Liriodendron is a genus of the magnolia family (Magnoliaceae) in the order Magnoliales. The genus consists of two species, with one native to eastern North America (Liriodendron tulipifera) and another to China and Vietnam (Liriodendron chinense). Commonly known as yellow-poplar, tulip tree, or tulip-poplar, L. tulipifera is a wide-spread, fast-growing pioneering hardwood species with considerable economic and ecological values. 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, TN orchard were genetically characterized with 15 simple sequence repeat (SSR) markers developed from expressed sequence tags (ESTs). The Tennessee Knoxville was established in 1966 and contains 100 grafted ramets, representing 31 genotypes or clones. The Clemson orchard was established in 1976 by grafting multiple ramets of 150 plus trees selected from throughout the 17,500-acre Clemson Experimental Forest. Currently there are 165 surviving trees in the Clemson orchard. Seeds from the orchards have been used for reforestation efforts for a number of years. Of the 15 EST-SSR markers, we found that 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 vs 7.4). Overall, substantial genetic diversity is captured in the Clemson and Knoxville orchards.
With a widespread range of distribution, L. tulipifera has adapted to many different ecological conditions and is one of the species becoming increasingly dominant in forests due to its quick respond to increases in light to the forest floor and rapid initial growth rate. Its increasingly important roles in forestry and wood products is making studying Liriodendron of great interest. Our study provides a first look at the genetic diversity and allele richness among selections of this species, and provides a foundation for further genetic and breeding exploration.