Abstract
European fodder turnips (Brassica rapa ssp. rapifera) were identified as sources of clubroot resistance (CR) and have been widely used in Brassica resistance breeding. An F2 population derived from a cross between a resistant turnip and a susceptible Chinese cabbage was used to determine the inheritance and locating the resistance Quantitative Trait Loci (QTLs). The parents showed to be very resistant/susceptible to the field isolates (pathotype 4) of clubroot from Henan in China. After inoculation, 27 very resistant or susceptible individuals were selected to construct bulks, respectively. Next-generation-sequencing-based Bulk Segregant Analysis Sequencing (BSA-Seq) was used and located resistance QTL on chromosome A03 (3.3–7.5 Mb) and A08 (0.01–6.5 Mb), named Bcr1 and Bcr2, respectively. Furthermore, an F3 population including 180 families derived from F2 individuals was phenotyped and used to verify and narrow candidate regions. Ten and seven Kompetitive Allele-Specific PCR (KASP) markers narrowed the target regions to 4.3–4.78 Mb (A03) and 0.02–0.79 Mb (A08), respectively. The phenotypic variation explained (PVE) of the two QTLs were 33.3% and 13.3% respectively. The two candidate regions contained 99 and 109 genes. In the A03 candidate region, there were three candidate R genes, namely Bra006630, Bra006631 and Bra006632. In the A08 candidate region, there were two candidate R genes, namely Bra030815 and Bra030846.
Highlights
Clubroot caused by Plasmodiophora brassicae Woronin has become one of most serious diseases of cruciferous crops worldwide [1]
An F2 population derived from a cross between a resistant turnip and a susceptible Chinese cabbage was used to identify resistance QTL
Bcr2 explained 13.3% of the phenotypic variation of resistant to clubroot (Figure 6)
Summary
Clubroot caused by Plasmodiophora brassicae Woronin has become one of most serious diseases of cruciferous crops worldwide [1]. The pathogen causes the formation of galls on the roots of susceptible plants and leads to stunted growth, wilting and premature chlorosis of the aboveground plant organs, leading to yield and quality losses. In China, clubroot was identified as an important quarantine target in the first National Plant Quarantine Conference in 1953. It is distributed across most regions of the country at present [4]. P. brassicae is known to consist of numerous races. The differential system of Williams [5] is most commonly used to determine the races into 16, such as pathotypes 1 to 16
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