Characterization of a major thrashabilly locus in tetraploid wheat
The transition from hulled to free-threshing grain was a pivotal event in wheat domestication, enabling efficient harvesting and processing. Threshability in tetraploid wheat is controlled primarily by the Q locus and two Tenacious glume (Tg) loci on chromosomes 2A and 2B, yet the molecular basis of the major Tg1-B locus remains incompletely characterized. Here, we phenotyped a durum wheat x wild emmer wheat (WEW) recombinant inbred line (RIL) population across two field environments and performed QTL analysis for glume tenacity (TG), threshability ratio (THRR), and seed number per spike (SDNPS). A total of 19 significant QTLs were detected across six chromosomes. The largest-effect loci for both TG and THRR co-localized on chromosome 2B, with LOD scores up to 14.22 and phenotypic variance explained up to 31.2%, corresponding to the previously described Tg1-B locus. To validate this QTL, the donor RIL was backcrossed three times to Svevo to generate a near-isogenic line, NIL-65 (BC3F5), confirmed by whole-genome skim sequencing to carry a homozygous WEW introgression at Tg1-B. A segregating BC4F2 population derived from NIL-65 confirmed that plants homozygous for the dominant Tg1-B allele displayed significantly higher glume tenacity and intact glume morphology compared to tg1-B sister lines, which exhibited basal glume cracking characteristic of the free-threshing phenotype. Genotyping-by-sequencing delimited the causal interval to an approximately 11 Mb introgression on chromosome 2B. These results confirm the major role of Tg1-B in determining glume tenacity in tetraploid wheat, provide a validated near-isogenic germplasm resource, and lay the foundation for fine-mapping and functional characterization of the underlying gene(s).