Introgressing Subgenome Components from Brassica rapa and B. carinata to B. juncea for Broadening Its Genetic Base and Exploring Intersubgenomic Heterosis

Abstract

Brassica juncea (AjAjBjBj), is an allotetraploid that arose from two diploid species, B. rapa (ArAr) and B. nigra (BnBn). It is an old oilseed crop with unique favorable traits, but the genetic improvement on this species is limited. We developed an approach to broaden its genetic base within several generations by intensive selection. The Ar subgenome from the Asian oil crop B. rapa (ArAr) and the Bc subgenome from the African oil crop B. carinata (BcBcCcCc) were combined in a synthesized allohexaploid (ArArBcBcCcCc), which was crossed with traditional B. juncea to generate pentaploid F1 hybrids (ArAjBcBjCc), with subsequent self-pollination to obtain newly synthesized B. juncea (Ar/jAr/jBc/jBc/j). After intensive cytological screening and phenotypic selection of fertility and agronomic traits, a population of new-type B. juncea was obtained and was found to be genetically stable at the F6 generation. The new-type B. juncea possesses good fertility and rich genetic diversity and is distinctly divergent but not isolated from traditional B. juncea, as revealed by population genetic analysis with molecular markers. More than half of its genome was modified, showing exotic introgression and novel variation. In addition to the improvement in some traits of the new-type B. juncea lines, a considerable potential for heterosis was observed in inter-subgenomic hybrids between new-type B. juncea lines and traditional B. juncea accessions. The new-type B. juncea exhibited a stable chromosome number and a novel genome composition through multiple generations, providing insight into how to significantly broaden the genetic base of crops with subgenome introgression from their related species and the potential of exploring inter-subgenomic heterosis for hybrid breeding.

Heterotic patterns of primary and secondary metabolites in the oilseed crop Brassica juncea

“…The importance of B. juncea as an oilseed crop is growing globally due to its unique and favorable traits, such as resistance to biotic and abiotic stresses and low rate of pod shattering. Prior efforts have significantly increased the seed yield and quality traits (Augustine et al 2014;Wei et al 2016) but more genetic improvement is necessary (Grover and Pental 2003).…”

Investigation of the Genetic Diversity and Quantitative Trait Loci Accounting for Important Agronomic and Seed Quality Traits in Brassica carinata

“…It consists of the two homologous genomes, B and C, and may have originated as an allotetraploid species as a result of spontaneous hybridization between diploid species; Brassica nigra (2 n = 2 x = 14, genome BB) and Brassica oleracea (2 n = 2 x = 18, genome CC) in Ethiopia (Nagaharu, 1935; Lukens et al, 2004; Warwick, 2011). B. carinata harbors useful genes for resistance to abiotic and biotic stresses (Getinet et al, 1996), and therefore has been used as a donor for introgression of genes to improve and widen the gene pool of Brassica rapa, Brassica napus , and Brassica juncea germplasm (Meng et al, 1998; Xiao et al, 2010; Wei et al, 2016). …”

Reconstituting the genome of a young allopolyploid crop, Brassica napus, with its related species

“…Previous research showed that intersubgenomic hybrids derived from crosses between natural lines and genomereplaced/resynthesized lines offer a substantial heterosis potential in B. napus and Brassica juncea (Fu et al, 2012;Gupta et al, 2015;Wei et al, 2016;Zou et al, 2010). The RS subpopulation of the gene pool apparently differed from the traditional B. napus subpopulation, and they were grouped into two different genetic clusters with a larger genetic distance between the lines of the RS subpopulation and traditional B. napus than that within the traditional B. napus subpopulation.…”