Improvement Of Ogu CMS Restore Lines In Brassica Napus By Molecular Marker-Assisted Selection

Brassica napus (AⁿAⁿCⁿCⁿ 2n=38) was originated from the hybrids betweeen B. campestris (A^rA^r 2n=20) and B. olercea (C^oC^o 2n=18) through natural crosses follwed by natural doubling of chromosomes. Compared with parental B. rapa, B. napus exhibited narrow germplasm due to short history of domestication. Introgression of gene pool from B. rapa into B. napus can broaden the genetic germplasm of the B. napus. In addition, the genetic differences between A^r from B. campestris and Aⁿ from Brassica napus genomes can provide the genetic basis of intersubgenomic heterosis.The main purpose of this study was to obtain the improved restorer lines of Ogura-INRA cytoplasm male sterility (Ogura-INRA CMS) with the high content of A^r genomes. The new restorer lines were obtained by one time cross-backcross-selfed methods between hui No.7-2407 of restorer line of Ogu cms and No.7-750 (A^rA^rCⁿCⁿ), and employing molecular assisted selection (MAS). Subsequently, the effects of such improvement on the agronomic performance of the restorer lines were evaluated by assay of combining abilities. The main results were as follows:1. Developping a BC₁F₁ population. Hui No.7-2407, a restorer line of Ogu cms, as the non-recurrent parent, and No.7-750, a new formed intregressing B. napus as the recurrent parent, were crossed and then followed by one time backcrossing. In the BC₁F₁ population, 135 of 310 individuals were male fertile, and 76 fertile individuals were selected for the succeeding analysis according to the field performed.2. Clustering 76 male fertile individuals of BC₁F₁ and two perents based on the results of AFLP analysis. In total, about 600 bands in the 78 materials were amplified using 12 AFLP primer combinations, whereas only 64 bands were polymorphic, occupied 13.3%. These polymorphic bands were then applied to cluster by UPGMA method. The results of clustering showed that these materials were classified into two main clusters at the 0.48 level. The accept parent and 44 male fertile individuals of BC₁F₁ were in one cluster, while the recurrent parent and the others were in the other cluster. The Genetic Similarity Index (GSI) among the recurrent parent and 76 individuals of BC₁F₁ ranged from 0.370 to 0.693. What's more, The 76 individuals were divided into three main groups by the GSI. The plants with the GSI varying from 0.300 to 0.500 were in the first group, the plants with the GSI varying from 0.500 to 0.600 were in the second group, and the GSI of plants in the third were varying from 0.600 to 1.000. According to the grouped GSI there were 3 of 19 individuals picked from the first group, 6 of 19 individuals from the second, and 10 of 19 individuals from the third. In total, 19 individuals were selected from the three groups for analyzing their genetic backgrounds.3. Analysis of the genetic background of the 19 individudals in BC₁F₁. A total of 268 clear bands, including 169 polymorphic bands, were obtained in the 19 individudals and two parents of the recurrent parent, Tianman Youcaibai (B. rapa) and Hushuang No.3 (B. napus), using 6 AFLP primer combinations. A_r relatively content of the recurrent parent was calculated according to 169 polymorphic bands. The results showed that the A_r relatively content ranged from 36.5% to 42.5% in all 19 plants. The A_r relatively content in the first group with the GSI varying from 0.300 to 0.500 ranged from 36.5% to 38.4%, ranged from 38.5% to 40.0% in the second group with the GSI varying from 0.500 to 0.600, and ranged from 40.1% to 42.5% in the third group with the GSI varying from 0.600 to 1.000. In conclusion, the individudals with high GSI to recurrent parent were also high in the A^r relatively content. Combinding with evaluation for quality traits, two individuals with middle glucosinolate, low erucic acid and A^r relatively content of 42.5% and 42.1%, respectively, were selected.4. Analysis of the combining abilities. The combining abilities of four characters (plant siliaue numbers,seed number per silique,1000-seed weight and yield per plant) related to yield were done in nine crosses from three cytoplasmic male sterile (CMS) lines, one original restorer line and two improved restorer lines by hand pollination within a North Carolinaâ…¡(NCâ…¡) mating design. The results demonstrated that there were significant difference among restorer lines in the general combining ability (GCA) of siliques per plant, grain weight per plant, and 1000-seeds per silique among the lines; Compared with the original restorer line, hui No.7-2407, the two improved restorer lines were significant higher in the general combining ability (GCA) of siliques per plant, and yeild per plant. The results indicated that the new restorer lines in the general combining ability were significantly improved by this marker-assisted, compared with the original restorer line. 5. Relationships between genetic distances (GD) based on AFLP markers, heterosis and combining ability.5.1 A total of 12 AFLP primer combinations amplified 182 polymorphic bands. The GD between restorer lines and sterilie lines varied from 0.520 to 0.816, with an average of 0.671. The GD between No.A1 and hui 20 was the highest, while the GD between No.A3 and hui No.7-2407 was the lowest. Six varities were divided into two main groups after UPGMA cluster analysis, which was consistent with the origin of the varities.5.2 The method of linear correlation was used to investigate the relationships between genetic distances (GD) based on AFLP markers and hybrid performance and combining ability. The results were that the correlation coefficients between the GD based on AFLP markers and four F₁ traits performance were not significant, and between average GD based on AFLP markers and general combining ability of plant siliaue numbers, 1000-seed weight and yield per plant characters for each parent were not significant, either. In addition, that the correlation coefficients between the GD based on AFLP markers and special combining abilities of plant silique numbers and seed numbers per silique. In conclusion, it was impossible to directly predict heterosis using AFLP genetic distances according to our research.