Novel glucosinolate composition lacking 4-methylthio-3-butenyl glucosinolate in Japanese white radish (Raphanus sativus L.).

KEY MESSAGE: Genetic analysis and gene mapping of the 4-methylthio-3-butenyl glucosinolate-less trait of white radish were performed and a white radish cultivar with new glucosinolate composition was developed. A spontaneous mutant having significantly low 4-methylthio-3-butenyl glucosinolate (4MTB-GSL) content was identified from a landrace of Japanese white radish (Raphanus sativus L.) through intensive evaluation of glucosinolate profiles of 632 lines including genetic resources and commercial cultivars using high-performance liquid chromatography (HPLC) analysis. A line lacking 4MTB-GSL was developed using the selected mutant as a gene source. Genetic analyses of F1, F2, and BC1F1 populations of this line suggested that the 4MTB-GSL-less trait is controlled by a single recessive allele. Using SNP and SCAR markers, 96 F2 plants were genotyped, and a linkage map having nine linkage groups with a total map distance of 808.3 cM was constructed. A gene responsible for the 4MTB-GSL-less trait was mapped between CL1753 and CL5895 at the end of linkage group 1. The genetic distance between these markers was 4.2 cM. By selfing and selection of plants lacking 4MTB-GSL, a new cultivar, 'Daikon parental line No. 5', was successfully developed. This cultivar was characterized by glucoerucin, which accounted for more than 90% of the total glucosinolates (GSLs). The total GSL content in roots was ca. 12 µmol/g DW, significantly lower than those in common white radish cultivars. Significance of this line in radish breeding is discussed.

Mapping of quantitative trait loci for high level of self-incompatibility in Brassica rapa L.

The level of self-incompatibility (SI) is important to the purity of F1 seeds produced using the SI system of Brassica vegetables. To analyze the genetic basis of the level of SI, we generated an F2 population derived from a cross between a turnip inbred line showing a high level of SI and a Chinese cabbage inbred line showing a low level, and evaluated the level of SI under insect pollination in two years. We constructed a detailed linkage map of Brassica rapa from the F2 progeny, consisting of SSR, SNP, indel, and CAPS loci segregating into 10 linkage groups covering approximately 700 cM. Five quantitative trait loci (QTL) for high-level SI were identified. The phenotypic variation explained by the QTL ranged between 7.2% and 23.8%. Two QTL were detected in both years. Mapping of SI-related genes revealed that these QTL were co-localized with SLG on R07 and MLPK on R03. This is the first report of QTL for high-level SI evaluated under insect pollination in a Brassica vegetable. Our results could be useful for the marker-assisted selection of parental lines with a stable SI.