Selective sweep and GWAS provide insights into adaptive variation of <i>Populus cathayana</i> leaves

Leaf morphology plays a crucial role in predicting the productivity and environmental adaptability of forest trees, making it essential to understand the genetic mechanisms behind leaf variation. In natural populations of Populus cathayana, leaf morphology exhibits rich intraspecific variation due to long-term selection. However, there have been no studies that systematically reveal the genetic mechanisms of leaf variation in P. cathayana. To fill this gap and enhance our understanding of leaf variation in P. cathayana, we collected nine leaf traits from the P. cathayana natural population, consisting of 416 accessions, and conducted the preliminary classification of leaf types with four categories. Subsequently, we conducted an analysis of selective sweep and genome-wide association studies (GWAS) to uncover the genetic basis of leaf traits variation. Most of the leaf traits displayed significant correlations, with broad-sense trait heritability ranging from 0.38 to 0.74. In total, three selective sweep methods ultimately identified 278 positively selected candidate regions and 493 genes associated with leaf size. Single-trait and multi-trait GWAS methods detected 13 and 59 genes, respectively. By integrating the results of selective sweep and GWAS, we further identified a total of nine overlapping genes. These genes may play a role in the leaf development process and are closely associated with leaf size. In particular, the gene CBSCBSPB3 (Pca07G009100) located on chromosome 7, was associated with the response to light stimulation. This study will deepen our understanding of the genetic mechanism of leaf adaptive variation in P. cathayana and provide valuable gene resources.