Broadening the genetic base of Brassica juncea by introducing genomic components from B. rapa and B. nigra via digenomic allohexaploid bridging

Abstract

A narrow genetic base has hindered improvement of Brassica juncea (AjAjBjBj). In this study, large-scale genomic components were introduced from diploid ancestor species into modern B. juncea using a digenomic hexaploid strategy. The hexaploids AjAjArArBjBj and AjAjBjBjBnBn were first developed from B. juncea × B. rapa (ArAr) and B. juncea × B. nigra (BnBn), and then crossed with dozens of B. nigra and B. rapa, respectively. Both types of hexaploid showed high pollen fertility and moderate seed set throughout the S1 to S3 generations, and could be crossed with diploid progenitor species under field conditions, in particular for the combination of AjAjBjBjBnBn × B. rapa. Thirty AjArBnBj-type and 31 AjArBnBj-type B. juncea resources were generated, of which the AjArBnBj type showed higher fertility. Of these new-type B. juncea resources, 97 individual plants were genotyped with 42 simple sequence repeat markers, together with 16 current B. juncea accessions and 30 hexaploid plants. Based on 180 polymorphic loci, the new-type B. juncea resources and current B. juncea were separated clearly into distinct groups, with large genetic distance between the new-type B. juncea resources and current B. juncea. Our study provides a novel approach to introducing large-scale genomic components from diploid ancestor species into B. juncea.