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

Zili Wei,Jinling Meng,Meng Wang,Peifa Liu,Jun Zou,Chao Wu,Shihao Chang

doi:10.3389/fpls.2016.01677

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.

Highlights

Brassica juncea (AjAjBjBj, 2n = 36) is a tetraploid that originated from its diploid progenitors, B. rapa (ArAr, 2n = 20) and B. nigra (BnBn, 2n = 16)
A set of Brassica allohexaploids in which the Ar and Bc subgenomes of B. carinata (BcBcCcCc) and B. rapa (ArAr) (Tian et al, 2010) were combined was used as donors for the introgression of exotic subgenomes into the traditional B. juncea genome
To broaden the genetic base of traditional B. juncea, we demonstrated an approach to generate new-type B. juncea lines with introgression of subgenomes from its related oilseed species, B. rapa and B. carinata, via interspecific crossing and intensive selection

Summary

Introduction

Increasing attention is being paid to B. juncea worldwide, given its unique and favorable traits, such as resistance to biotic and abiotic stress and a low rate of pod shattering These traits are desirable in the context of global climate change given its capacity to adapt to heat and other stresses that are commonly encountered under field conditions in Canada, Australia, and many other parts of the world (Woods et al, 1991; Cheung et al, 1997; Burton et al, 2004; Huangfu et al, 2009; Amanullah et al, 2011; Chen et al, 2013). The low seed yield of B. juncea in most of the rapeseed growing area substantially restricts extensive planting of this species worldwide This is largely due to deleterious changes in its genome from genetic improvement programs and the absence of a novel approach to exploit the benefits associated with heterosis, and an international effort is needed to genetically improve this crop (Pradhan and Pental, 2011). Increasing the seed yield, exploring novel germplasms, and promoting new approaches for hybrid breeding are essential for improving the agricultural production of B. juncea

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