Genetic Parameters and Genotype–Environment Interactions in Paulownia Clonal Tests in Temperate and Subtropical Regions of China

Clonal forestry has developed rapidly in recent years and already plays a significant role in commercial tree plantations worldwide. Clonal breeding requires accurate assessments of genetic parameters, together with measurements of clonal productivity, stability, and adaptably. However, relevant studies for clones of Paulownia spp. genotypes are rare. We therefore conducted clonal tests on twenty Paulownia clones established at three sites in the temperate and subtropical regions of China. Trees were planted in a randomized block design, with four replications in each site, twenty plots in each block, and six to eight individuals of the same clone in each plot. We measured the trunk diameter at breast height (DBH), total trunk height (Ht), and individual stand volume of 7-year-old trees to estimate genetic parameters and analyze genotype–environment interactions. A combined analysis of variance indicated that clonal, site, and clone–site interactions significantly affected the three growth traits. Clonal heritability and individual heritability were 0.35–0.84 and 0.07–0.30, respectively. The phenotypic and genetic correlation coefficients among the growth traits were 0.46–0.93 and 0.85–0.99, respectively. There were extremely significant positive linear relationships between the best linear unbiased predictors for DBH and the original DBH values (R2 > 0.98). Clones 10, 2, 18, and 13 were selected for deployment based on a selection intensity of 1.4, GGE biplots, and the relative performance of harmonic means on genotypic values analysis. For these clones, the genetic gains in DBH, Ht, and volume were 18.05%, 21.46%, and 46.03%, respectively. These results provide useful information for the selection of Paulownia clones at the target sites and will provide a sound basis for improving Paulownia clonal breeding programs in the future.