Germplasm Evaluation And QTL Mapping Of Resistance To Bacteria Strains Of Leaf Pustule And Blight In Soybean Breeding Lines From Yangtze-huai River Valley

Soybean bacterial diseases including bacterial leaf pustule and blight occurred seriously all over the world,and relatively common in north America,China,Brazil,and Argentina.The diseases were epidemic at different level in southern and northern China,and showed a serious trend in Huang-huai-hai region in recent years with some reports in Anhui,Henan,Shandong,Jiangsu,Shanghai.It has been found that developing and growing disease-resistant cultivars is one of the most efficient ways to control disease.It is important to screen and identify resistance resources and understand their genetic base for breeding disease-resistant cultivars.In this thesis,the resistance of a Yangtze-Huai soybean breeding line germplasm population to two strains of bacterial leaf pustule and one strain of leaf blight was evaluated in two years.Association analysis based on MLM_PCA+K model of TASSEL 5.0 software was conducted to detect resistant QTL using available SNP genotypic data.Two related recombinant inbred line populations were also used to map QTL for resistance to the strains of leaf pustule and blight diseases.The main results were as follows:1.Resistance evaluation of the soybean germplasm to bacterial leaf pustule and blight diseaseA YHSBLP population containing 573 lines was used to reveal the genetic variation of resistance to B523,C5 strains of bacterial leaf pustule and S1 strain of leaf blight and to identify elite resistance lines.The results showed that there were significant differences of resistance to three strains in the population,and there was positive correlation between the resistance reaction values to each of the three strains.Forty-three?accounting for 7.5%of whole sample?and 142?24.78%?lines were identified with high and medium resistance levels to B523 strain respectively,and thirty-two?5.58%?and 198?34.55%?lines with high and medium resistance levels to C5 strain were identified respectively.Thirty-three?5.76%?and 140?24.43%?lines were identified with high and medium resistance levels to S1 strain of soybean leaf blight respectively.Total 52 lines were found with high and medium resistance levels to all three strains and 142 lines had resistance to two bacterial strains of the leaf diseases.2.Mapping QTL for resistance to B523,C5 strains of bacterial leaf pustuleSNP markers associated with resistance to B523,C5 strains of soybean bacterial leaf pustule were investigated using the TASSEL5.0 MLM_PCA + K model in YHSBLP population.Under-log10P?4 significance level,57 SNPs were,identified.Among them,29 and 28 SNPs were associated with resistance to B523 and C5 strain respectively.Total 6 and 3 QTL for resistance to these two strains respectively were found on chromosome 4,5,7,8,9 and 17.Among them,2 QTL?qrxp₀5₁,qrxp₁7₁?had the overlap position,and two located?qrxp₁7₁,qrxp₁7₂?on the chromosome region where rxp gene for leaf pustule resistance was found previously.Two recombinant inbred line populations,ZM6 and M6T,were utilized to mapping QTL for resistance to bacterial leaf pustule strains B523 and C5 by Using mixed linear model composite interval mapping?MCIM?method of QTL NETWORK 2.2 software.The results showed that a major QTL,qrxp₁7₁,conferring resistance to both B523 and C5 strains with phenotypic contribution rate of 36.47%-47.29%were detected in ZM6 population.It located between the marker BIN2095 and BIN2097 with physical distance interval 6777393-7362321 bp on Chromosome 17.In M6T population,similar results were also obtained.A QTL qrxp₁7₁ for resistance to B523 and C5 was also mapped on Chr.17 between the marks BIN2924 and BIN2925 with physical distance interval from 7561324bp to 8662563 bp.Its phenotypic contribution rate ranged from 14.69%to 34.07%.The qrxp₁7₁ locus covers the region containing a previously reported resistant gene rxp for bacterial leaf pustule.qrxp₁9₁ with phenotypic contribution rate 5.51%detected in M6T might be a new QTL.3.Mapping QTL for resistance to S1 strain of bacterial leaf blightA genome-wide association study was conducted to reveal the genetic base of resistance to S1 strain of leaf blight using SNP data in the YHSBLP population.Total 9 significant SNPs were detected at the level of-log10P?4,and 3 QTL were found on the chromosome 8,13 and 14.Among them,two loci on chromosome 13 were overlapped with the previously reported Rpg gene for the resistance to leaf blight.Linkage mapping was conducted to reveal the QTL for resistance to S1 strain of bacterial leaf blight in ZM6 and M6T RIL populations.It showed that two QTL,qRpg₁7₁ and qRpg₁9₁,were detected in both population.Other QTL including qRpg₀3₁ and qRpg₁9₂ were also found in M6T population.The position of qRpg₁7₁ is overlapped with that of qrxp₁7₁ which confers resistance to leaf pustule.The results of preliminary candidate gene analysis indicated that there were some resistance-related genes such as zinc finger protein and membrane protein in the region of qRpg₁9₁.