Molecular Genetic Map Construction And QTL Mapping Of Main Agronomic Traits In Flowering Chinese Cabbage

Flowering Chinese cabbage is one of the largest cultivated vegetables in southern China.Superior quality,high yield and stress resistance are the major targets in the breeding program of flowering Chinese cabbage breeding.With the development of molecular marker technology,genetic map construction and quantitative trait locus(QTL)mapping have become an important part of study and application in crop genetics and molecular marker-assisted selection breeding.The application of markers linked to QTLs can accelerate the process in the breeding program.In this study,a genetic map of flowering Chinese cabbage covering 10 linkage groups was constructed by using simple sequence repeat(SSR)markers and 130 recombinant inbred lines(RIL)from the cross “3T6” and “Sijiu-19caixin”.Based on phenotypic data of the main agronomic traits in 133 RILs,QTL analysis for the main agronomic traits was performed.The results are as follows:Through the usability screening of 790 SSRs developed from transcriptome sequencing of flowering Chinese cabbage and 160 SSRs selected from multinational Brassica genome project database,212 SSRs whose PCR products were clear,reproducible and polymorphic in the parents of “3T6” and “Sijiu-19caixin” were obtained,and 283 allelic variants were detected by genotyping of RIL populations with these polymorphic SSRs.According to the data of allelic variants in flowering Chiness cabbage RIL population,a genetic map covered 1723.81 cM with 10 linkage groups was constructed in flowering Chiness cabbage by using the MapMaker 2.0 software.The genetic map contained 197 allelic variations and with an average distance of 8.75 cM in two loci.According to the chromosomal locations of Brassica SSRs used in the study,the corresponding chromosomes for the 10 constructed linkage groups were confirmed.In addition,114 of 197 allelic loci in the genetic map showed segregation distortion.Among of them,of 75 biased to male parent "3T6",accounting for 65.79%of all the segregation distortion loci;of 39 biased to female parent "Sijiu-19caixin",and accounting for 34.21% of all the segregation distortion loci.The 17 segregation distortion regions(SDR)were found on the 9 chromosomes.Among of them,chromosome A10 contained 3 SDRs;A1,A2,A3,A5,A7 and A9 chromosomes had 2SDR each,while A6 and A8 chromosomes comprised only 1 SDR each.On the basis of the constructed genetic map and the phenotyping data determined in two years' experiments for the main agronomic traits of plant height,plant diameter,plant weight,stalk height,stalk diameter,stalk weight,length of the largest leaf,width of the largest leaf,petiole length of the largest leaf,petiole width of the largest leaf,basal leaf number,stem leaf number and chlorophyll content-related SPAD value,QTL mapping was carried out by using QGene 2.30 software.A total of 29 QTLs were identified with 8.5-30.3% of phenotypic variance explained by QTLs.These QTLs were located in chromosomes A1,A4,A5,A6,A7,A8,A9 and A10.Among of them,the maximum number of QTLs related to the width of the largest leaf was 5,followed by SPAD value with 4 QTLs;the number of QTL for each of the length of the largest leaf and stem weight was 3;and the number of QTL relates to each of plant diameter,petiole length,petiole width,stalk diameter and plant weigh was 2;plant height,basal leaf number,stem leaf number,stalk height were only 1 QTL each.In addition,plant weight,length of the largest leaf and width of the largest leaf contained an individual QTL which was reproducible in two years' experiemts with more than10% of explaination rate of phenotypic varience.These results could provide reference for marker-assisted selection in the breeding program of flowering Chinese cabbage.