Interspecific hybridization, polyploidization, and backcross of Brassica oleracea var. alboglabra with B. rapa var. purpurea morphologically recapitulate the evolution of Brassica vegetables.

Xiaohui Zhang,Haiping Wang,Di Shen,Jinglei Wang,Yang Qiu,Mengmeng Duan,Tongjin Liu,Xixiang Li,Jiangping Song

doi:10.1038/srep18618

Abstract

Brassica oleracea and B. rapa are two important vegetable crops. Both are composed of dozens of subspecies encompassing hundreds of varieties and cultivars. Synthetic B. napus with these two plants has been used extensively as a research model for the investigation of allopolyploid evolution. However, the mechanism underlying the explosive evolution of hundreds of varieties of B. oleracea and B. rapa within a short period is poorly understood. In the present study, interspecific hybridization between B. oleracea var. alboglabra and B. rapa var. purpurea was performed. The backcross progeny displayed extensive morphological variation, including some individuals that phenocopied subspecies other than their progenitors. Numerous interesting novel phenotypes and mutants were identified among the backcross progeny. The chromosomal recombination between the A and C genomes and the chromosomal asymmetric segregation were revealed using Simple Sequence Repeats (SSR) markers. These findings provide direct evidence in support of the hypothesis that interspecific hybridization and backcrossing have played roles in the evolution of the vast variety of vegetables among these species and suggest that combination of interspecific hybridization and backcrossing may facilitate the development of new mutants and novel phenotypes for both basic research and the breeding of new vegetable crops.

Highlights

Interspecific hybridization is an important driving force in plant evolution and speciation[1,2,3]
A cytoplasmic male sterile line of B. oleracea var. alboglabra was hand-pollinated with pollen from an inbred line of B. rapa L. var. purpurea
A series of codominant Simple Sequence Repeats (SSR) markers indicated ten of which were derived from B. rapa L. var. purpurea, and nine of which were derived from B. oleracea var. alboglabra (Fig. 1e)

Summary

Introduction

Interspecific hybridization is an important driving force in plant evolution and speciation[1,2,3]. There are two models for the subsequent evolution of plants: genome polyploidization and stabilization, and gene flow with ploidy maintenance[4,5,6,7]. Members of Brassicaceae, a family containing many important vegetable and oil crops, have undergone genomic duplication several times[9]. Crops such as radishes, cabbages, turnips, and Chinese cabbages are diploids. Gongylodes (kohlrabi), B. chinensis (pakchoi), and B. pekinensis (Chinese cabbage) were phenocopied or partially phenocopied in the BC2 plants, providing direct evidence in support of the hypothesis that interspecific hybridization and backcrossing played roles in the evolutionary expansion of vegetable varieties in B. oleracea and B. rapa. Many interesting mutants and previously unknown phenotypes were obtained, indicating that the combination of interspecific hybridization and backcrossing may facilitate the development of more mutants and novel phenotypes

Methods

Results

Conclusion