Independent genome-wide association mapping confirms a major genomic region associated with curly wood formation in Betula pendula var. carelica

Curly birch ( Betula pendula Roth var. carelica (Mercklin) Hämet-Ahti) is a rare and highly valued tree characterized by a distinctive figured wood phenotype, but the genetic basis of this trait remains unresolved. Here, we independently tested and refined a chromosome 10 region previously associated with curly wood formation. A ddRADseq-based GWAS in 96 unrelated birches confirmed the major association previously detected in full-sib families. Whole-genome resequencing of four curly and two non-curly trees identified 1,872 SNVs within the previously defined ~ 1.2 Mb interval, which were subsequently subjected to annotation-guided prioritization and KASP/STS marker testing. Local linkage disequilibrium analysis further defined an ~ 275 kb LD-enriched interval (3,249,985–3,524,841 bp) containing 22 annotated protein-coding loci. Several annotation-prioritized variants within this interval showed strong and reproducible marker-phenotype associations in both unrelated and full-sib populations, although none have yet been established as causal. The reproducibility of the chromosome 10 association across independent sample designs supports a major-locus architecture of curly wood formation. The refined interval provides a focused target for identifying the causal variation and for further validation of molecular markers for early selection.