Study on the application of DNA markers to breeding and identification of cultivar diversity in carnation

This study was carried out to utilize DNA markers in carnation (Dianthus caryophyllus L.) breeding and to clarify the genetic basis such as the ploidy level and genetic diversity of carnation cultivars. 1. Construction of genetic linkage map, quantitative trait locus (QTL) analysis and application to breeding in carnation. To improve the selection efficiency in carnation breeding for resistance to bacterial wilt caused by Burkholderia caryophylli, the first genetic linkage map for the carnation was constructed by using a resistance-segregating population of 134 progeny lines derived from a cross between 'Carnation Nou No. 1' (a line resistant to bacterial wilt) and 'Pretty Favvare' (a susceptible cultivar) based on RAPD and SSR analysis. The linkage map contained 137 RAPD and 9 SSR markers. Linkage analysis revealed that 124 loci could be mapped to 16 linkage groups that extended for 605.0 cM. The average interval between two loci was 4.9 cM. QTL analysis was applied to replication 8 evaluations of resistance to bacterial wilt. A QTL with a large resistance effect was detected on Group 6, which accounted for 60.5% of the total phenotypic variance with an LOD score of 23.46. Two other QTL with a small effect were detected on Groups 2 and 5 with LOD scores of 2.32 and 2.87, respectively. These results suggest that resistance to bacterial wilt in carnation is related to one major and at least two minor genes. The availability of marker-assisted selection (MAS) using DNA markers close to the QTL of resistance to bacterial wilt in carnation was examined. The STS-WG44 marker tightly linked to the major resistance gene was detected in all backcross lines with resistance selected by the root-soaking method. The ratio of markers OQ12 and STS-WB66 close to the two QTL with a small effect in resistant lines was lower in succeeding generations of backcrossing. These findings suggest that STS-WG44 is available for selecting resistant lines. In practical breeding populations, the difference in mean disease incidence between two groups categorized as having or lacking STS-WG44 was 62.6% and STS-WG44 was present in most lines showing disease incidence of less than 20%. These findings suggest that STS-WG44 as a selective marker facilitated the narrowing of populations to those that are highly resistant for practical breeding. MAS would be available for breeding improved resistance to bacterial wilt in carnation. Flower color is an important trait in ornamental plants. To understand the genetic basis for anthocyanin pigmentation traits in the flower petals of carnation, the segregation of anthocyanin content in petals was evaluated and QTL analysis was conducted by using the linkage map constructed in this study. The frequency of low anthocyanin content (0.5 mg/g FW.) was highest and the frequency decreased in inverse proportion to anthocyanin content. QTL analysis identified two QTL on linkage Groups 6 and 9, which accounted for 21.6% and 15.0% of the total phenotypic variance, with LOD scores of 6.33 and 4.15, respectively.