Inheritance And Gene Tagging Of Male Fertility Restoration Of Cytoplasmic-Nuclear Male Sterile Line NJCMS2A In Soybean

Utilization of heterosis is an effective way to increase crop yields. Cytoplasmic-nuclear male sterility plays an important role in the production of hybrid seeds. The knowledge of inheritance of male fertility restoration of a cytoplasmic-nuclear male-sterile line is essential to hybrid seed production. With the rapid development of molecular markers, mapping male fertility restoration genes appears an effective way to study inheritance of the trait. The soybean cytoplasmic-nuclear male-sterile line NJCMS2A was developed through consecutive backcross procedures with the F₂ male sterile plants of the (N8855×N1628) cross as donor parent and N1628 (designated as NJCMS2B afterwards) as recurrent parent. In the present paper, the inheritance of the male fertility restoration of NJCMS2A was studied. At the same time, the SSR(simple sequence repeat) marker linked to the restorer gene of NJCMS2A was screened. The main results were as follows:The NJCMS2A×Zhongdou 5 cross was used to study the inheritance of the male fertility restoration of the cytoplasmic-nuclear male-sterile line NJCMS2A. The results showed that the inheritance of the fertility restoration of NJCMS2A was steady among different years. All F₁ plants of the NJCMS2A×Zhongdou 5 cross were male-fertile. The F_1:2 population exhibited male fertility segregation, and the segretation ratio of male-fertile to male-sterile plants fitted a 15:1 ratio underχ² test. The F₁ and F_1:2 results proposed apossible inheritance model of two duplicate dominant genes. The segregation ratio of number of non-segregating male-fertile F_2:3 families:number of 3:1 segregation F_2:3 families:number of 15:1 segregation F_2:3 families fitted a 7:4:4 ratio byχ² test as expected. All the above phenotypic and genotypic segregation data demonstrated the hypothesis that male fertility restoration of NJCMS2A was controlled by two pairs of duplicate dominant genes, which further verified the results of Bai and Gai (2006).One F_1:2 population from the NJCMS2A×Zhongdou 5 cross was chosen randomly to tag the restorer gene of NJCMS2A. The polymorphism between the male-sterile line NJCMS2A and the restorer line Zhongdou 5 was analyzed with 903 pairs of SSR primers selected randomly from the soybean public genetic linkage map reported by Cregan et al. (1999). Among them, 399 pairs showed polymorphism. Based on it, the 399 pairs of SSR primers were used to test the polymorphism between the male-sterile bulk (S bulk) and the male-fertile bulk (F bulk). It was found that 30 pairs from the 399 showed polymorphism between the two bulks. Then the polymorphism among NJCMS2A, Zhongdou 5, S bulk and F bulk were further tested with the 30 pairs of SSR primers. Six pairs of SSR primers from the 30 displayed polymorphism and were used to test the polymorphism among NJCMS2A, Zhongdou 5, S bulk, F bulk, F₁ and F_1:2. The results indicated that four pairs of SSR primers, i.e.Sattl35, Sattl52, Sat₁86 and Satt281, segregated normally according to a ratio of the maternal pattern : heterozygous pattern : paternal pattern as 1:2:1 in the F_1:2 population, while the segregation of Satt030 and Sat₃81 in F_1:2 were extremely biased from the 1:2:1 ratio. Theχ² tests indicated that Sattl35 was linked to the restorer gene of NJCMS2A, whereas Sattl52, Sat₁86 and Satt281 did not. The recombination ratio of the restorer gene of NJCMS2A with Satt135 calculated from the maximum likelihood method was 0.11271, and converted into Kosambi's genetic distance, was 11.47cM. In comparison with the integrated linkage map by Song et al. (2004), the restorer gene of NJCMS2A was located on the linkage group D2.