Overcoming Cabbage Crossing Incompatibility by the Development and Application of Self-Compatibility-QTL- Specific Markers and Genome-Wide Background Analysis.

Zhiliang Xiao,Zhiyuan Fang,Honghao Lv,Zhansheng Li,Yumei Liu,Yangyong Zhang,Limei Yang,Mu Zhuang,Yang Hu,Yuqian Xue,Fengqing Han,Yong Wang

doi:10.3389/fpls.2019.00189

Abstract

Cabbage hybrids, which clearly present heterosis vigor, are widely used in agricultural production. We compared two S5 haplotype (Class II) cabbage inbred-lines 87–534 and 94–182: the former is highly SC while the latter is highly SI; sequence analysis of SI-related genes including SCR, SRK, ARC1, THL1, and MLPK indicates the some SNPs in ARC1 and SRK of 87–534; semi-quantitative analysis indicated that the SI-related genes were transcribed normally from DNA to mRNA. To unravel the genetic basis of SC, we performed whole-genome mapping of the quantitative trait loci (QTLs) governing self-compatibility using an F2 population derived from 87–534 × 96–100. Eight QTLs were detected, and high contribution rates (CRs) were observed for three QTLs: qSC7.2 (54.8%), qSC9.1 (14.1%) and qSC5.1 (11.2%). 06–88 (CB201 × 96–100) yielded an excellent hybrid. However, F1 seeds cannot be produced at the anthesis stage because the parents share the same S-haplotype (S57, class I). To overcome crossing incompatibility, we performed rapid introgression of the self-compatibility trait from 87–534 to 96–100 using two self-compatibility-QTL-specific markers, BoID0709 and BoID0992, as well as 36 genome-wide markers that were evenly distributed along nine chromosomes for background analysis in recurrent back-crossing (BC). The transfer process showed that the proportion of recurrent parent genome (PRPG) in BC4F1 was greater than 94%, and the ratio of individual SC plants in BC4F1 reached 100%. The newly created line, which was designated SC96–100 and exhibited both agronomic traits that were similar to those of 96–100 and a compatibility index (CI) greater than 5.0, was successfully used in the production of the commercial hybrid 06–88. The study herein provides new insight into the genetic basis of self-compatibility in cabbage and facilitates cabbage breeding using SC lines in the male-sterile (MS) system.

Highlights

Cabbage (Brassica oleracea L. var. capitata), a cole crop species, is a vegetable of worldwide economic importance due to its strong resistance, wide adaptability, favorable taste and healthcare-related value (Fang, 2000)
Since the late 1990s, breeders have been turning to applying cytoplasmic male-sterile (CMS) or dominant genetic male-sterile (DGMS) lines for cabbage hybrid seed production (Pelletier et al, 1983; Earle et al, 1994; Fang et al, 1997), and many SI lines are still used in the MS system
ARC1, THL1, and MLPK (M-locus protein kinase), which are not associated with the S locus, are involved in pathways related to pollen–stigma interactions

Summary

Introduction

Cabbage (Brassica oleracea L. var. capitata), a cole crop species, is a vegetable of worldwide economic importance due to its strong resistance, wide adaptability, favorable taste and healthcare-related value (Fang, 2000). Pollen genotypes are determined by diploid pollen wall proteins: when the stigma and pollen have the same S-haplotype, they will present an incompatible reaction This system retains genetic variation and avoids inbreeding depression in more than half of angiosperm species. Some studies have shown that genetic variation in S-locus genes may be responsible for self-compatibility, such as SCR (Okamoto et al, 2007), SRK (Gaude et al, 1993; Isokawa et al, 2010), THL1 (Bower et al, 1996), ARC1 (Stone et al, 1999), MLKP (Murase et al, 2004; Hatakeyama et al, 2010). Kakita et al (2007) and Isokawa et al (2010) reported self-compatibility traits that are inconsistent with known S-loci and concluded that new loci may lead to self-compatibility

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Conclusion