’s expected heterozygosity (0.74 vs 0.58), or Shannon’s Information index (1.84 vs 1.51). The larger Clemson orchard exhibited a significantly greater number of observed alleles than the Knoxville orchard (15.3 vs7.4). Overall, substantial genetic diversity is captured in the Clemson and Knoxville orchards.