Study On Heterosis And Genetic Basis Of Soybean

Heterosis is a kind of common phenomenon in biosphere, it is one of the most important approaches increasing crop yield and to improve its quality by the heterosis utility. With the success in development of Three Lines and hybrid breeding, screening of optimized hybridization combination and investigation of the genetic basis have become the work of theoretical and practical importance. The present study was conducted in two trial sites, Jining and Huai'an, both of which were located in Huanghuaihai soybean-producing region. Based on 15 selected parents,50 hybridization combinations were designed by NCII and used for heterosis, parent combining ability and genetic basis studies. The main results were as follows:1. There was significant difference in heterosis among different hybridization combinations. In Jining site, all combinations exhibited positive superiority in 4 traits including yield, per plant pods, seeds per plant, yield per plant. In the other 8 agronomic and qualitative traits, both positive and negative superiorities were observed in different combinations. From the yield standpoint, Yudou 22 x Gaofeng 1, Zhonghuang 13 x Jindou 23, Zhonghuang 13 x Lu 96150, Yudou 22 x Jindou 23, Zhonghuang 13 x Hedou 18, Shanning 16 x Hedou 18, Shanning 16 x Gaofeng 1 were selected as 7 high-yield combinations, with heterobeltiosis rate at 71.10%,78.29%,75.40%,64.36%,66.86%, 65.89% and 70.64%, respectively. The over-standard heterosis rate of these combinations exceeded 52%. In Huai'an site, some of the combinations showed positive superiority while some others showed negative superiority in 12 agronomic and qualitative traits. From the yield standpoint, Huaidou 9 x Nannong 88-31, Xudou 15 x Forrest, Huaidou 4 x Nannong 88-31, Wandou 28 x Plla, Yudou 22 x Jinda 53, Yudou 22 x Nannong 88-31, Xudou 15 x Jinda 53 were selected as 7 high-yield combinations, with heterobeltiosis rate at 30.78%, 33.85%,25.01%,31.59%,32.96%,22.85%and 28.52%, respectively. The over-standard heterosis rate of these combinations exceeded 25%.2. The high combining ability of parents was dependent on the traits. From standpoint of yield, there were 6 parents with high combining ability in Jining site, including Gaofeng 1 (10.25%), Hedou 18 (9.82%), Lu 96150 (7.11%), Jindou 23 (6.28%), Zhonghuang 13 (6.00%) and Yudou 22 (3.79%), and 5 parents with high combining ability in Huai'an site, including Nannong 88-31 (16.32%), Forrest (13.52%), Jinda 53 (9.96%), Jidou 12 (1.33%) and Pella (1.16%), showing a high combining ability.3. In Jining site, the average molecular genetic distance in 15 parents was 0.5709, with the variation ranging from 0.3309 to 0.6691. By Nei & Li similarity coefficient of 0.64 division, these parents can be divided into two groups. Group 1 included Jinda 53, and the other 14 parents were classified as Group 2. Group 2 can be further divided into two subgroups, with one subgroup composed of Ludou 11 and Jindou 23, and the other subgroup composed of Yudou 22, Shanning 15, Shanning 16, Zhonghuang 13, Lindou 9, Xintaohedou, Lu 96150, Ji 4103, Luning 1, Gaofeng 1, Hedou 18, Handou 5. In Huai'an site, the average molecular genetic distance in 15 parents was 0.5694, with the variation ranging from 0.4000 to 0.7076. By Nei & Li similarity coefficient of 0.63 division, these parents can be divided into two groups. Group 1 included Jinda 53, and the other 14 parents were classified as Group 2. Group 2 can be further divided into two subgroups, with one subgroup composed of Jidou 12, Pella, Zhonghuang 39, Forrest, and the other subgroup composed of Huaidou 4, Huaidou 9, Nannong 88-31, Fudou 9675, Hedou 12, Zhonghuang 13, Xudou 15, Wandou 28, Zhoudou 12 and Yudou 22. The foregoing analysis shows, the two proving grounds will Jinda 53 is independently divided into a group, indicating that heredity difference of Jinda 53 was more than other parents.4. The correlation analysis showed that the correlation between SSR genetic distance and heterosis of yield was extremely significant in Jining site. However, there was no significant correlation between SSR genetic distance and heterosis of yield in Huai'an site. These results indicated that prediction of heterosis by using SSR genetic distance relied on the choice of SSR marker and parental materials. To obtain hybridization combination with strong heterosis, there must be enough genetic distance among the parents. Nevertheless, long genetic distance did not necessarily confer a strong heterosis as there were additional factors accountable for determination of heterosis.