Population and Phenotypic Data

Correlative association population used in this study was composed of 435 unrelated Populus tomentosa individuals from a collection in Guan Xian town, Shandong province (China, 36°23′N, 115°47′E), covering nearly all the natural distribution individuals of Populus tomentosa species, including the northwestern, southern, and northeastern regions of China (30–40°N, 10–125°E) (Du et al., 2012). These 435 individuals were used to discover single nucleotide polymorphism (SNP)s within candidate FRK genes.

We used three growth traits and seven wood property traits for the association analysis. The seven wood properties were as follow: holocellulose content (HC, %), lignin content (LC, %), α-cellulose content (CC, %), hemicellulose content (HEC, %), fiber length (FL, mm), fiber width (FW, μm), and microfibril angle (MFA, °). The three growth traits were as follow: diameter at breast height (DBH, cm), tree height (H, m), and stem volume (V, m³). Relevant measurement methods of the phenotypic data for the 435 genotypes were described in previous study (Du et al., 2014).