Inheritance,Fine Mapping And Marker Assisted Selection Of Resistance Genes To Soybean Mosaic Virus In Soybeans

Soybean mosaic virus （SMV） disease is the major virus disease in soybean （Glycine max （L.） Merr.） worldwide, resulting in substantial yield losses and significant seed-quality deterioration. Breeding resistance varieties is the most economical, effective and environmentally sound approach to control this disease and guarantee a high and stable yield and good quality in soybean production. At present, the identification and distribution of strain groups of SMV in China has been accomplished by Nanjing Agriculture University. In this study, the major prevalent strains （SC3、SC7、SC18、SC15） in soybean production regions domestic were selected to evaluate the resistance of the new cultivars to SMV. Diallel crosses among susceptible cultivar and several resistant cultivars were made to investigate the inheritance of SMV resistance to SC3and to determine the allelic relationship of resistance genes in different resistant cultivars. The resistance gene to SC12was primary mapped and the feasibility of marker-assisted selection （MAS） for RSC12was evaluated by related markers. RSC14Q to SC14was fine mapped via an advanced F2population and the new developed molecular markers. This research supplied some useful information for soybean breeding for disease resistance and provided a foundation for MAS and map-based cloning of resistant genes. The main results were as follows:1. Evaluation of the soybean cultivars resistance to SMV strains SC3, SC7, SC15and SC1813cultivars from the south China tropicalt ecoregion were all inoculated with SMV strain SC18and SC15. The other238cultivars were all inoculated with SC3and SC7.26cultivars were seleceted for their better resistance to SMV. Kefeng No.1, Qihuang No.1, PI96983, PI486355and Kwanggyo were the ones resistant in infection to SMV strains SC3and SC7. Qihuang22, Dabaima, Zaoshul8, Xudou No.1, Davis and Buflla were only resistant in infection to SMV strain SC3.15cultivars including Q0807, Nannong307, Q0806, Zhongzuo056082and so on all showed light symptoms after inoculation of SC3and SC7and their disease index were all within20%, which indicated that they had better resistance in development to SMV strains.The resistance distribution of251cultivars evaluated by weak strains （SC3and SC18） or virulent strains （SC7and SC15） showed that the middle type （middle resistant and middle susceptible） cultivars with a high ratio were more than60%while cultivars in the two ends grades were less than5%. And the cultivars resistant to weak strains were more than to virulent.Soybean resource resistant to SMV is abundant in the provinces of Jing, Lu, Jin in Huang-Huai-Hai ecoregion, where soybean average diseases index was low and variance degree of the resistance among the soybeans is high.2. Studies on inheritance and allelism of resistance genes to SMV strain SC3in soybeansSeven cultivars （Qihuang No.1, Kefeng No.1, Davis, Kwanggyo, Zaoshu18, Xudou No.1and P196983） resistant（R） to SMV strain SC3were crossed respectively with the susceptible（S） cultivar Nannong1138-2to determine the inheritance of their resistance reaction to SC3. As a result, F1from each cross were all resistant to SC3. F2from each cross were all fitted a ratio of3（R）:1（S）, and their separate F2:3lines segregated with a fitness to1（R）:2（segregating）:1（S）. The results showed that a dominant gene controlled the resistance to SC3in each of Qihuang No.1, Kefeng No.1, Davis, Kwanggyo, Zaoshu18, Xudou No.1and PI96983.The R parents were also crossed with each other to evaluate the allelic relationships between the genes in them. There were no susceptible plant in F1and F2from the correspond crosses of Qihuang No.1×Kwanggyo, Qihuang No.1×Zaoshu18, Davis×Kwanggyo, Davis×Zaoshu18, Xudou No.1×Kwanggyo, PI96983×Kwanggyo, which indicated that the single dominant gene with resistance to SC3in Qihuang No.1, Kwanggyo, Zaoshul8, Davis, Xudou No.1and PI96983were allelic at a common locus or very closely linked. F1from the two crosses of Kefeng No.1×Kwanggyo and Kefeng No.1×Zaoshu18were all resistant while their correspond F2population segregated in a ratio of15（R）:1（S）, which indicated that the single dominant gene resistant to SC3in Kefeng No.1and the gene resistant to SC3in each of Kwanggyo and Zaoshul8were not at the same locus and the two different genes inherited independently in their separate hybrid progenies.3. Molecular mapping RSC12and marker assisted selection of resistance genes RSC12and RSC14Q to SMV in soybeanThe P1, P2, F1plants, F2population and F2:3lines from the cross of Qihuang22and Nannong1138-2were all inoculated with the SMV strain SC12for identification of their resistance in the greenhouse. Qihuang22and F1individuals were resistant, and Nannong1138-2were susceptible. F2plants exhibited a good fit to3R:1S, and F2:3lines segregated with an acceptable fitness to1R:2segregating:1S. These results obviously indicated that a single dominant gene, designated as RSC12, controlled resistance to SC12in Qihuang22.A F2population of Qihuang22（R） XNannong1138-2（S） with219individuals was constructed for molecular mapping of resistance gene RSC12to SMV in soybean. Linkage analysis between inoculation phenotype and genetic markers by using the software MAPMAKER/EXP3.0b demonstrated that the resistance gene Rsc12was located on the linkage group F and linked with seven SSR markers. The order and genetic distance linked RSC12were Sat₂976.4cM Sat₂344.9cM Sat₁541.1cM Satt1140.7cM SOYHSP1761.6cM Satt3342.4cM RSC126.3cM Sct₀33.The MAS efficiency of SSR markers Satt334and Sct₀33for Rsc12and RSC14Q was evaluated in F2, F3and F4populations from Qihuang22XNannong1138-2and F5, F6populations from Qihuang No.1XNannong1138-2. The results indicated that the MAS efficiency of Satt334and Sct₀33for RSC12or RsSC14Q was more than85%, and that the MAS efficiency reached as high as95%when these two markers were co-used. Therefore, the two SSR markers can be used effectively in selecting for resistance genes RSC12and RSC14Q to SMV instead of inoculation identification4. Fine mapping of resistance gene RSC14Q to SMVBased on the primary mapping of RSC14Q on the linkage group F （Li et al,2006）,4residual heterozygous lines （RHLs） which have a heterozygous aim segment and a homozygous genetic background were screened from a recombinant inbred line （RIL） of soybean. The RILs were obtained from a cross between Qihuang No.1（R） and Nannong1138-2（S）. The advanced F2population with680individuals constructed by selfing of4RHLs （F8） could be used for fine mapping of RSC147Q since its segregation ratio fitted to3R:1S after phenotype identification.Based on the physical position of RSC14Q region, two InDel markers （MY750and MY26530） and one SNP marker （MY525） were newly developed by re-sequencing PCR products using primers designed from the soybean genome sequence. The new markers obtained to saturate the genetic map of target gene were helpful to fine map RSC14Q·By linkage analysis between inoculation phenotype and genetic markers, RSC14Q was located at interval between Sart334and MY750, with genetic distance of0.6cM and0.5cM, respectively, which corresponded to a physical distance on the Williams82draft assembly （Glyma1.13） of1.18Mb. And then according to the genetic analysis and recombination information of the two individuals and their separate F2:3lines, RSC14Q was concluded to be located at a narrower interval between MY525and MY750. Thus the genomic region containing RSC14Q was further confined to616kb interval based on the soybean genome information. These results provided a foundation for MAS and map-based cloning of RSC14Q·...