Genetic Variability, QTL Mapping And Elite Allele Identification Of Oil Traits In Cultivated And Wild Soybean Germplasm In China

Soybean [Glycine max （L.） Merr.] is one of the most important vegetable oil crops in the world. It has various industrial uses and domestic food applications. The quality of soybean oil depends greatly upon its fatty acid composition. The breeding on oil related traits is one of the important targets in soybean breeding. It is important to study the variation and QTL mapping of oil related traits. In present study,1417 accessions characteristic in different eco-regions and variation were studied and some elite accessions were selected from the 1417 accessions. Additive and epistatic QTL mapping were done in NJRIKY population using three mapping procedures with replicated tests in three years. Association mapping was done in 165 wild soybeans,364 landraces and 178 released cultivars with 108 SSR markers, and the allele structure of elite materials was discussed. The main results were as follows:1. Genetic variability of oil related traits in soybean germplasm in China（1） In general region, the oil content of released and landrace soybeans were 18.98% and 17.55%, which was about 7% more than that of wild soybean. The coefficient of variation was decreased from wild soybean to released soybean. The oleic acid content of wild soybean was 14.92%, and that was 22.26% in landrace and 26.23% in released soybean. The oleic acid content and coefficient of variation were both increased from wild soybean to released soybean. The linoleic acid content of wild soybean was 55.90%, which was higher than that of in landrace 54.44% and released soybean 51.52%. But the coefficient of variation in wild soybean was lower than that of in landrace and released soybean. The linolenic content acid content was 13.21% in wild soybean, which was higher than 8.59% in landrace and 7.31% in released soybean. The coefficient of variation in wild soybean was also higher than that of in landrace and released soybean. The differences of saturated fatty acid content and coefficient of variation were not significant in three populations.（2） The range and means of oil content in wild soybean, landrace and released soybean in different eco-regions were as follows:I:7.51-20.68 （11.28）,11.54-24.89 （19.33） and 16.74-22.80 （20.20）; â…¡:74-19.26 （12.99）,12.87-22.85 （18.29） and 14.24-24.34 （19.93）; â…¢: 9.70-18.43 （12.71）,12.73-23.65 （17.70） and 16.13-20.97 （18.84）; â…£:7.62-18.67 （11.85）, 12.96-22.78 （16.66） and 16.06-21.05 （18.53）; V:9.01-15.25 （11.27）,13.94-20.59 （16.72） and 16.90-22.03 （19.05）; â…¥.81-22.40 （16.57） and 15.85-19.14 （17.32） （There was no wild soybean in VI）. It indicated that the variation of oil content between regions varied greatly with abundant variation within regions. The variation of oleic acid, linoleic acid and linolenic acid were similar to that of oil content. The range and means of palmitic acid content in wild soybean, landrace and released soybean in different eco-regions were as follows:â… :11.47-15.01 （13.02）,9.30-12.95 （11.35） and 9.53-12.93 （11.20）; â…¡:11.14-14.46 （12.57）,9.18-13.21 （11.44） and å’Œ 9.68-13.66 （11.31）; â…¢:10.66-14.41 （12.54）,7.94-16.22 （11.04） and 9.56-12.40 （11.01）; â…£:9.47-14.67 （12.05）,8.93-13.42 （10.98） and 9.08-12.96 （10.94）; â…¤:11.87-13.79 （12.81）,9.82-12.49 （11.34） and 10.19-12.08 （11.20）; â…¥: 9.50-12.58 （11.24） and 11.56-12.76 （12.17）. It indicated that the variation of palmitic acid content between regions varied little with abundant variation within regions. The variation of stearic acid was similar to that of palmitic acid content.The correlation analysis between oil related traits content and latitudes was studied. Palmitic acid and stearic acid were observed positive correlation in wild soybean with r=0.34** and 0.22**. Oil, oleic acid and palmitic acid were observed the positive correlation in landrace soybean with r=0.44**,0.31** and 0.12**. Linoleic acid and linolenic acid were observed the negative correlation in landrace soybean with r=-0.25** and-0.43**. Oil, linoleic acid, linolenic acid and stearic acid were observed the positive correlation with r=0.46**,0.25**,0.38** and 0.12*. Oleic acid was negative correlation with r=-0.26**. It indicated that the artifical selection produced correlation between oil related traits and latitudes that had no obvious original correlation, which was consistent with the result of Zheng et al （2006）.（3） Baesd on Zheng et al （2006） and Liu et al （2008）, some new elite germplasm were selected based on the content more than 23% for oil,40% for oleic acid,60% for linoleic acid and below 5% for linolenic acid. For example, N9119.1, N25301 and N24192 with >23% oil content, N25450 with 48.28% oleic acid content and N23839 with 45.01% oleic acid content and 4.85% linolenic acid content, those materials can be used in breeding.2. Mapping additive and epistatic QTLs of oil content and fatty acid components in NJRIKY population（4） In NJRIKY population, all the tested traits showed transgressive segregation, indicating the complementary genetic structure between the parents. QTLNetwork2.0 software was used to detect QTLs and WinQTLCart2.5 and QTL IciMapping2.0 were used to check and verify the obtained results. A total of 27 additive QTLs and 18 pairs of epistatic QTLs were detected. The remnant part of genetic variance minus additive and epistatic variance was defined as the undetected minor QTLs. For oil content, three additive QTLs and two pairs of epistatic QTLs were detected with the total additive effect accounting for 15.63% and total epistatic effect accounting for 10.79% of the phenotypic variance, and 49.99% undetected minor QTLs. For oleic, linoleic, linolenic, palmitic and stearic contents, the total contributions of additive QTLs were 10.35%（3 QTLs）,11.70%（3）,28.54%（7）,27.00%（6） and 29.61%（5）, and those of the epistatic QTLs were 10.23%（3 pairs of QTLs）,8.50%（2）, 7.54%（3）,16.59%（7） and 4.31%（1）, respectively. The total contributions of the undected minor QTLs were 61.63%,56.05%,53.15%,48.86% and 54.95%. Two QTLs for linoleic acid content showed QTL×year interaction with total contribution 5.45%. The accumulated contribution of additive QTLs and that of epistatic QTLs were nearly equal in oil, oleic, linoleic and palmitic content, indicating the importance of both additive and epistasis effect for the traits. A considerably large part of undetected minor QTLs was observed in all traits. Accordingly, in breeding for oil and fatty acid contents, the strategy of pyramiding multiple QTLs, both additive and epistatic, by using marker-assisted selection combined with accumulating minor effect QTLs through conversional procedures should be considered since very few QTLs with contribution rate more than 10% have been detected.3. Association analysis of oil related traits in cultivated and wild soybean（5） 707 soybean accessions were divided into three subpopulations, which was consistented with three types of germplasm.17.32% linkage desequilibrium loci pairs with D’0.5～0.8 loci pairs 10.91% and D’ value 0.40 were observed in wild soybean.32.64% linkage desequilibrium loci pairs with D’0.5-0.8 loci pairs 2.86% and D’ value 0.33 were observed in released soybean.16.15% linkage desequilibrium loci pairs with D’0.5-0.8 loci pairs 1.18% and D’value 0.31 were observed in released soybean. It indicated that there were more linkage desequilibrium loci pairs with low degree than that of in wind soybean. The consesquece of linkage desequilibrium landrace soybean was similar to that of in released soybean.38 marker loci were detected in association analysis with the tatal 46 loci （times）. Seven, eight, six, thirteen, five and seven loci were associated with oil, oleic, linoleic, linolenic, palmitic and stearic content. Four, one, one, two, zero and two QTLs were in agreement with mapped QTLs from family-based linkage mapping procedure. Six loci were associated with oleic and linoleic content simultaneously, which may be the genetic basis of phenotypic correlation.（6） Positive and negative effect allele and their phenotypic effects were analyzed. Each loci had 6～47 alleles. The loci gmes3058a associated with oil, oleic acid and linolenic acid had 6 alleles. The loci Satt277 associated with linolenic acid had 47 alleles. Among 7 loci associted oil content, each loci had 6～36 alleles. The range of maximal negative effect was-4.98%～-8.95% and that of positive effect was+2.98～+5.53%（Satt311-202）. Among 8 loci associted oleic acid content, each loci had 6-40 alleles. The range of maximal negative effect was -4.52%～-9.25% and that of positive effect was+6.42%～+15.05% （Sat₂89-384）. Among 6 loci associted linoleic acid content, each loci had 16-40 alleles. The range of maximal negative effect was -4.73%～-10.54% and that of positive effect was +2.03%～+6.58%（Sat₂99-404）. Among 13 loci associted linolenic acid content, each loci had 6-47 alleles. The range of maximal negative effect was -2.27%～-3.21% （Satt509-264） and that of positive effect was+2.05%～+6.65%. Among 5 loci associted palmitic acid content, each loci had 8～38 alleles. The range of maximal negative effect was -0.33%～-1.33%（Sat₃37-317） and that of positive effect was+1.11%～+1.99%. Among 7 loci associted stearic acid content, each loci had 7-31 alleles. The range of maximal negative effect was -0.23%～-0.96%（Sct₁90-245） and that of positive effects was+0.07%～+1.01%.（7） The total allele in wild soybean, landrac and released soybean were respectively 1223,1112 and 638 with average allele in each accsssion 11.3,10.3 and 5.9, which indicated that the genetic diversity was decreased from wild soybean to released soybean. There were 100,79 and 39 alleles at 7 loci associated oil content with 93,2010 and 1211 positive effect alleles in wild soybean, landrace and released soybean. Average positive effect alleles in each accession were 0.6,5.5 and 6.8. The oil content was increased from wild soybean to released soybean. All of above indicated that positive effect alleles were important to the increasing of oil content. Baed on 10 elite accessions in wild soybean, landrace and released soybean,1,34 and 55 elite alleles were detected, which indicated that elite alleles were important to the increasing of oil content. The consequences of oleic acid, linoleic acid and linolenic acid were similar to the oil.（8） The elite allele distributions of oil, oleic acid and linolenic acid were analyzed. The common elite alleles in 58-161, Xu dou 1 hao, Qi huang 1 hao, Nan nong 1138-2 and Nan nong 493-1 were respectively gmes3041-278, gmes3058a-265 and gmes3058a-265 in oil, oleic acid and linolenic acid. Each accession had elite alleles and there were 3-7,1-7 and 5-12 elite alleles in wild soyean, landrace and released soybean respectively. Most of elite accessions had more elite alleles, which indicated the importance of elite alleles for the elite accessions.