Association of Clubroot Resistance Locus PbBa8.1 With a Linkage Drag of High Erucic Acid Content in the Seed of the European Turnip.

Zongxiang Zhan,Zhongyun Piao,Li Zhu,Yingfen Jiang,Bicheng Dun,Zaiyun Li,Zhaoke Hou,Chunyu Zhang,Shisheng Li,Yuanwei Zhou,Nadil Shah

doi:10.3389/fpls.2020.00810

Abstract

Clubroot caused by Plasmodiophora brassicae is a severe threat to the production of Brassica napus, worldwide. The cultivation of resistant varieties is the most efficient and environmentally friendly way to limit disease spread. We developed a highly resistant B. napus line, ZHE226, containing the resistance locus PbBa8.1. However, ZHE226 seeds contain high erucic acid content, which limits its cultivation owing to its low edible oil quality. A segregation population of BC3F2 was developed by crossing ECD04, a resistant European turnip donor, with Huangshuang5, an elite variety with no erucic acid in its seeds, as a recurrent plant. Fine mapping using the bulk segregation analysis sequencing (BSA-Seq) approach detected PbBa8.1 within a 2.9 MB region on chromosome A08. Interestingly, the previously reported resistance gene Crr1a was found in the same region. Genetic analysis revealed that the CAP-134 marker for Crr1a was closely linked with clubroot resistance (CR). Thus, PbBa8.1 and Crr1a might be allelic for CR. Moreover, comparative and genetic analysis showed that high erucic acid in the seeds of ZHE226 was due to linkage drag of fatty acid elongase 1 (FAE1) in the ECD04 line, which was located in the interval of PbBa8.1 with a physical and genetic distance of 729 Kb and 1.86 cm, respectively. Finally, a clubroot-resistant line with a low erucic acid content was successfully developed through gene-specific molecular marker assistant selection from BC4F4. These results will accelerate CR breeding programs in B. napus.

Highlights

Clubroot is caused by a soil-borne, biotrophic obligate pathogen, Plasmodiophora brassicae (Woronin) and is a severe disease of rapeseed (Brassica napus) and other cruciferous crop species worldwide (Dixon, 2009)
A total of 933 BC3F2 individuals derived from ECD04 and Huashuang5 were inoculated with P. brassicae pathotype 4 collected from Huangshan, China
In the early generation of this elite line, the erucic acid content was not determined because it was expected that the offspring should have characteristic low erucic acid content (LEA) and glucosinolate contents

Summary

Introduction

Clubroot is caused by a soil-borne, biotrophic obligate pathogen, Plasmodiophora brassicae (Woronin) and is a severe disease of rapeseed (Brassica napus) and other cruciferous crop species worldwide (Dixon, 2009). The majority of clubroot-resistant germplasm with resistance genes/quantitative trait loci (QTL) were derived from European fodder turnips and were successfully used in CR breeding programs in Chinese cabbage and canola (Diederichsen et al, 2006; Rahman et al, 2011). “Mendel,” originated from a resynthesized B. napus (AACC, 2n = 38) line and was developed through the crossing of Brassica oleracea “ECD15” (CC, 2n = 18) and Brassica rapa “ECD04” (AA, 2n = 20) (Diederichsen and Sacristan, 2010). “Mendel” was successfully crossed with the Canadian spring canola and several lines were developed with high resistance to a number of P. brassicae pathotypes in Canada (Rahman et al, 2014). Crr contains Crr1a and Crr1b, and Crr1a was successfully cloned by Katsunori et al (2013)

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Conclusion