QTL Analysis And Gene Screening Of Drought Tolerance In Brassica Napus L.

Rapeseed is one of the most important oil crops in China,but the drought environment has seriously affected the growth and development,yield and quality of rape.When drought occurs in the rape seedling stage,it will cause the growth of rape seedlings to be blocked or even die;At the flowering stage,the rapeseed production will be greatly reduced.Therefore,breeding high-yielding drought-tolerant varieties is an important breeding goal.In this study,133 F2:8 families constructed by the homozygous lines of Brassica napus 36-Ai(not drought-tolerant)and Kelina-2(stronger tolerant to drought)were used as materials to determine the seedling stage and the initial Fresh weight above ground(SFW),dry weight above ground(SDW),relative leaf water content(RWC),soluble sugar content(SUG)and malondialdehyde content(MDA)after normal irrigation and drought stress at flowering stage;using 6K SNP chips were used to screen SNP sites to construct genetic linkage maps.QTL analysis of drought-tolerant traits and drought-tolerance coefficients was performed.At the same time,the physical intervals of the QTLs located and functional annotations of homologous Arabidopsis genes were used to predict the seedling stage.Candidate genes related to the response to drought stress at the initial flowering stage;finally,the extreme drought-tolerant and non-drought-tolerant families at the seedling stage and the initial flowering stage were screened using population drought tolerance identification data.The main findings are as follows:1.After drought stress,the aboveground fresh weight,aboveground dry weight and leaf relative water content of F2: 8 family population at seedling stage and early flowering period decreased significantly,while the soluble sugar content and malondialdehyde content increased significantly.2.A total of 1074 polymorphic marker sites were detected using 6K SNP molecular marker technology,and a genetic linkage map consisting of 19 chromosomes was constructed with 1041 markers.The total length of the genetic linkage map is2577.03 c M.The average distance between adjacent markers is 2.48 c M.The number of markers located on chromosome A03 is the largest,and the number of markers located on chromosomes C02 and C09 is the least.3.Using the composite interval mapping method,QTL mapping of the five drought-tolerant traits and their drought-tolerant coefficients at the seedling stage and the initial flowering stage:(1)A total of 30 QTLs were detected under normal irrigation and drought stress at seedling stage,of which 12 QTLs were detected under normal irrigation,and the phenotypic variation that could be explained was 7.2%-12.1%;6 QTLs were detected under drought stress,The interpretable phenotypic variation was 7.7%-10.9%;the drought tolerance coefficient detected 12 QTLs,and the interpretable phenotypic variation was 7.7%-14.1%.(2)A total of 11 QTLs were detected under normal irrigation and drought stress at the initial flowering stage,of which 6 QTLs were detected under normal irrigation,and the phenotypic variation that could be explained was 7.7%-9.2%;The interpretable phenotypic variation was 7.0%-7.6%;the drought tolerance coefficient detected 3QTLs,and the interpretable phenotypic variation was 7.0%-9.2%.(3)SDW and RWC detected the same QTL at seedling stage,located on chromosome A09;SFW-DRC and SDW-DRC detected the same QTL,located on chromosome C03.QTLs were detected on the C02 chromosome in both SDW and SUG at the initial flowering stage,and their corresponding physical intervals overlapped.4.A total of 115 candidate genes related to drought were screened in the physical interval of QTL,including 81 at the seedling stage and 34 at the initial flowering stage.There are 19 genes screened together in the two periods,and these 19 genes are located on the C02 chromosome.They mainly affect the expression and signal transduction of drought-tolerant genes,and they mainly encode transport proteins,transcription factors,enzymes,etc.5.Using the membership function method to screen out 5 extreme drought-tolerant families and 5 non-drought-tolerant families at seedling stage and early flowering stage,respectively.