| Peanut (Arachis hypogara L.) is important oilseed crop in China. Development of varieties with high oil content is an important goal in peanut breeding program. However, the oil content of peanut varieties released is not very high. This is mainly due to the scarceness in cultivated peanut germlasm with high oil content, not knowing the genetic mechanism of oil content, and difficulty in phenotypic selection because of environmental influence. There are several reports about the high foliar and virus resistance in wild Arachis. But researches on peanut oil content were less. So, it is necessary to detect the oil content of wild species and identify resource with high oil content, develop the molecular makers linked to the oil content and enhance germplasm with high oil content. Association analysis and linkage map of target traits are two methods for molecular marker development. Linkage disequilibrium-based association analysis can be conducted on multiple materials for one consern trait, and it also can be used to analyze multiple characters simultaneously, particularly suitable for quantitative traits, such as oil content. Many studies have showed that homology existed between different wild species. Therefore, natural population constituded by different wild peanut species can be used for association analysis. In this study, wild peanut accessions preserved in the national wild Arachis nursery were used as natural population. The seed oil contents were detected. Polymorphism analysis was conducted through SSR technique. Molecular markers linked to oil content were identified through association analysis. The main results are as follows:1. Eighty-six wild Arachis accessions (including diploid and tetraploid) were tested for oil content and fatty acids by using the method GB/T14488.1-93 and GB/T17377-1998. The minimum, maximum and average value of oil content in wild Arachis were higher than the corresponding value in peanut cultivars. The palmitic acid, stearic acid, arachidic acid and eicosenoic acid content were similar to cultivated peanut. The linoleic acid and behenic acid content were higher and the oleic acid content was lower compared with peanut cultivars. Among the 86 wild relative species, there were 81 accessions with oil content more than 55% and 16 accessions with oil content more than 58%, which accounted for 94.19% and 18.60% respectively. A. appressipila has been found to be the highest oil content (63.74%) in peanut wild germplasm.2. The DNA fingerprint ID of twenty accessions of peanut wild relatives with high oil content (more than 56%) was established. Totally 425 polymorphic bands were produced through the 46 SSR primers. These SSR primers amplified 2 to 21 polymorphic bands with average of 9. Neither single-primer nor double-primer combinations were able to distinguish all the involved accessions. However primer 2E6 of 46 primers and dowble-primer combination 2E6/PM403 could distinguish the 14 and 18 genetypes of the all 20 accessions respectively. Based on the results of three-primer combination detection, five three-primer combinations were able to identify the all 20 accessions involved, including 2E6/PM403/1B9, 2E6/PM403/9A7, 2E6/PM403/10HIA, 2E6/PM403/PM201, 2E6/PM403/PM458, of which 2E6/PM403/10H1A combination was the most efficient. So, the DNA fingerprint ID of the 20 Arachis accessions with high oil content was based on SSR data of the primer combination 2E6/PM403/10H1A, and integrated the accession number and primer name.3. Seventy-nine diploid wild Arachis accessions were used as natural population. Eighty-seven SSR primer pairs with polymorphism were selected from 346 primers to amplify the genomic DNA. Totally 756 polymorphic bands were produced by the 87 primers. Population structure and kinship coefficient were analyzed by software STRUCTURE and SPAGedi. Genetic analysis results showed that the 79 wild species was composed of 2 subpopulations. Kinship analysis results showed that the ratio that kinship﹤0.2 between any two materials were about 75%, reflecting the extensive sources and diversity of wild accessions.4. Sixty-five SSR loci were found to be associated with target traits by using TASSEL2.1 software. Among the 65 loci, seven were found to be associated with oil content, and the phenotype variation explained by them ranged from 0.0218 to 0.0468 and the highest contribution locus was XY-27-1. Two loci were connected with palmitic acid, and the phenotype variation explained by them ranged from 0.0268 to 0.0361. Nine loci were related to oleic acid, and the phenotype variation explained by them ranged from 0.0292 to 0.0543. The highest contribution locus was POCR39-140. Thirteen loci were associated with linoleic acid, and the explained phenotype variation ranged 0.0215 to 0.0609 with the highest contribution locus was POCR39-140. The number of loci that were related to eicosenoic acid was eighteen, and the explained phenotype variation ranged 0.0086 to 0.0438 with the highest contribution locus was POCR39-140. There were eight loci related to behenic acid, and their explained phenotype variation was from 0.017 to 0.0466 with the highest contribution locus was POCR39-140. Another eight loci were found to be connected with tetracosanoic acid, and the phenotype variation explained by them ranged from 0.0063 to 0.0206. The highest contribution locus was XY-89-258. No locus was associated with stearic acid or arachidic acid. The phenotype variation explained by the all 65 loci was from 0.0063 to 0.0609 with an average of 0.0303.5. The phenotypic effects of the 65 alleles were analyzed. Among the alleles that were connected with oil content, five alleles had positive effect and two alleles had negative effects. The alleles XY-27-1 and GI620-234 had the maximum positive effect (+6.24) and XY-2-184 had the maximum negative effect (-0.91). There were only two negative effect alleles related to palmitic acid and the allele with minimum negative effect was PMc660-214 (-0.54). Four positive effect alleles and five negative effect alleles were associated with oleic acid. The maximum positive and negative effect allele was POCR39-140 (+13.67) and XY-2-162 (-13.7) respectively. Seven positive effect alleles (the maximum effect allele was XY-2-162, +12.31) and six negative effect alleles (the maximum effect allele was XY-38-166, -12.31) were connected with linoleic acid. Seven positive effect alleles and eleven negative effect alleles were related to eicosenoic acid. The maximum positive effect allele was XY-95-175 (+1.3) and maximum negative effect alleles were XY-38-166 and 4B11-200 (-1.18). Six positive effect alleles and two negative effect alleles were found to be associated with behenic acid. The maximum positive and negative effect allele was XY-95-175 (+2.37) and POCR39-140 (-2.04). Among the alleles related to tetracosanoic acid, the maximum positive effect alleles were XY-2-162 and XY-89-258 (+1.21), and the maximum negative effect allele was XY-27-5 (-1.22).
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