Study On Mapping QTL Controlling Bolting And Other Agronomic Traits Of Brassica Campestris

Chinese cabbage (Brassica campestris L.)is one of the most important vegetables in East Asian countries, such as China, Japan and Korea. Early bolting of Chinese cabbage during spring cultivation often has detrimental effects on the yield and quality of the harvested products. Breeding late bolting varieties is a major objective of Chinese cabbage breeding programs.In order to analyze the genetic basis of bolting traits, a genetic map of Brassica campestris was constructed based on AFLP, SRAP, SSR, RAPD, and isozyme markers. Marker analysis was performed on 81 double haploid (DH) lines obtained by microspore culture from F1 progeny of two homozygous parents: BY (an extra-early bolting Chinese cabbage line) and MM (an extra-late bolting European turnip line).In this DH population, distorted segregation is a universal phenomenal. The frequency of distorted segregation markers were high. Out of 432 markers, the number of markers came from male parent and female parent agrees with the Mendel ratio 1:1 approximately. To single marker, the frequency of band from two parents was closely, and not deflected to either parent. It could be concluded that no obvious distorted segregation in the population.A total of 326 markers including 130 AFLPs, 123 SRAPs, 16 SSRs, 43 RAPDs and 14 isozymes were employed to construct a genetic linkage map with 10 linkage groups,which covered a total of 882 cM with an average distance of 2.71 cM between loci. Number of markers in every linkage groups varied from 6 to 118, average interval distance from 1.88 cM to 8.33 cM and the total map distance from 33 to 222 cM. A total of 25.2% deviated markers distributed in the map. The genetic map is fundamental for gene localization, comparative genomics, and QTL mapping of bolting and agronomical traits.The bolting resistance of each DH line were evaluated by bolting index, bolting time and flowering time under controlled conditions. QTL analysis was conducted using MQM mapping with MapQTL5 software. In 2005 and 2006,twenty-one QTL controlling bolting resistance were identified,11 for bolting index, 3 for bolting time, 4 for flowering time. These QTL, accounting for 10.7% to 35% of the phenotypic variation with positive additive effects, were distributed into five linkage groups. BI-5 had the highest contribution to bolting resistance, and it may be a major QTL. These results provide useful information for molecular...