Abstract
Rapeseed (Brassica napus L.) is one of the most important oil crops in the world. However, the yield and quality of rapeseed were largely decreased by clubroot (Plasmodiophora brassicae Woronin). Therefore, it is of great importance for screening more resistant germplasms or genes and improving the resistance to P. brassicae in rapeseed breeding. In this study, a massive resistant identification for a natural global population was conducted in two environments with race/pathotype 4 of P. brassicae which was the most predominant in China, and a wide range of phenotypic variation was found in the population. In addition, a genome-wide association study of 472 accessions for clubroot resistance (CR) was performed with 60K Brassica Infinium SNP arrays for the first time. In total, nine QTLs were detected, seven of which were novel through integrative analysis. Furthermore, additive effects in genetic control of CR in rapeseed among the above loci were found. By bioinformatic analyses, the candidate genes of these loci were predicted, which indicated that TIR-NBS gene family might play an important role in CR. It is believable that the results presented in our study could provide valuable information for understanding the genetic mechanism and molecular regulation of CR.
Highlights
Rapeseed (Brassica napus L., AACC, 2n = 38) is one of the most important and widely cultivated oil crops, which derived from the hybridization of two basic diploid species in U-triangle, Brassica rapa (AA, 2n = 20) and Brassica oleracea (CC, 2n = 18; Nagaharu, 1935)
Physiological Specialization of P. brassicae Played an Important Role in the Genetic Complexity of clubroot resistance (CR)
There has been an abundant of research on characterizing the virulence of P. brassicae (Xue et al, 2008; Cao et al, 2009), and many races have been identified by two identification system (Williams classification and European Clubroot Differential)
Summary
Rapeseed (Brassica napus L., AACC, 2n = 38) is one of the most important and widely cultivated oil crops, which derived from the hybridization of two basic diploid species in U-triangle, Brassica rapa (AA, 2n = 20) and Brassica oleracea (CC, 2n = 18; Nagaharu, 1935). The pathogen could infect about 3,700 species through 330 genera in Brassicaceae (Hwang et al, 2012), among that the host range is most widespread in Brassica, Raphanus, and Arabidopsis (Dixon, 2009). In China, GWAS for Clubroot Resistance race/pathotype 1, 2, 4, 7, 9, 10, 11, and 13, classified on the differentials of Williams, have been identified. The symptoms prevented the root cells from absorption water and nutrition, and caused the host plant malnutrition, growth retardation even death, which resulted in reduction of crop production and quality. Various managements have been used to control the clubroot (KowataDresch and May-De Mio, 2012), improving varieties with durable resistance by classical breeding or genetic modification was still an effective and environment-friendly way
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