Evaluation, Association Mapping Of Soybean Resistance To Common Cutworm And Identification Of Haplotypes In GmAOS1

As an important plant nutrition source, soybean （Glycine max （L.） Merr） provides protein and oil for human and animals. But soybean is also damaged by herbivorous insects. In Nanjing area, leaf-feeding insect is the major problem and common cutworm （CCW, Spodoptera litura Fabricius） is the chief one. CCW belongs to Lepidoptera, Noctuidae, which is a polytrophic pest and need a high feed intake. When the number of CCW is large, the pods in the soybean plant were nearly eaten up. The quality and yield of soybean seed decline because of the damage to soybean plants caused by CCW. Although the application of chemical insecticide could kill pest, the managements also do harm to environment and increase the cost of farmers. Breeding elite soybean cultivars with high levels of plant resistance to insect would reduce the need for chemical pesticide. So soybean insect resistance breeding is an eco-friendly and cost-effective pest management. The screening of soybean germplasm and identification of resistance genes are the basis of soybean pest resistance breeding. So they are important for soybean breeding.In order to screening the soybean germplasm, the insect bioassay was applied to evaluate the resistance of 196 soybean cultivars. Agronomic traits were measured after the leaf-feeding test was complied at V6 growth stage and after the harvest respectively. In the insect bioassay, there were 77 resistant soybean cultivars based on the antibiosis and 107 resistant soybean cultivars based on the antixenosis. In the tolerance test, the 196 soybean cultivars performed different tolerance. The correlation analysis was used to analyze the relationship of the three resistance mechanisms. The result showed that the antibiosis had extremely significant positive correlation with the antixenosis. However, neither the antibiosis nor antixenosis had significant positive correlation with the tolerance. Based on the resistant test, twenty-five elite soybean resistance germplasms were selected, which could be used as new resistant sources in soybean genetics and breeding.Based on the identifications of soybean resistance to CCW,135 genome-wide simple sequence repeat （SSR） markers were used to assess genetic diversity, population structure and linkage disequilibrium （LD） of 196 soybean landraces. Based on the estimated population structure, association mapping for soybean resistance to CCW was conducted using genomic-wide mapping strategies. The elite alleles of soybean resistance to CCW along with their carriers were detected. The result showed that:（1） In addition to widely geographic origin, the population showed extensive genetic variation. （2） In the whole population,17.9% of the SSR pairs were in LD （based on D’>0, P<0.05）; In addition, the extent of LD went further to 6.61 cM as the genetic distance of locus pairs for the loci on the same linkage group （LG）. （3） For association analysis,21 SSRs were associated with soybean resistance to CCW （P<0.005）. Eight of them accounted for>20% of the total genetic variation for resistance. （4） For alleles’effect analysis, the alleles of soybean insect resistance locus major effect on larval weight （LW） of CCW mainly showed positive effect for soybean resistance to CCW （decrease LW of CCW）, and the allele Sat₃34-A208 for largest positive effect （43.9%）. The alleles of soybean insect resistance locus major effect on the leaf consumption of single larva （LCL） mainly showed negative effect for soybean resistance to CCW （increase LCL） and the allele Satt199-A186 for largest negative effect （36.4%）. The alleles of soybean insect resistance locus major effect on pupal weight （PW） of CCW also mainly showed negative effect for soybean resistance to CCW （increase PW of CCW） and the allele Sat₃20-A286 for largest negative effect （31.4%）. The alleles of soybean tolerance locus major effect on I1 mainly showed negative effect for soybean telorance to CCW （decrease the compensation of soybean plant height）, and the allele Satt623-A231 for the largest negative effect （5.2%）. The alleles of soybean tolerance locus major effect on 12 mainly showed positive effect for soybean telorance to CCW （increase the compensation of soybean branch number on main stem）, and the allele Sat₂58-A187 for the largest positive effect （125.9%）. For the alleles of soybean tolerance locus major effect on 13 and 14, the allele Sat₂44-A289 had the largest positive effect for soybean tolerance to CCW,208.8% for 13 and 234.3% for 14 （increase the compensation of seed number and seed weight of single plant）.Based on the SSR markers analysis,1536 SNP developed from expressed sequence tag （EST） were used to identify the soybean resistant genes to CCW by genomic-wide association mapping. Seven SNPs were associated with soybean resistance to CCW based on LW of CCW,11 SNPs associated with soybean resistance to CCW based on LCL, three SNPs associated with soybean resistance to CCW based on PW of CCW, and 16 SNPs associated with soybean tolerance based on compensate indexes. The annotation of genes showed that most of them are function unknown. Tow SNPs which were associated with soybean resistance to CCW based on LW and LCL and located on LG M near the QTL CCW-2 were developed from one Unigene （Gma.867）. The Unigene was annotated as a calcium-responsive transcription co-activator in the NCBI data base.In order to understand the relationship between the diversity of GmAOS1 and the soybean resistance to CCW, the gene were resequenced including the promoter sequence. There were three homologous sequences in the soybean genome. For the three AOS genes, the similarity of nucleotide sequences in coding regions was 79% or more. For sequence polymorphism analysis, there were 43. SNPs or Indels in GmAOS1 sequences among 185 soybean landraces. Forty of them were discovered from promoter sequences. For the promoter sequence,54.9% SNP or Indel pairs were in LD （r2>0, P<0.01）. For haplotype analysis, there were 27 haplotypes in the promoter sequences. For candidate-gene association analysis, GmAOSl were associated with soybean resistance to CCW based on LW,I2,I3 and I4 in 2009.