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A QTL analysis for clubroot resistance (CR) of radish was performed using an F(2) population derived from a crossing of a CR Japanese radish and a clubroot-susceptible (CS) Chinese radish. F(3) plants obtained by selfing of F(2) plants were used for the CR tests. The potted seedlings were inoculated and the symptom was evaluated 6 weeks thereafter. The mean disease indexes of the F(3) plants were used for the phenotype of the F(2). The results of two CR tests were analyzed for the presence of QTL. A linkage map was constructed using AFLP and SSR markers; it spanned 554 cM and contained 18 linkage groups. A CR locus was observed in the top region of linkage group 1 in two tests. Therefore, the present results suggest that a large part of radish CR is controlled by a single gene or closely linked genes in this radish population, although minor effects of other genomic areas cannot be ruled out. The CR locus was named Crs1. Markers linked to Crs1 showed sequence homology to the genomic region of the top of chromosome 3 of Arabidopsis, as in the case of Crr3, a CR locus in Brassica rapa. These markers should be useful for breeding CR cultivars of radish. As Japanese radishes are known to be highly resistant or immune to clubroot, these markers may also be useful in the introgression of this CR gene to Brassica crops.

Genetic factors controlling root shape and red pigmentation on the surface of the hypocotyl (upper part of root) were investigated using a molecular linkage map based on an F 2 population derived from a cross between two radish cultivars, 'Huang-he hong-wan' and 'Utsugi-gensuke'. One hundred and ninety-eight segregating markers (169 AFLPs, 28 Brassica SSRs and one SLG-CAPS) were located on 14 linkage groups (LGs) at a LOD threshold value of 5.0. The mapping position of Brassica SSRs revealed that frequent genomic rearrangements occurred between the Brassica and Raphanus genomes. Three quantitative trait loci (QTLs) for root shape with LOD values of 2.42, 3.22 and 2.88 were identified on LGs 3, 8 and 9, respectively. These three QTLs accounted for 42.4% of the phenotypic variance when joined together. Analysis of QTL(s) for root diameter revealed the presence of two QTLs on LG4 and LG8. The QTL on LG8 was considered to control root thickening and to affect the root shape. For hypocotyl pigmentation, a QTL which exerted a large genetic effect with a LOD value of 9.58, was recognized on LG 11 and accounted for 43.8% of the phenotypic variance.

A segregating doubled haploid (DH) population (n = 96) was developed by anther culture of an F 1 plant crossed between susceptible ('Manganji') and resistant ('Criollo de Morelos 334') lines of pepper (Capsicum annuum L.) to conduct a genetic analysis of resistance to Phytophthora rot caused by Phytophthora capsici. In order to perform a quantitative trait locus (QTL) analysis, we constructed a high density simple sequence repeat (SSR)-based map with a total length of 878 cM. Sixteen linkage groups (LGs) and 118 SSR markers were located using the 626 SSR markers that we previously developed. Resistance was evaluated in two root inoculation tests. Interval mapping for the resistance to P. capsici detected a common major QTL in the duplicate tests and a minor QTL specific to the first test. The major QTL was located on LG15 and flanked with an SSR marker, CAMS420. In addition, seven SSR markers were located within 21 cM intervals from the peak of this QTL. In contrast, the QTL on LG3 was detected with small effects in the first test, the nearest marker was a dominant amplified fragment length polymorphism (AFLP) marker, and the QTL was surrounded by eight SSR markers within a distance of 10 cM. Since some of the linkage markers for agriculturally valuable traits cannot detect polymorphism within breeding populations in C. annuum, the present linkage markers may widen the choice in marker-assisted selection in breeding programs for Phytophthora rot resistant pepper cultivars.

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