| Many flooding disasters occur frequently due to the heavy rainfall and poor drainage encountered in many areas in the world, and flooding is a common production problem for soybeans [Glycine max (L.) Merr.] in China. Flooding has been recognized in two categories: waterlogging and saturation in soil, waterlogging ulteriorly recognized in small two categories: submergence and incomplete immergence. Soybean is sensitive to flooding and waterlogging stress, especially at early seedling stage as well as flowering and podding stages; On the other hand, there existed great difference in the tolerance to flooding or waterlogging in soybean germplasm, so utilizing tolerant cultivars is one of the most effective ways to improve the soybean production under flooding and waterlogging stresses condition. Identification and discovery of the tolerant germplasm and their target genes is important and basic research work for breeding purposes.Soybean seedling stage is threatened by plum rains in the lower reaches of the Yangzi region. Based on the research of submergence tolerance in soybean, the main objectives of the present study were: (1) to evaluate and identify the submergence tolerance of released cultivar populations from different Asian regions at seedling stage to reveal their genetic variation; (2) to discover the tolerant gene loci and elite alleles to submergence as well as their carriers, and to reveal the cumulative characteristics of elite alleles in the five major pedigrees of Chinese cultivars through association mapping; (3)At the same time, to establish new method system and detect QTLs and linked molecular markers for incomplete immergence tolerance by using RIL population NJRLSX at V2 stage. The main results were as follows.Total 350 accessions sampled from different eco-regions (Huang-Huai Valleys in China, Southern China, East Asia, southeast Asia, and south Asia) were tested for the genetic variation of submergence tolerance. A randomized block design experiment submerged at V0 stage of soybean seedling was carried by using relative death seedling rate(De), relative lost chlorophyll rate(Lo) and relative wilting rate(Wi) as indices and the germplasm which Wangfang has been ascertained as controls . The results included: (1) Lo and Wi correlated significantly with De (P<.0001) , and the indicator system involving De as major index and Lo, Wi as subsidiary indices was effective on the evaluation of submergence tolerance at seedling stage. The De value of Asia released cultivars were 109.8%, higher than that of wild soybeans (104.5%), and nearly equal to that of landrace (110.3%). Cultivars from China existed the highest variation among the different Asian regions, and the De range of Chinese cultivars covered the whole range of the sample population with the value from 4.8% to 212.0%. There existed tolerant variation in all tested regions, and 15 varieties with high tolerant to submergence were identified, i.e. Juxuan23, Nannong493-1, Qiandou2 Hao and so on. Among them, 7 from Huang-Huai, 4 from Southern China, 2 from south Asia, and 1 from East Asia and southeast Asia respectively. The selected tolerant cultivars can be new sources for tolerant breeding, and be compensatory with the tolerant accessions selected from landraces and annual wild soybean.According to the analyses of genetic structure of the total of soybean accessions with 64 simple-sequence repeat (SSR) markers, these experimental materials can be divided into Chinese varieties (Population 1) and exotic varieties (Population 2). This indicated the difference of introduced soybeans breeding direction led to ultimate population genetic structure diversity, so need to study respectively.The Population 1 contained 187 varieties from Huang-Huai valleys and southern China, and was scanned with 85 SSR markers distributed evenly the whole genome. The linkage disequilibrium (LD), population structure and association mapping of QTLs for submergence tolerance as well as the inheritance of the elite alleles in the main pedigree of Population lwere carried out by using Structure 2.2 and TASSEL software. It showed that (1) Population 1 was composed of seven subpopulations, LD was detected extensively (48.63%), and LD decays decreased quickly. (2) Total 14 SSR loci were detected to be associated with three submergence tolerance traits, and some loci associated simultaneously with two or three traits, i.e. Satt681,Satt373,Satt659 and so on, indicating the correlation among these traits. (3) Total 6, 10 and 8 Elite alleles and relative typical carriers of relative death seedling rate and other two traits (Lo and Wi) were also selected. Hedou2 Hao, Qiandou3 Hao, Youbian31 and Nannong493-1 possess more elite alleles. In the five pedigree populations, some elite alleles lost along with breeding cycle change, but others added, which imply the potentials of pyramiding different elite genes to improve the tolerance.Association analysis of 64 SSR markers with the phenotypic data of 3 submergence tolerance traits, 100-seed weight, protein content and fat content was conducted in Population 2 which had 104 accessions from other Asian countries. the results were: (1) Six SSR loci (i.e. Sct033,Satt186,Satt269 and so on) with a total 14 loci were found to be associated with 3 submergence tolerance traits. There also found a certain number of loci associated simultaneously with two or more relative traits. Some loci were consistent with mapped QTLs from family-based linkage mapping procedure. (2) Total 8, 6 and 8 elite alleles of QTLs for submergence tolerance were identified respectively, and three accessions, i.e. PI208432,PI377576, PI481690, with 2 or more than 2 elite alleles were selected.And the 21 SSR loci with a total 29 loci were found to be associated with 100-seed weight, protein content and fat content, some. For the traits of 100-seed weight, protein content and fat content, 6, 8 and 13 elite alleles were identified respectively, and three accessions, i.e. PI175187, PI165926 and PI210351A were selected.RIL population NJRISX from Su88-M21 (tolerant)×Xinyixiaoheidou (Highly sensitive) was evaluated to reveal the genetic base of waterlogging tolerance. The waterlogging stress was kept 5-7 cm water above soil surface for 20 days at V2 stage. It showed: (1) Among the eight traits, the values of plant height increment, the age of leaves and plant height of mature appeared relatively stable and highly correlative, so the mean of values of these traits was used as the indicator to evaluate waterlogging tolerance. (2)The results from segregation analysis under the major gene plus polygene mixed inheritance model showed that waterlogging tolerance of soybean was controlled by two linkage major genes with duplicate effect and polygene detected, the heritability of major genes was 62.83%. (3) QTL mapping for waterlogging tolerance in soybean was carried out under the methods of composite interval mapping (CIM) and multiple interval mapping (MIM) of software Win QTL Cartographer 2.5. There existed transgressive segregation and significant different of lines in the NJRISX population. Two QTLs associated with waterlogging tolerance were identified through both CIM and MIM methods, and both located on linkage group L2 within the regions of Satt229～Satt527 and Satt527～satt286, respectively, explaining 10.1%～25.2% of the total phenotypic variation. With MIM method the other locus on linkage groups L2 was detected which need to be further verified.
|
PDF Full Text Request