Genetic diversity of Xizang Brassica rapa and its application in rapeseed breeding via hexaploid bridge lines

Rapeseed ( Brassica napus , AACC), a globally important oilseed crop, suffers from a narrow genetic base that constrains the improvement of yield and stress tolerance. Its progenitor species, B. rapa (AA), possesses extensive genetic diversity that could potentially broaden the genetic base of B. napus . Previous studies indicate that Xizang B. rapa constitutes a unique genetic pool. This study aimed to assess the genetic diversity of Xizang B. rapa and its potential to expand the genetic base of B. napus . A collection of 95 Xizang B. rapa and 44 other B. rapa accessions from various regions in the world were analyzed using SSR markers. Genetic distance, phylogenetic and PCA analyses revealed that Xizang B. rapa possesses extensive genetic diversity and significant genetic differentiation from other B. rapa accessions. By crossing with hexaploid bridge lines (AACCCC), 64 new-type rapeseed lines were developed, demonstrating moderate crossability between hexaploid and B. rapa . Whole-genome resequencing revealed significant genetic divergence of these new-type rapeseed from existing rapeseed cultivars, especially those derived from Xizang B. rapa . This study highlights the rich genetic variation and unique genetic base of Xizang B. rapa , demonstrating its potential to broaden the genetic base of rapeseed and offering valuable insights for future breeding programs. • Xizang B. rapa holds extensive genetic diversity and a unique background, distinctly different from other global B. rapa germplasms. • The crossability of hexaploid bridge lines with diverse B. rapa is governed by the hexaploid parent's genotype. • This hexaploid bridge strategy successfully produced new-type rapeseed lines, most of which are euploid and fertile. • New-type lines, particularly those from Xizang B. rapa , are genetically distinct from natural rapeseed.