Genetic Mechanisms And Breeding Value Analysis Of Soybean Cyst Nematode Resistance Gene

Soybean Cyst Nematode(SCN, Heterodera glycines Ichinohe) is a devastating disease worldwide in Soybean production. Development of resistant cultivars is the most effective and economical method to control the pathogen. Huang-huai valleys is one of China's major soybean producing areas, where previous research confirmed that Race 1 and 4 are the dominant Races. Therefore, the genetic mechanism of resistance to Race 1 and 4 was deep investigationed ,on this basis, locating QTL of resistant genes and agronomic traits genes, so that high-yield high-quality highly resistant soybean varieties were cultivated. This will be of great significance to soybean production of Huang-huai valleys even the whole country.Soybean variety Essex is the international common disease control, which is sensitive to all the found races.ZDD2315, an excellent resistant source from Shan xi ,has high resistance to Race 1 and 4.Inheritance mechanism of resistance to race 1 and race 4 of SCN was analyzed using different generations, F2, F2:3, BC1F2 and BC1F4 of cross Essex×ZDD2315. Results showed that the resistance to race 1 was controlled with major genes, but without polygenes detected.F2: 3 generation was two pairs of major genes genetic model, and the two had the same additive effects 0.271, and the heritability of major genes were 62.15%;BC1F2 generation was three pairs of major gene genetic model with major gene additive effect 0.293,0.151 and 0.493, respectively, and the heritability of major genes were 72.02%;BC1F4 generation was three pairs of major genes genetic model, and the two of them had the same additive effects 0.402,the other 0.097, and the heritability of major genes were 90.91%.For Race 4, F2 generation was two pairs of major gene genetic model, and the two had major gene additive effect 0.449 and 0.221, respectively, and the heritability of major genes were 65.03%; F2: 3 generation was two pairs of major gene genetic model, and the two had major gene additive effect 0.364 and 0.214, respectively, and the heritability of major genes were 57.81%; BC1F2 generation was three pairs of major gene plus polygene genetic model, and the two of them had the same major gene additive effect 0.125, the other 0.043,and the heritability of major genes were 67.76%, the heritability of polygenes genes were 24.48%; BC1F4 generation was three pairs of major genes genetic model, and the two of them had the same additive effects 0.331,the other 0.205, and the heritability of major genes were 95.91%.Can be seen, the heritability of major genes increased in advanced generations. It could be concluded that selecting resistant lines in advanced generations will be reasonable.QTL mapping was carried out as following. The mapping population with 208 RIL family of the cross Essex×ZDD2315 was established and used to construct a genetic linkage map with 201 SSR markers, spanning 25 linkage groups(LG), each with 3 to 16 markers, at a total distance of 2226 cM, and average marker distance of about 10.8 cM. Based on F8 and F9 generations of phenotypic data, the software Win QTL Cartographer Version 2.5 was used for QTL mapping. CIM (Composite Interval Mapping) method was used to detect a total of 5 QTLs conferring resistance to SCN Race 4,1 plant grains QTL, 2 plant height QTLs, 4 kernel weight QTLs, 6 effective branching QTLs, 7 flowering day QTLs . The two QTLs conferring resistance to SCN Race 4 were located on linkage group G, co-segregated with Sat₁68 and Sat₂10,the two locus could explain 6.4% and 6.0% of the phenotypic variance, respectively. In the N-1 linkage group, the QTL was located between Satt624 and Sat₂75, with the distance between the two markers 6.9cM and 2.2cM, respectively.It could explain 8.2% of the phenotypic variation. In the C2 linkage groups, one was located between Satt658 and Satt316, with the distance between the two markers 21.6 cM and2.6 cM, respectively. It can explain 6.9% of the phenotypic variation; the other was located between Satt316 and Satt307, with the distance between the two markers 3.9 cM and 10.6cM, respectively, it could explain 7.4% of the phenotypic variation. Through two consecutive generations comparison of agronomic traits QTLs showed : The plant height QTL was located in linkage groups A1, co-segregated with Sat₃84,it could explain 10.3% of the phenotypic variation; The two effective branching QTLs were located in linkage groups C2, co-segregated with Satt277 and Satt489, respectively, it could explain 14.6% of the phenotypic variation; The flower day QTL was located in linkage groups C2 between the markers Satt277 and Satt489,it could explain 32.9% of the phenotypic variation.As the resistant source ZDD2315 poor agronomic traits, most allele of the negative yield traits, it is difficult to use it to breed high-yielding, disease-resistant varieties. In this study, it was not detected linkage drag between ZDD2315 agronomic traits and resistant SCN gene .Therefore, high-yielding spread varieties can be used to backcross recurrent parent in breeding. The resistant QTL and the QTL of controlling agronomic traits and yield traits in linkage groups multiple markers were selected at the same time for future generation selection to improve the efficiency of choice and to accelerate the breeding process.